path: root/activerecord/lib/active_record/base.rb

require 'yaml'
require 'set'
require 'active_support/benchmarkable'
require 'active_support/dependencies'
require 'active_support/descendants_tracker'
require 'active_support/time'
require 'active_support/core_ext/class/attribute'
require 'active_support/core_ext/class/attribute_accessors'
require 'active_support/core_ext/class/delegating_attributes'
require 'active_support/core_ext/class/inheritable_attributes'
require 'active_support/core_ext/array/extract_options'
require 'active_support/core_ext/hash/deep_merge'
require 'active_support/core_ext/hash/indifferent_access'
require 'active_support/core_ext/hash/slice'
require 'active_support/core_ext/string/behavior'
require 'active_support/core_ext/kernel/singleton_class'
require 'active_support/core_ext/module/delegation'
require 'active_support/core_ext/module/deprecation'
require 'active_support/core_ext/module/introspection'
require 'active_support/core_ext/object/duplicable'
require 'active_support/core_ext/object/blank'
require 'arel'
require 'active_record/errors'
require 'active_record/log_subscriber'

module ActiveRecord #:nodoc:
  # = Active Record 
  #
  # Active Record objects don't specify their attributes directly, but rather infer them from the table definition with
  # which they're linked. Adding, removing, and changing attributes and their type is done directly in the database. Any change
  # is instantly reflected in the Active Record objects. The mapping that binds a given Active Record class to a certain
  # database table will happen automatically in most common cases, but can be overwritten for the uncommon ones.
  #
  # See the mapping rules in table_name and the full example in link:files/README.html for more insight.
  #
  # == Creation
  #
  # Active Records accept constructor parameters either in a hash or as a block. The hash method is especially useful when
  # you're receiving the data from somewhere else, like an HTTP request. It works like this:
  #
  #   user = User.new(:name => "David", :occupation => "Code Artist")
  #   user.name # => "David"
  #
  # You can also use block initialization:
  #
  #   user = User.new do |u|
  #     u.name = "David"
  #     u.occupation = "Code Artist"
  #   end
  #
  # And of course you can just create a bare object and specify the attributes after the fact:
  #
  #   user = User.new
  #   user.name = "David"
  #   user.occupation = "Code Artist"
  #
  # == Conditions
  #
  # Conditions can either be specified as a string, array, or hash representing the WHERE-part of an SQL statement.
  # The array form is to be used when the condition input is tainted and requires sanitization. The string form can
  # be used for statements that don't involve tainted data. The hash form works much like the array form, except
  # only equality and range is possible. Examples:
  #
  #   class User < ActiveRecord::Base
  #     def self.authenticate_unsafely(user_name, password)
  #       where("user_name = '#{user_name}' AND password = '#{password}'").first
  #     end
  #
  #     def self.authenticate_safely(user_name, password)
  #       where("user_name = ? AND password = ?", user_name, password).first
  #     end
  #
  #     def self.authenticate_safely_simply(user_name, password)
  #       where(:user_name => user_name, :password => password).first
  #     end
  #   end
  #
  # The <tt>authenticate_unsafely</tt> method inserts the parameters directly into the query and is thus susceptible to SQL-injection
  # attacks if the <tt>user_name</tt> and +password+ parameters come directly from an HTTP request. The <tt>authenticate_safely</tt>  and
  # <tt>authenticate_safely_simply</tt> both will sanitize the <tt>user_name</tt> and +password+ before inserting them in the query,
  # which will ensure that an attacker can't escape the query and fake the login (or worse).
  #
  # When using multiple parameters in the conditions, it can easily become hard to read exactly what the fourth or fifth
  # question mark is supposed to represent. In those cases, you can resort to named bind variables instead. That's done by replacing
  # the question marks with symbols and supplying a hash with values for the matching symbol keys:
  #
  #   Company.where(
  #     "id = :id AND name = :name AND division = :division AND created_at > :accounting_date",
  #     { :id => 3, :name => "37signals", :division => "First", :accounting_date => '2005-01-01' }
  #   ).first
  #
  # Similarly, a simple hash without a statement will generate conditions based on equality with the SQL AND
  # operator. For instance:
  #
  #   Student.where(:first_name => "Harvey", :status => 1)
  #   Student.where(params[:student])
  #
  # A range may be used in the hash to use the SQL BETWEEN operator:
  #
  #   Student.where(:grade => 9..12)
  #
  # An array may be used in the hash to use the SQL IN operator:
  #
  #   Student.where(:grade => [9,11,12])
  #
  # When joining tables, nested hashes or keys written in the form 'table_name.column_name' can be used to qualify the table name of a
  # particular condition. For instance:
  #
  #   Student.joins(:schools).where(:schools => { :type => 'public' })
  #   Student.joins(:schools).where('schools.type' => 'public' )
  #
  # == Overwriting default accessors
  #
  # All column values are automatically available through basic accessors on the Active Record object, but sometimes you
  # want to specialize this behavior. This can be done by overwriting the default accessors (using the same
  # name as the attribute) and calling <tt>read_attribute(attr_name)</tt> and <tt>write_attribute(attr_name, value)</tt> to actually change things.
  # Example:
  #
  #   class Song < ActiveRecord::Base
  #     # Uses an integer of seconds to hold the length of the song
  #
  #     def length=(minutes)
  #       write_attribute(:length, minutes.to_i * 60)
  #     end
  #
  #     def length
  #       read_attribute(:length) / 60
  #     end
  #   end
  #
  # You can alternatively use <tt>self[:attribute]=(value)</tt> and <tt>self[:attribute]</tt> instead of <tt>write_attribute(:attribute, value)</tt> and
  # <tt>read_attribute(:attribute)</tt> as a shorter form.
  #
  # == Attribute query methods
  #
  # In addition to the basic accessors, query methods are also automatically available on the Active Record object.
  # Query methods allow you to test whether an attribute value is present.
  #
  # For example, an Active Record User with the <tt>name</tt> attribute has a <tt>name?</tt> method that you can call
  # to determine whether the user has a name:
  #
  #   user = User.new(:name => "David")
  #   user.name? # => true
  #
  #   anonymous = User.new(:name => "")
  #   anonymous.name? # => false
  #
  # == Accessing attributes before they have been typecasted
  #
  # Sometimes you want to be able to read the raw attribute data without having the column-determined typecast run its course first.
  # That can be done by using the <tt><attribute>_before_type_cast</tt> accessors that all attributes have. For example, if your Account model
  # has a <tt>balance</tt> attribute, you can call <tt>account.balance_before_type_cast</tt> or <tt>account.id_before_type_cast</tt>.
  #
  # This is especially useful in validation situations where the user might supply a string for an integer field and you want to display
  # the original string back in an error message. Accessing the attribute normally would typecast the string to 0, which isn't what you
  # want.
  #
  # == Dynamic attribute-based finders
  #
  # Dynamic attribute-based finders are a cleaner way of getting (and/or creating) objects by simple queries without turning to SQL. They work by
  # appending the name of an attribute to <tt>find_by_</tt>, <tt>find_last_by_</tt>, or <tt>find_all_by_</tt>, so you get finders like <tt>Person.find_by_user_name</tt>,
  # <tt>Person.find_all_by_last_name</tt>, and <tt>Payment.find_by_transaction_id</tt>. So instead of writing
  # <tt>Person.where(:user_name => user_name).first</tt>, you just do <tt>Person.find_by_user_name(user_name)</tt>.
  # And instead of writing <tt>Person.where(:last_name => last_name).all</tt>, you just do <tt>Person.find_all_by_last_name(last_name)</tt>.
  #
  # It's also possible to use multiple attributes in the same find by separating them with "_and_", so you get finders like
  # <tt>Person.find_by_user_name_and_password</tt> or even <tt>Payment.find_by_purchaser_and_state_and_country</tt>. So instead of writing
  # <tt>Person.where(:user_name => user_name, :password => password).first</tt>, you just do
  # <tt>Person.find_by_user_name_and_password(user_name, password)</tt>.
  #
  # It's even possible to call these dynamic finder methods on relations and named scopes. For example :
  #
  #   Payment.order("created_on").find_all_by_amount(50)
  #   Payment.pending.find_last_by_amount(100)
  #
  # The same dynamic finder style can be used to create the object if it doesn't already exist. This dynamic finder is called with
  # <tt>find_or_create_by_</tt> and will return the object if it already exists and otherwise creates it, then returns it. Protected attributes won't be set unless they are given in a block. For example:
  #
  #   # No 'Summer' tag exists
  #   Tag.find_or_create_by_name("Summer") # equal to Tag.create(:name => "Summer")
  #
  #   # Now the 'Summer' tag does exist
  #   Tag.find_or_create_by_name("Summer") # equal to Tag.find_by_name("Summer")
  #
  #   # Now 'Bob' exist and is an 'admin'
  #   User.find_or_create_by_name('Bob', :age => 40) { |u| u.admin = true }
  #
  # Use the <tt>find_or_initialize_by_</tt> finder if you want to return a new record without saving it first. Protected attributes won't be set unless they are given in a block. For example:
  #
  #   # No 'Winter' tag exists
  #   winter = Tag.find_or_initialize_by_name("Winter")
  #   winter.new_record? # true
  #
  # To find by a subset of the attributes to be used for instantiating a new object, pass a hash instead of
  # a list of parameters. For example:
  #
  #   Tag.find_or_create_by_name(:name => "rails", :creator => current_user)
  #
  # That will either find an existing tag named "rails", or create a new one while setting the user that created it.
  #
  # == Saving arrays, hashes, and other non-mappable objects in text columns
  #
  # Active Record can serialize any object in text columns using YAML. To do so, you must specify this with a call to the class method +serialize+.
  # This makes it possible to store arrays, hashes, and other non-mappable objects without doing any additional work. Example:
  #
  #   class User < ActiveRecord::Base
  #     serialize :preferences
  #   end
  #
  #   user = User.create(:preferences => { "background" => "black", "display" => large })
  #   User.find(user.id).preferences # => { "background" => "black", "display" => large }
  #
  # You can also specify a class option as the second parameter that'll raise an exception if a serialized object is retrieved as a
  # descendant of a class not in the hierarchy. Example:
  #
  #   class User < ActiveRecord::Base
  #     serialize :preferences, Hash
  #   end
  #
  #   user = User.create(:preferences => %w( one two three ))
  #   User.find(user.id).preferences    # raises SerializationTypeMismatch
  #
  # == Single table inheritance
  #
  # Active Record allows inheritance by storing the name of the class in a column that by default is named "type" (can be changed
  # by overwriting <tt>Base.inheritance_column</tt>). This means that an inheritance looking like this:
  #
  #   class Company < ActiveRecord::Base; end
  #   class Firm < Company; end
  #   class Client < Company; end
  #   class PriorityClient < Client; end
  #
  # When you do <tt>Firm.create(:name => "37signals")</tt>, this record will be saved in the companies table with type = "Firm". You can then
  # fetch this row again using <tt>Company.where(:name => '37signals').first</tt> and it will return a Firm object.
  #
  # If you don't have a type column defined in your table, single-table inheritance won't be triggered. In that case, it'll work just
  # like normal subclasses with no special magic for differentiating between them or reloading the right type with find.
  #
  # Note, all the attributes for all the cases are kept in the same table. Read more:
  # http://www.martinfowler.com/eaaCatalog/singleTableInheritance.html
  #
  # == Connection to multiple databases in different models
  #
  # Connections are usually created through ActiveRecord::Base.establish_connection and retrieved by ActiveRecord::Base.connection.
  # All classes inheriting from ActiveRecord::Base will use this connection. But you can also set a class-specific connection.
  # For example, if Course is an ActiveRecord::Base, but resides in a different database, you can just say <tt>Course.establish_connection</tt>
  # and Course and all of its subclasses will use this connection instead.
  #
  # This feature is implemented by keeping a connection pool in ActiveRecord::Base that is a Hash indexed by the class. If a connection is
  # requested, the retrieve_connection method will go up the class-hierarchy until a connection is found in the connection pool.
  #
  # == Exceptions
  #
  # * ActiveRecordError - Generic error class and superclass of all other errors raised by Active Record.
  # * AdapterNotSpecified - The configuration hash used in <tt>establish_connection</tt> didn't include an
  #   <tt>:adapter</tt> key.
  # * AdapterNotFound - The <tt>:adapter</tt> key used in <tt>establish_connection</tt> specified a non-existent adapter
  #   (or a bad spelling of an existing one).
  # * AssociationTypeMismatch - The object assigned to the association wasn't of the type specified in the association definition.
  # * SerializationTypeMismatch - The serialized object wasn't of the class specified as the second parameter.
  # * ConnectionNotEstablished+ - No connection has been established. Use <tt>establish_connection</tt> before querying.
  # * RecordNotFound - No record responded to the +find+ method. Either the row with the given ID doesn't exist
  #   or the row didn't meet the additional restrictions. Some +find+ calls do not raise this exception to signal
  #   nothing was found, please check its documentation for further details.
  # * StatementInvalid - The database server rejected the SQL statement. The precise error is added in the message.
  # * MultiparameterAssignmentErrors - Collection of errors that occurred during a mass assignment using the
  #   <tt>attributes=</tt> method. The +errors+ property of this exception contains an array of AttributeAssignmentError
  #   objects that should be inspected to determine which attributes triggered the errors.
  # * AttributeAssignmentError - An error occurred while doing a mass assignment through the <tt>attributes=</tt> method.
  #   You can inspect the +attribute+ property of the exception object to determine which attribute triggered the error.
  #
  # *Note*: The attributes listed are class-level attributes (accessible from both the class and instance level).
  # So it's possible to assign a logger to the class through <tt>Base.logger=</tt> which will then be used by all
  # instances in the current object space.
  class Base
    ##
    # :singleton-method:
    # Accepts a logger conforming to the interface of Log4r or the default Ruby 1.8+ Logger class, which is then passed
    # on to any new database connections made and which can be retrieved on both a class and instance level by calling +logger+.
    cattr_accessor :logger, :instance_writer => false

    class << self
      def reset_subclasses #:nodoc:
        ActiveSupport::Deprecation.warn 'ActiveRecord::Base.reset_subclasses no longer does anything in Rails 3. It will be removed in the final release; please update your apps and plugins.', caller
      end

      def subclasses
        descendants
      end

      deprecate :subclasses => :descendants
    end

    ##
    # :singleton-method:
    # Contains the database configuration - as is typically stored in config/database.yml -
    # as a Hash.
    #
    # For example, the following database.yml...
    #
    #   development:
    #     adapter: sqlite3
    #     database: db/development.sqlite3
    #
    #   production:
    #     adapter: sqlite3
    #     database: db/production.sqlite3
    #
    # ...would result in ActiveRecord::Base.configurations to look like this:
    #
    #   {
    #      'development' => {
    #         'adapter'  => 'sqlite3',
    #         'database' => 'db/development.sqlite3'
    #      },
    #      'production' => {
    #         'adapter'  => 'sqlite3',
    #         'database' => 'db/production.sqlite3'
    #      }
    #   }
    cattr_accessor :configurations, :instance_writer => false
    @@configurations = {}

    ##
    # :singleton-method:
    # Accessor for the prefix type that will be prepended to every primary key column name. The options are :table_name and
    # :table_name_with_underscore. If the first is specified, the Product class will look for "productid" instead of "id" as
    # the primary column. If the latter is specified, the Product class will look for "product_id" instead of "id". Remember
    # that this is a global setting for all Active Records.
    cattr_accessor :primary_key_prefix_type, :instance_writer => false
    @@primary_key_prefix_type = nil

    ##
    # :singleton-method:
    # Accessor for the name of the prefix string to prepend to every table name. So if set to "basecamp_", all
    # table names will be named like "basecamp_projects", "basecamp_people", etc. This is a convenient way of creating a namespace
    # for tables in a shared database. By default, the prefix is the empty string.
    #
    # If you are organising your models within modules you can add a prefix to the models within a namespace by defining
    # a singleton method in the parent module called table_name_prefix which returns your chosen prefix.
    class_attribute :table_name_prefix, :instance_writer => false
    self.table_name_prefix = ""

    ##
    # :singleton-method:
    # Works like +table_name_prefix+, but appends instead of prepends (set to "_basecamp" gives "projects_basecamp",
    # "people_basecamp"). By default, the suffix is the empty string.
    class_attribute :table_name_suffix, :instance_writer => false
    self.table_name_suffix = ""

    ##
    # :singleton-method:
    # Indicates whether table names should be the pluralized versions of the corresponding class names.
    # If true, the default table name for a Product class will be +products+. If false, it would just be +product+.
    # See table_name for the full rules on table/class naming. This is true, by default.
    cattr_accessor :pluralize_table_names, :instance_writer => false
    @@pluralize_table_names = true

    ##
    # :singleton-method:
    # Determines whether to use Time.local (using :local) or Time.utc (using :utc) when pulling dates and times from the database.
    # This is set to :local by default.
    cattr_accessor :default_timezone, :instance_writer => false
    @@default_timezone = :local

    ##
    # :singleton-method:
    # Specifies the format to use when dumping the database schema with Rails'
    # Rakefile.  If :sql, the schema is dumped as (potentially database-
    # specific) SQL statements.  If :ruby, the schema is dumped as an
    # ActiveRecord::Schema file which can be loaded into any database that
    # supports migrations.  Use :ruby if you want to have different database
    # adapters for, e.g., your development and test environments.
    cattr_accessor :schema_format , :instance_writer => false
    @@schema_format = :ruby

    ##
    # :singleton-method:
    # Specify whether or not to use timestamps for migration versions
    cattr_accessor :timestamped_migrations , :instance_writer => false
    @@timestamped_migrations = true

    # Determine whether to store the full constant name including namespace when using STI
    superclass_delegating_accessor :store_full_sti_class
    self.store_full_sti_class = true

    # Stores the default scope for the class
    class_inheritable_accessor :default_scoping, :instance_writer => false
    self.default_scoping = []

    class << self # Class methods
      def colorize_logging(*args)
        ActiveSupport::Deprecation.warn "ActiveRecord::Base.colorize_logging and " <<
          "config.active_record.colorize_logging are deprecated. Please use " <<
          "Rails::LogSubscriber.colorize_logging or config.colorize_logging instead", caller
      end
      alias :colorize_logging= :colorize_logging

      delegate :find, :first, :last, :all, :destroy, :destroy_all, :exists?, :delete, :delete_all, :update, :update_all, :to => :scoped
      delegate :find_each, :find_in_batches, :to => :scoped
      delegate :select, :group, :order, :limit, :joins, :where, :preload, :eager_load, :includes, :from, :lock, :readonly, :having, :create_with, :to => :scoped
      delegate :count, :average, :minimum, :maximum, :sum, :calculate, :to => :scoped

      # Executes a custom SQL query against your database and returns all the results.  The results will
      # be returned as an array with columns requested encapsulated as attributes of the model you call
      # this method from.  If you call <tt>Product.find_by_sql</tt> then the results will be returned in
      # a Product object with the attributes you specified in the SQL query.
      #
      # If you call a complicated SQL query which spans multiple tables the columns specified by the
      # SELECT will be attributes of the model, whether or not they are columns of the corresponding
      # table.
      #
      # The +sql+ parameter is a full SQL query as a string.  It will be called as is, there will be
      # no database agnostic conversions performed.  This should be a last resort because using, for example,
      # MySQL specific terms will lock you to using that particular database engine or require you to
      # change your call if you switch engines.
      #
      # ==== Examples
      #   # A simple SQL query spanning multiple tables
      #   Post.find_by_sql "SELECT p.title, c.author FROM posts p, comments c WHERE p.id = c.post_id"
      #   > [#<Post:0x36bff9c @attributes={"title"=>"Ruby Meetup", "first_name"=>"Quentin"}>, ...]
      #
      #   # You can use the same string replacement techniques as you can with ActiveRecord#find
      #   Post.find_by_sql ["SELECT title FROM posts WHERE author = ? AND created > ?", author_id, start_date]
      #   > [#<Post:0x36bff9c @attributes={"first_name"=>"The Cheap Man Buys Twice"}>, ...]
      def find_by_sql(sql)
        connection.select_all(sanitize_sql(sql), "#{name} Load").collect! { |record| instantiate(record) }
      end

      # Creates an object (or multiple objects) and saves it to the database, if validations pass.
      # The resulting object is returned whether the object was saved successfully to the database or not.
      #
      # The +attributes+ parameter can be either be a Hash or an Array of Hashes.  These Hashes describe the
      # attributes on the objects that are to be created.
      #
      # ==== Examples
      #   # Create a single new object
      #   User.create(:first_name => 'Jamie')
      #
      #   # Create an Array of new objects
      #   User.create([{ :first_name => 'Jamie' }, { :first_name => 'Jeremy' }])
      #
      #   # Create a single object and pass it into a block to set other attributes.
      #   User.create(:first_name => 'Jamie') do |u|
      #     u.is_admin = false
      #   end
      #
      #   # Creating an Array of new objects using a block, where the block is executed for each object:
      #   User.create([{ :first_name => 'Jamie' }, { :first_name => 'Jeremy' }]) do |u|
      #     u.is_admin = false
      #   end
      def create(attributes = nil, &block)
        if attributes.is_a?(Array)
          attributes.collect { |attr| create(attr, &block) }
        else
          object = new(attributes)
          yield(object) if block_given?
          object.save
          object
        end
      end

      # Returns the result of an SQL statement that should only include a COUNT(*) in the SELECT part.
      # The use of this method should be restricted to complicated SQL queries that can't be executed
      # using the ActiveRecord::Calculations class methods.  Look into those before using this.
      #
      # ==== Parameters
      #
      # * +sql+ - An SQL statement which should return a count query from the database, see the example below.
      #
      # ==== Examples
      #
      #   Product.count_by_sql "SELECT COUNT(*) FROM sales s, customers c WHERE s.customer_id = c.id"
      def count_by_sql(sql)
        sql = sanitize_conditions(sql)
        connection.select_value(sql, "#{name} Count").to_i
      end

      # Attributes named in this macro are protected from mass-assignment,
      # such as <tt>new(attributes)</tt>,
      # <tt>update_attributes(attributes)</tt>, or
      # <tt>attributes=(attributes)</tt>.
      #
      # Mass-assignment to these attributes will simply be ignored, to assign
      # to them you can use direct writer methods. This is meant to protect
      # sensitive attributes from being overwritten by malicious users
      # tampering with URLs or forms.
      #
      #   class Customer < ActiveRecord::Base
      #     attr_protected :credit_rating
      #   end
      #
      #   customer = Customer.new("name" => David, "credit_rating" => "Excellent")
      #   customer.credit_rating # => nil
      #   customer.attributes = { "description" => "Jolly fellow", "credit_rating" => "Superb" }
      #   customer.credit_rating # => nil
      #
      #   customer.credit_rating = "Average"
      #   customer.credit_rating # => "Average"
      #
      # To start from an all-closed default and enable attributes as needed,
      # have a look at +attr_accessible+.
      #
      # If the access logic of your application is richer you can use <tt>Hash#except</tt>
      # or <tt>Hash#slice</tt> to sanitize the hash of parameters before they are
      # passed to Active Record.
      #
      # For example, it could be the case that the list of protected attributes
      # for a given model depends on the role of the user:
      #
      #   # Assumes plan_id is not protected because it depends on the role.
      #   params[:account] = params[:account].except(:plan_id) unless admin?
      #   @account.update_attributes(params[:account])
      #
      # Note that +attr_protected+ is still applied to the received hash. Thus,
      # with this technique you can at most _extend_ the list of protected
      # attributes for a particular mass-assignment call.
      def attr_protected(*attributes)
        write_inheritable_attribute(:attr_protected, Set.new(attributes.map {|a| a.to_s}) + (protected_attributes || []))
      end

      # Returns an array of all the attributes that have been protected from mass-assignment.
      def protected_attributes # :nodoc:
        read_inheritable_attribute(:attr_protected)
      end

      # Specifies a white list of model attributes that can be set via
      # mass-assignment, such as <tt>new(attributes)</tt>,
      # <tt>update_attributes(attributes)</tt>, or
      # <tt>attributes=(attributes)</tt>
      #
      # This is the opposite of the +attr_protected+ macro: Mass-assignment
      # will only set attributes in this list, to assign to the rest of
      # attributes you can use direct writer methods. This is meant to protect
      # sensitive attributes from being overwritten by malicious users
      # tampering with URLs or forms. If you'd rather start from an all-open
      # default and restrict attributes as needed, have a look at
      # +attr_protected+.
      #
      #   class Customer < ActiveRecord::Base
      #     attr_accessible :name, :nickname
      #   end
      #
      #   customer = Customer.new(:name => "David", :nickname => "Dave", :credit_rating => "Excellent")
      #   customer.credit_rating # => nil
      #   customer.attributes = { :name => "Jolly fellow", :credit_rating => "Superb" }
      #   customer.credit_rating # => nil
      #
      #   customer.credit_rating = "Average"
      #   customer.credit_rating # => "Average"
      #
      # If the access logic of your application is richer you can use <tt>Hash#except</tt>
      # or <tt>Hash#slice</tt> to sanitize the hash of parameters before they are
      # passed to Active Record.
      #
      # For example, it could be the case that the list of accessible attributes
      # for a given model depends on the role of the user:
      #
      #   # Assumes plan_id is accessible because it depends on the role.
      #   params[:account] = params[:account].except(:plan_id) unless admin?
      #   @account.update_attributes(params[:account])
      #
      # Note that +attr_accessible+ is still applied to the received hash. Thus,
      # with this technique you can at most _narrow_ the list of accessible
      # attributes for a particular mass-assignment call.
      def attr_accessible(*attributes)
        write_inheritable_attribute(:attr_accessible, Set.new(attributes.map(&:to_s)) + (accessible_attributes || []))
      end

      # Returns an array of all the attributes that have been made accessible to mass-assignment.
      def accessible_attributes # :nodoc:
        read_inheritable_attribute(:attr_accessible)
      end

       # Attributes listed as readonly can be set for a new record, but will be ignored in database updates afterwards.
       def attr_readonly(*attributes)
         write_inheritable_attribute(:attr_readonly, Set.new(attributes.map(&:to_s)) + (readonly_attributes || []))
       end

       # Returns an array of all the attributes that have been specified as readonly.
       def readonly_attributes
         read_inheritable_attribute(:attr_readonly) || []
       end

      # If you have an attribute that needs to be saved to the database as an object, and retrieved as the same object,
      # then specify the name of that attribute using this method and it will be handled automatically.
      # The serialization is done through YAML. If +class_name+ is specified, the serialized object must be of that
      # class on retrieval or SerializationTypeMismatch will be raised.
      #
      # ==== Parameters
      #
      # * +attr_name+ - The field name that should be serialized.
      # * +class_name+ - Optional, class name that the object type should be equal to.
      #
      # ==== Example
      #   # Serialize a preferences attribute
      #   class User
      #     serialize :preferences
      #   end
      def serialize(attr_name, class_name = Object)
        serialized_attributes[attr_name.to_s] = class_name
      end

      # Returns a hash of all the attributes that have been specified for serialization as keys and their class restriction as values.
      def serialized_attributes
        read_inheritable_attribute(:attr_serialized) or write_inheritable_attribute(:attr_serialized, {})
      end

      # Guesses the table name (in forced lower-case) based on the name of the class in the inheritance hierarchy descending
      # directly from ActiveRecord::Base. So if the hierarchy looks like: Reply < Message < ActiveRecord::Base, then Message is used
      # to guess the table name even when called on Reply. The rules used to do the guess are handled by the Inflector class
      # in Active Support, which knows almost all common English inflections. You can add new inflections in config/initializers/inflections.rb.
      #
      # Nested classes are given table names prefixed by the singular form of
      # the parent's table name. Enclosing modules are not considered.
      #
      # ==== Examples
      #
      #   class Invoice < ActiveRecord::Base; end;
      #   file                  class               table_name
      #   invoice.rb            Invoice             invoices
      #
      #   class Invoice < ActiveRecord::Base; class Lineitem < ActiveRecord::Base; end; end;
      #   file                  class               table_name
      #   invoice.rb            Invoice::Lineitem   invoice_lineitems
      #
      #   module Invoice; class Lineitem < ActiveRecord::Base; end; end;
      #   file                  class               table_name
      #   invoice/lineitem.rb   Invoice::Lineitem   lineitems
      #
      # Additionally, the class-level +table_name_prefix+ is prepended and the
      # +table_name_suffix+ is appended.  So if you have "myapp_" as a prefix,
      # the table name guess for an Invoice class becomes "myapp_invoices".
      # Invoice::Lineitem becomes "myapp_invoice_lineitems".
      #
      # You can also overwrite this class method to allow for unguessable
      # links, such as a Mouse class with a link to a "mice" table. Example:
      #
      #   class Mouse < ActiveRecord::Base
      #     set_table_name "mice"
      #   end
      def table_name
        reset_table_name
      end

      # Returns a quoted version of the table name, used to construct SQL statements.
      def quoted_table_name
        @quoted_table_name ||= connection.quote_table_name(table_name)
      end

      # Computes the table name, (re)sets it internally, and returns it.
      def reset_table_name #:nodoc:
        self.table_name = compute_table_name
      end

      def full_table_name_prefix #:nodoc:
        (parents.detect{ |p| p.respond_to?(:table_name_prefix) } || self).table_name_prefix
      end

      # Defines the column name for use with single table inheritance
      # -- can be set in subclasses like so: self.inheritance_column = "type_id"
      def inheritance_column
        @inheritance_column ||= "type".freeze
      end

      # Lazy-set the sequence name to the connection's default.  This method
      # is only ever called once since set_sequence_name overrides it.
      def sequence_name #:nodoc:
        reset_sequence_name
      end

      def reset_sequence_name #:nodoc:
        default = connection.default_sequence_name(table_name, primary_key)
        set_sequence_name(default)
        default
      end

      # Sets the table name to use to the given value, or (if the value
      # is nil or false) to the value returned by the given block.
      #
      #   class Project < ActiveRecord::Base
      #     set_table_name "project"
      #   end
      def set_table_name(value = nil, &block)
        @quoted_table_name = nil
        define_attr_method :table_name, value, &block
      end
      alias :table_name= :set_table_name

      # Sets the name of the inheritance column to use to the given value,
      # or (if the value # is nil or false) to the value returned by the
      # given block.
      #
      #   class Project < ActiveRecord::Base
      #     set_inheritance_column do
      #       original_inheritance_column + "_id"
      #     end
      #   end
      def set_inheritance_column(value = nil, &block)
        define_attr_method :inheritance_column, value, &block
      end
      alias :inheritance_column= :set_inheritance_column

      # Sets the name of the sequence to use when generating ids to the given
      # value, or (if the value is nil or false) to the value returned by the
      # given block. This is required for Oracle and is useful for any
      # database which relies on sequences for primary key generation.
      #
      # If a sequence name is not explicitly set when using Oracle or Firebird,
      # it will default to the commonly used pattern of: #{table_name}_seq
      #
      # If a sequence name is not explicitly set when using PostgreSQL, it
      # will discover the sequence corresponding to your primary key for you.
      #
      #   class Project < ActiveRecord::Base
      #     set_sequence_name "projectseq"   # default would have been "project_seq"
      #   end
      def set_sequence_name(value = nil, &block)
        define_attr_method :sequence_name, value, &block
      end
      alias :sequence_name= :set_sequence_name

      # Indicates whether the table associated with this class exists
      def table_exists?
        connection.table_exists?(table_name)
      end

      # Returns an array of column objects for the table associated with this class.
      def columns
        unless defined?(@columns) && @columns
          @columns = connection.columns(table_name, "#{name} Columns")
          @columns.each { |column| column.primary = column.name == primary_key }
        end
        @columns
      end

      # Returns a hash of column objects for the table associated with this class.
      def columns_hash
        @columns_hash ||= columns.inject({}) { |hash, column| hash[column.name] = column; hash }
      end

      # Returns an array of column names as strings.
      def column_names
        @column_names ||= columns.map { |column| column.name }
      end

      # Returns an array of column objects where the primary id, all columns ending in "_id" or "_count",
      # and columns used for single table inheritance have been removed.
      def content_columns
        @content_columns ||= columns.reject { |c| c.primary || c.name =~ /(_id|_count)$/ || c.name == inheritance_column }
      end

      # Returns a hash of all the methods added to query each of the columns in the table with the name of the method as the key
      # and true as the value. This makes it possible to do O(1) lookups in respond_to? to check if a given method for attribute
      # is available.
      def column_methods_hash #:nodoc:
        @dynamic_methods_hash ||= column_names.inject(Hash.new(false)) do |methods, attr|
          attr_name = attr.to_s
          methods[attr.to_sym]       = attr_name
          methods["#{attr}=".to_sym] = attr_name
          methods["#{attr}?".to_sym] = attr_name
          methods["#{attr}_before_type_cast".to_sym] = attr_name
          methods
        end
      end

      # Resets all the cached information about columns, which will cause them
      # to be reloaded on the next request.
      #
      # The most common usage pattern for this method is probably in a migration,
      # when just after creating a table you want to populate it with some default
      # values, eg:
      #
      #  class CreateJobLevels < ActiveRecord::Migration
      #    def self.up
      #      create_table :job_levels do |t|
      #        t.integer :id
      #        t.string :name
      #
      #        t.timestamps
      #      end
      #
      #      JobLevel.reset_column_information
      #      %w{assistant executive manager director}.each do |type|
      #        JobLevel.create(:name => type)
      #      end
      #    end
      #
      #    def self.down
      #      drop_table :job_levels
      #    end
      #  end
      def reset_column_information
        undefine_attribute_methods
        @column_names = @columns = @columns_hash = @content_columns = @dynamic_methods_hash = @inheritance_column = nil
        @arel_engine = @relation = @arel_table = nil
      end

      def reset_column_information_and_inheritable_attributes_for_all_subclasses#:nodoc:
        descendants.each { |klass| klass.reset_inheritable_attributes; klass.reset_column_information }
      end

      def attribute_method?(attribute)
        super || (table_exists? && column_names.include?(attribute.to_s.sub(/=$/, '')))
      end

      # Set the lookup ancestors for ActiveModel.
      def lookup_ancestors #:nodoc:
        klass = self
        classes = [klass]
        while klass != klass.base_class
          classes << klass = klass.superclass
        end
        classes
      rescue
        # OPTIMIZE this rescue is to fix this test: ./test/cases/reflection_test.rb:56:in `test_human_name_for_column'
        # Apparently the method base_class causes some trouble.
        # It now works for sure.
        [self]
      end

      # Set the i18n scope to overwrite ActiveModel.
      def i18n_scope #:nodoc:
        :activerecord
      end

      # True if this isn't a concrete subclass needing a STI type condition.
      def descends_from_active_record?
        if superclass.abstract_class?
          superclass.descends_from_active_record?
        else
          superclass == Base || !columns_hash.include?(inheritance_column)
        end
      end

      def finder_needs_type_condition? #:nodoc:
        # This is like this because benchmarking justifies the strange :false stuff
        :true == (@finder_needs_type_condition ||= descends_from_active_record? ? :false : :true)
      end

      # Returns a string like 'Post id:integer, title:string, body:text'
      def inspect
        if self == Base
          super
        elsif abstract_class?
          "#{super}(abstract)"
        elsif table_exists?
          attr_list = columns.map { |c| "#{c.name}: #{c.type}" } * ', '
          "#{super}(#{attr_list})"
        else
          "#{super}(Table doesn't exist)"
        end
      end

      def quote_value(value, column = nil) #:nodoc:
        connection.quote(value,column)
      end

      # Used to sanitize objects before they're used in an SQL SELECT statement. Delegates to <tt>connection.quote</tt>.
      def sanitize(object) #:nodoc:
        connection.quote(object)
      end

      # Overwrite the default class equality method to provide support for association proxies.
      def ===(object)
        object.is_a?(self)
      end

      # Returns the base AR subclass that this class descends from. If A
      # extends AR::Base, A.base_class will return A. If B descends from A
      # through some arbitrarily deep hierarchy, B.base_class will return A.
      #
      # If B < A and C < B and if A is an abstract_class then both B.base_class
      # and C.base_class would return B as the answer since A is an abstract_class.
      def base_class
        class_of_active_record_descendant(self)
      end

      # Set this to true if this is an abstract class (see <tt>abstract_class?</tt>).
      attr_accessor :abstract_class

      # Returns whether this class is an abstract class or not.
      def abstract_class?
        defined?(@abstract_class) && @abstract_class == true
      end

      def respond_to?(method_id, include_private = false)
        if match = DynamicFinderMatch.match(method_id)
          return true if all_attributes_exists?(match.attribute_names)
        elsif match = DynamicScopeMatch.match(method_id)
          return true if all_attributes_exists?(match.attribute_names)
        end

        super
      end

      def sti_name
        store_full_sti_class ? name : name.demodulize
      end

      def relation
        @relation ||= Relation.new(self, arel_table)
        finder_needs_type_condition? ? @relation.where(type_condition) : @relation
      end

      def arel_table
        @arel_table ||= Arel::Table.new(table_name, :engine => arel_engine)
      end

      def arel_engine
        @arel_engine ||= begin
          if self == ActiveRecord::Base
            Arel::Table.engine
          else
            connection_handler.connection_pools[name] ? Arel::Sql::Engine.new(self) : superclass.arel_engine
          end
        end
      end

      # Returns a scope for this class without taking into account the default_scope.
      #
      #   class Post < ActiveRecord::Base
      #     default_scope :published => true
      #   end
      #
      #   Post.all          # Fires "SELECT * FROM posts WHERE published = true"
      #   Post.unscoped.all # Fires "SELECT * FROM posts"
      #
      # This method also accepts a block meaning that all queries inside the block will
      # not use the default_scope:
      #
      #   Post.unscoped {
      #     limit(10) # Fires "SELECT * FROM posts LIMIT 10"
      #   }
      #
      def unscoped
        block_given? ? relation.scoping { yield } : relation
      end

      def scoped_methods #:nodoc:
        key = :"#{self}_scoped_methods"
        Thread.current[key] = Thread.current[key].presence || self.default_scoping.dup
      end

      private
        # Finder methods must instantiate through this method to work with the
        # single-table inheritance model that makes it possible to create
        # objects of different types from the same table.
        def instantiate(record)
          object = find_sti_class(record[inheritance_column]).allocate

          object.instance_variable_set(:@attributes, record)
          object.instance_variable_set(:@attributes_cache, {})
          object.instance_variable_set(:@new_record, false)
          object.instance_variable_set(:@readonly, false)
          object.instance_variable_set(:@destroyed, false)
          object.instance_variable_set(:@marked_for_destruction, false)
          object.instance_variable_set(:@previously_changed, {})
          object.instance_variable_set(:@changed_attributes, {})

          object.send(:_run_find_callbacks)
          object.send(:_run_initialize_callbacks)

          object
        end

        def find_sti_class(type_name)
          if type_name.blank? || !columns_hash.include?(inheritance_column)
            self
          else
            begin
              compute_type(type_name)
            rescue NameError
              raise SubclassNotFound,
                "The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. " +
                "This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. " +
                "Please rename this column if you didn't intend it to be used for storing the inheritance class " +
                "or overwrite #{name}.inheritance_column to use another column for that information."
            end
          end
        end

        def construct_finder_arel(options = {}, scope = nil)
          relation = options.is_a?(Hash) ? unscoped.apply_finder_options(options) : unscoped.merge(options)
          relation = scope.merge(relation) if scope
          relation
        end

        def type_condition
          sti_column = arel_table[inheritance_column]
          condition = sti_column.eq(sti_name)
          descendants.each { |subclass| condition = condition.or(sti_column.eq(subclass.sti_name)) }

          condition
        end

        # Guesses the table name, but does not decorate it with prefix and suffix information.
        def undecorated_table_name(class_name = base_class.name)
          table_name = class_name.to_s.demodulize.underscore
          table_name = table_name.pluralize if pluralize_table_names
          table_name
        end

        # Computes and returns a table name according to default conventions.
        def compute_table_name
          base = base_class
          if self == base
            # Nested classes are prefixed with singular parent table name.
            if parent < ActiveRecord::Base && !parent.abstract_class?
              contained = parent.table_name
              contained = contained.singularize if parent.pluralize_table_names
              contained << '_'
            end
            "#{full_table_name_prefix}#{contained}#{undecorated_table_name(name)}#{table_name_suffix}"
          else
            # STI subclasses always use their superclass' table.
            base.table_name
          end
        end

        # Enables dynamic finders like <tt>find_by_user_name(user_name)</tt> and <tt>find_by_user_name_and_password(user_name, password)</tt>
        # that are turned into <tt>where(:user_name => user_name).first</tt> and <tt>where(:user_name => user_name, :password => :password).first</tt>
        # respectively. Also works for <tt>all</tt> by using <tt>find_all_by_amount(50)</tt> that is turned into <tt>where(:amount => 50).all</tt>.
        #
        # It's even possible to use all the additional parameters to +find+. For example, the full interface for +find_all_by_amount+
        # is actually <tt>find_all_by_amount(amount, options)</tt>.
        #
        # Each dynamic finder, scope or initializer/creator is also defined in the class after it is first invoked, so that future
        # attempts to use it do not run through method_missing.
        def method_missing(method_id, *arguments, &block)
          if match = DynamicFinderMatch.match(method_id)
            attribute_names = match.attribute_names
            super unless all_attributes_exists?(attribute_names)
            if match.finder?
              options = arguments.extract_options!
              relation = options.any? ? construct_finder_arel(options, current_scoped_methods) : scoped
              relation.send :find_by_attributes, match, attribute_names, *arguments
            elsif match.instantiator?
              scoped.send :find_or_instantiator_by_attributes, match, attribute_names, *arguments, &block
            end
          elsif match = DynamicScopeMatch.match(method_id)
            attribute_names = match.attribute_names
            super unless all_attributes_exists?(attribute_names)
            if match.scope?
              self.class_eval <<-METHOD, __FILE__, __LINE__ + 1
                def self.#{method_id}(*args)                        # def self.scoped_by_user_name_and_password(*args)
                  options = args.extract_options!                   #   options = args.extract_options!
                  attributes = construct_attributes_from_arguments( #   attributes = construct_attributes_from_arguments(
                    [:#{attribute_names.join(',:')}], args          #     [:user_name, :password], args
                  )                                                 #   )
                                                                    #
                  scoped(:conditions => attributes)                 #   scoped(:conditions => attributes)
                end                                                 # end
              METHOD
              send(method_id, *arguments)
            end
          else
            super
          end
        end

        def construct_attributes_from_arguments(attribute_names, arguments)
          attributes = {}
          attribute_names.each_with_index { |name, idx| attributes[name] = arguments[idx] }
          attributes
        end

        # Similar in purpose to +expand_hash_conditions_for_aggregates+.
        def expand_attribute_names_for_aggregates(attribute_names)
          expanded_attribute_names = []
          attribute_names.each do |attribute_name|
            unless (aggregation = reflect_on_aggregation(attribute_name.to_sym)).nil?
              aggregate_mapping(aggregation).each do |field_attr, aggregate_attr|
                expanded_attribute_names << field_attr
              end
            else
              expanded_attribute_names << attribute_name
            end
          end
          expanded_attribute_names
        end

        def all_attributes_exists?(attribute_names)
          attribute_names = expand_attribute_names_for_aggregates(attribute_names)
          attribute_names.all? { |name| column_methods_hash.include?(name.to_sym) }
        end

      protected
        # Scope parameters to method calls within the block.  Takes a hash of method_name => parameters hash.
        # method_name may be <tt>:find</tt> or <tt>:create</tt>. <tt>:find</tt> parameter is <tt>Relation</tt> while
        # <tt>:create</tt> parameters are an attributes hash.
        #
        #   class Article < ActiveRecord::Base
        #     def self.create_with_scope
        #       with_scope(:find => where(:blog_id => 1), :create => { :blog_id => 1 }) do
        #         find(1) # => SELECT * from articles WHERE blog_id = 1 AND id = 1
        #         a = create(1)
        #         a.blog_id # => 1
        #       end
        #     end
        #   end
        #
        # In nested scopings, all previous parameters are overwritten by the innermost rule, with the exception of
        # <tt>where</tt>, <tt>includes</tt>, and <tt>joins</tt> operations in <tt>Relation</tt>, which are merged.
        #
        # <tt>joins</tt> operations are uniqued so multiple scopes can join in the same table without table aliasing
        # problems.  If you need to join multiple tables, but still want one of the tables to be uniqued, use the
        # array of strings format for your joins.
        #
        #   class Article < ActiveRecord::Base
        #     def self.find_with_scope
        #       with_scope(:find => where(:blog_id => 1).limit(1), :create => { :blog_id => 1 }) do
        #         with_scope(:find => limit(10)) do
        #           all # => SELECT * from articles WHERE blog_id = 1 LIMIT 10
        #         end
        #         with_scope(:find => where(:author_id => 3)) do
        #           all # => SELECT * from articles WHERE blog_id = 1 AND author_id = 3 LIMIT 1
        #         end
        #       end
        #     end
        #   end
        #
        # You can ignore any previous scopings by using the <tt>with_exclusive_scope</tt> method.
        #
        #   class Article < ActiveRecord::Base
        #     def self.find_with_exclusive_scope
        #       with_scope(:find => where(:blog_id => 1).limit(1)) do
        #         with_exclusive_scope(:find => limit(10))
        #           all # => SELECT * from articles LIMIT 10
        #         end
        #       end
        #     end
        #   end
        #
        # *Note*: the +:find+ scope also has effect on update and deletion methods,
        # like +update_all+ and +delete_all+.
        def with_scope(method_scoping = {}, action = :merge, &block)
          method_scoping = method_scoping.method_scoping if method_scoping.respond_to?(:method_scoping)

          if method_scoping.is_a?(Hash)
            # Dup first and second level of hash (method and params).
            method_scoping = method_scoping.inject({}) do |hash, (method, params)|
              hash[method] = (params == true) ? params : params.dup
              hash
            end

            method_scoping.assert_valid_keys([ :find, :create ])
            relation = construct_finder_arel(method_scoping[:find] || {})

            if current_scoped_methods && current_scoped_methods.create_with_value && method_scoping[:create]
              scope_for_create = if action == :merge
                current_scoped_methods.create_with_value.merge(method_scoping[:create])
              else
                method_scoping[:create]
              end

              relation = relation.create_with(scope_for_create)
            else
              scope_for_create = method_scoping[:create]
              scope_for_create ||= current_scoped_methods.create_with_value if current_scoped_methods
              relation = relation.create_with(scope_for_create) if scope_for_create
            end

            method_scoping = relation
          end

          method_scoping = current_scoped_methods.merge(method_scoping) if current_scoped_methods && action ==  :merge

          self.scoped_methods << method_scoping
          begin
            yield
          ensure
            self.scoped_methods.pop
          end
        end

        # Works like with_scope, but discards any nested properties.
        def with_exclusive_scope(method_scoping = {}, &block)
          if method_scoping.values.any? { |e| e.is_a?(ActiveRecord::Relation) }
            raise ArgumentError, <<-MSG
New finder API can not be used with_exclusive_scope. You can either call unscoped to get an anonymous scope not bound to the default_scope:

  User.unscoped.where(:active => true)

Or call unscoped with a block:

  User.unscoped do
    User.where(:active => true).all
  end

MSG
          end
          with_scope(method_scoping, :overwrite, &block)
        end

        # Sets the default options for the model. The format of the
        # <tt>options</tt> argument is the same as in find.
        #
        #   class Person < ActiveRecord::Base
        #     default_scope order('last_name, first_name')
        #   end
        def default_scope(options = {})
          self.default_scoping << construct_finder_arel(options, default_scoping.pop)
        end

        def current_scoped_methods #:nodoc:
          scoped_methods.last
        end

        # Returns the class type of the record using the current module as a prefix. So descendants of
        # MyApp::Business::Account would appear as MyApp::Business::AccountSubclass.
        def compute_type(type_name)
          if type_name.match(/^::/)
            # If the type is prefixed with a scope operator then we assume that
            # the type_name is an absolute reference.
            type_name.constantize
          else
            # Build a list of candidates to search for
            candidates = []
            name.scan(/::|$/) { candidates.unshift "#{$`}::#{type_name}" }
            candidates << type_name

            candidates.each do |candidate|
              begin
                constant = candidate.constantize
                return constant if candidate == constant.to_s
              rescue NameError => e
                # We don't want to swallow NoMethodError < NameError errors
                raise e unless e.instance_of?(NameError)
              rescue ArgumentError
              end
            end

            raise NameError, "uninitialized constant #{candidates.first}"
          end
        end

        # Returns the class descending directly from ActiveRecord::Base or an
        # abstract class, if any, in the inheritance hierarchy.
        def class_of_active_record_descendant(klass)
          if klass.superclass == Base || klass.superclass.abstract_class?
            klass
          elsif klass.superclass.nil?
            raise ActiveRecordError, "#{name} doesn't belong in a hierarchy descending from ActiveRecord"
          else
            class_of_active_record_descendant(klass.superclass)
          end
        end

        # Returns the name of the class descending directly from Active Record in the inheritance hierarchy.
        def class_name_of_active_record_descendant(klass) #:nodoc:
          klass.base_class.name
        end

        # Accepts an array, hash, or string of SQL conditions and sanitizes
        # them into a valid SQL fragment for a WHERE clause.
        #   ["name='%s' and group_id='%s'", "foo'bar", 4]  returns  "name='foo''bar' and group_id='4'"
        #   { :name => "foo'bar", :group_id => 4 }  returns "name='foo''bar' and group_id='4'"
        #   "name='foo''bar' and group_id='4'" returns "name='foo''bar' and group_id='4'"
        def sanitize_sql_for_conditions(condition, table_name = self.table_name)
          return nil if condition.blank?

          case condition
            when Array; sanitize_sql_array(condition)
            when Hash;  sanitize_sql_hash_for_conditions(condition, table_name)
            else        condition
          end
        end
        alias_method :sanitize_sql, :sanitize_sql_for_conditions

        # Accepts an array, hash, or string of SQL conditions and sanitizes
        # them into a valid SQL fragment for a SET clause.
        #   { :name => nil, :group_id => 4 }  returns "name = NULL , group_id='4'"
        def sanitize_sql_for_assignment(assignments)
          case assignments
            when Array; sanitize_sql_array(assignments)
            when Hash;  sanitize_sql_hash_for_assignment(assignments)
            else        assignments
          end
        end

        def aggregate_mapping(reflection)
          mapping = reflection.options[:mapping] || [reflection.name, reflection.name]
          mapping.first.is_a?(Array) ? mapping : [mapping]
        end

        # Accepts a hash of SQL conditions and replaces those attributes
        # that correspond to a +composed_of+ relationship with their expanded
        # aggregate attribute values.
        # Given:
        #     class Person < ActiveRecord::Base
        #       composed_of :address, :class_name => "Address",
        #         :mapping => [%w(address_street street), %w(address_city city)]
        #     end
        # Then:
        #     { :address => Address.new("813 abc st.", "chicago") }
        #       # => { :address_street => "813 abc st.", :address_city => "chicago" }
        def expand_hash_conditions_for_aggregates(attrs)
          expanded_attrs = {}
          attrs.each do |attr, value|
            unless (aggregation = reflect_on_aggregation(attr.to_sym)).nil?
              mapping = aggregate_mapping(aggregation)
              mapping.each do |field_attr, aggregate_attr|
                if mapping.size == 1 && !value.respond_to?(aggregate_attr)
                  expanded_attrs[field_attr] = value
                else
                  expanded_attrs[field_attr] = value.send(aggregate_attr)
                end
              end
            else
              expanded_attrs[attr] = value
            end
          end
          expanded_attrs
        end

        # Sanitizes a hash of attribute/value pairs into SQL conditions for a WHERE clause.
        #   { :name => "foo'bar", :group_id => 4 }
        #     # => "name='foo''bar' and group_id= 4"
        #   { :status => nil, :group_id => [1,2,3] }
        #     # => "status IS NULL and group_id IN (1,2,3)"
        #   { :age => 13..18 }
        #     # => "age BETWEEN 13 AND 18"
        #   { 'other_records.id' => 7 }
        #     # => "`other_records`.`id` = 7"
        #   { :other_records => { :id => 7 } }
        #     # => "`other_records`.`id` = 7"
        # And for value objects on a composed_of relationship:
        #   { :address => Address.new("123 abc st.", "chicago") }
        #     # => "address_street='123 abc st.' and address_city='chicago'"
        def sanitize_sql_hash_for_conditions(attrs, default_table_name = self.table_name)
          attrs = expand_hash_conditions_for_aggregates(attrs)

          table = Arel::Table.new(self.table_name, :engine => arel_engine, :as => default_table_name)
          builder = PredicateBuilder.new(arel_engine)
          builder.build_from_hash(attrs, table).map(&:to_sql).join(' AND ')
        end
        alias_method :sanitize_sql_hash, :sanitize_sql_hash_for_conditions

        # Sanitizes a hash of attribute/value pairs into SQL conditions for a SET clause.
        #   { :status => nil, :group_id => 1 }
        #     # => "status = NULL , group_id = 1"
        def sanitize_sql_hash_for_assignment(attrs)
          attrs.map do |attr, value|
            "#{connection.quote_column_name(attr)} = #{quote_bound_value(value)}"
          end.join(', ')
        end

        # Accepts an array of conditions.  The array has each value
        # sanitized and interpolated into the SQL statement.
        #   ["name='%s' and group_id='%s'", "foo'bar", 4]  returns  "name='foo''bar' and group_id='4'"
        def sanitize_sql_array(ary)
          statement, *values = ary
          if values.first.is_a?(Hash) and statement =~ /:\w+/
            replace_named_bind_variables(statement, values.first)
          elsif statement.include?('?')
            replace_bind_variables(statement, values)
          else
            statement % values.collect { |value| connection.quote_string(value.to_s) }
          end
        end

        alias_method :sanitize_conditions, :sanitize_sql

        def replace_bind_variables(statement, values) #:nodoc:
          raise_if_bind_arity_mismatch(statement, statement.count('?'), values.size)
          bound = values.dup
          c = connection
          statement.gsub('?') { quote_bound_value(bound.shift, c) }
        end

        def replace_named_bind_variables(statement, bind_vars) #:nodoc:
          statement.gsub(/(:?):([a-zA-Z]\w*)/) do
            if $1 == ':' # skip postgresql casts
              $& # return the whole match
            elsif bind_vars.include?(match = $2.to_sym)
              quote_bound_value(bind_vars[match])
            else
              raise PreparedStatementInvalid, "missing value for :#{match} in #{statement}"
            end
          end
        end

        def expand_range_bind_variables(bind_vars) #:nodoc:
          expanded = []

          bind_vars.each do |var|
            next if var.is_a?(Hash)

            if var.is_a?(Range)
              expanded << var.first
              expanded << var.last
            else
              expanded << var
            end
          end

          expanded
        end

        def quote_bound_value(value, c = connection) #:nodoc:
          if value.respond_to?(:map) && !value.acts_like?(:string)
            if value.respond_to?(:empty?) && value.empty?
              c.quote(nil)
            else
              value.map { |v| c.quote(v) }.join(',')
            end
          else
            c.quote(value)
          end
        end

        def raise_if_bind_arity_mismatch(statement, expected, provided) #:nodoc:
          unless expected == provided
            raise PreparedStatementInvalid, "wrong number of bind variables (#{provided} for #{expected}) in: #{statement}"
          end
        end

        def encode_quoted_value(value) #:nodoc:
          quoted_value = connection.quote(value)
          quoted_value = "'#{quoted_value[1..-2].gsub(/\'/, "\\\\'")}'" if quoted_value.include?("\\\'") # (for ruby mode) "
          quoted_value
        end
    end

    public
      # New objects can be instantiated as either empty (pass no construction parameter) or pre-set with
      # attributes but not yet saved (pass a hash with key names matching the associated table column names).
      # In both instances, valid attribute keys are determined by the column names of the associated table --
      # hence you can't have attributes that aren't part of the table columns.
      def initialize(attributes = nil)
        @attributes = attributes_from_column_definition
        @attributes_cache = {}
        @new_record = true
        @readonly = false
        @destroyed = false
        @marked_for_destruction = false
        @previously_changed = {}
        @changed_attributes = {}

        ensure_proper_type

        if scope = self.class.send(:current_scoped_methods)
          create_with = scope.scope_for_create
          create_with.each { |att,value| self.send("#{att}=", value) } if create_with
        end
        self.attributes = attributes unless attributes.nil?

        result = yield self if block_given?
        _run_initialize_callbacks
        result
      end

      # Cloned objects have no id assigned and are treated as new records. Note that this is a "shallow" clone
      # as it copies the object's attributes only, not its associations. The extent of a "deep" clone is
      # application specific and is therefore left to the application to implement according to its need.
      def initialize_copy(other)
        callback(:after_initialize) if respond_to_without_attributes?(:after_initialize)
        cloned_attributes = other.clone_attributes(:read_attribute_before_type_cast)
        cloned_attributes.delete(self.class.primary_key)

        @attributes = cloned_attributes

        @changed_attributes = {}
        attributes_from_column_definition.each do |attr, orig_value|
          @changed_attributes[attr] = orig_value if field_changed?(attr, orig_value, @attributes[attr])
        end

        clear_aggregation_cache
        clear_association_cache
        @attributes_cache = {}
        @new_record = true
        ensure_proper_type

        if scope = self.class.send(:current_scoped_methods)
          create_with = scope.scope_for_create
          create_with.each { |att,value| self.send("#{att}=", value) } if create_with
        end
      end

      # Returns a String, which Action Pack uses for constructing an URL to this
      # object. The default implementation returns this record's id as a String,
      # or nil if this record's unsaved.
      #
      # For example, suppose that you have a User model, and that you have a
      # <tt>resources :users</tt> route. Normally, +user_path+ will
      # construct a path with the user object's 'id' in it:
      #
      #   user = User.find_by_name('Phusion')
      #   user_path(user)  # => "/users/1"
      #
      # You can override +to_param+ in your model to make +user_path+ construct
      # a path using the user's name instead of the user's id:
      #
      #   class User < ActiveRecord::Base
      #     def to_param  # overridden
      #       name
      #     end
      #   end
      #
      #   user = User.find_by_name('Phusion')
      #   user_path(user)  # => "/users/Phusion"
      def to_param
        # We can't use alias_method here, because method 'id' optimizes itself on the fly.
        id && id.to_s # Be sure to stringify the id for routes
      end

      # Returns a cache key that can be used to identify this record.
      #
      # ==== Examples
      #
      #   Product.new.cache_key     # => "products/new"
      #   Product.find(5).cache_key # => "products/5" (updated_at not available)
      #   Person.find(5).cache_key  # => "people/5-20071224150000" (updated_at available)
      def cache_key
        case
        when new_record?
          "#{self.class.model_name.cache_key}/new"
        when timestamp = self[:updated_at]
          "#{self.class.model_name.cache_key}/#{id}-#{timestamp.to_s(:number)}"
        else
          "#{self.class.model_name.cache_key}/#{id}"
        end
      end

      def quoted_id #:nodoc:
        quote_value(id, column_for_attribute(self.class.primary_key))
      end

      # Returns true if the given attribute is in the attributes hash
      def has_attribute?(attr_name)
        @attributes.has_key?(attr_name.to_s)
      end

      # Returns an array of names for the attributes available on this object sorted alphabetically.
      def attribute_names
        @attributes.keys.sort
      end

      # Returns the value of the attribute identified by <tt>attr_name</tt> after it has been typecast (for example,
      # "2004-12-12" in a data column is cast to a date object, like Date.new(2004, 12, 12)).
      # (Alias for the protected read_attribute method).
      def [](attr_name)
        read_attribute(attr_name)
      end

      # Updates the attribute identified by <tt>attr_name</tt> with the specified +value+.
      # (Alias for the protected write_attribute method).
      def []=(attr_name, value)
        write_attribute(attr_name, value)
      end

      # Allows you to set all the attributes at once by passing in a hash with keys
      # matching the attribute names (which again matches the column names).
      #
      # If +guard_protected_attributes+ is true (the default), then sensitive
      # attributes can be protected from this form of mass-assignment by using
      # the +attr_protected+ macro. Or you can alternatively specify which
      # attributes *can* be accessed with the +attr_accessible+ macro. Then all the
      # attributes not included in that won't be allowed to be mass-assigned.
      #
      #   class User < ActiveRecord::Base
      #     attr_protected :is_admin
      #   end
      #
      #   user = User.new
      #   user.attributes = { :username => 'Phusion', :is_admin => true }
      #   user.username   # => "Phusion"
      #   user.is_admin?  # => false
      #
      #   user.send(:attributes=, { :username => 'Phusion', :is_admin => true }, false)
      #   user.is_admin?  # => true
      def attributes=(new_attributes, guard_protected_attributes = true)
        return if new_attributes.nil?
        attributes = new_attributes.stringify_keys

        multi_parameter_attributes = []
        attributes = remove_attributes_protected_from_mass_assignment(attributes) if guard_protected_attributes

        attributes.each do |k, v|
          if k.include?("(")
            multi_parameter_attributes << [ k, v ]
          else
            respond_to?(:"#{k}=") ? send(:"#{k}=", v) : raise(UnknownAttributeError, "unknown attribute: #{k}")
          end
        end

        assign_multiparameter_attributes(multi_parameter_attributes)
      end

      # Returns a hash of all the attributes with their names as keys and the values of the attributes as values.
      def attributes
        attrs = {}
        attribute_names.each { |name| attrs[name] = read_attribute(name) }
        attrs
      end

      # Returns an <tt>#inspect</tt>-like string for the value of the
      # attribute +attr_name+. String attributes are elided after 50
      # characters, and Date and Time attributes are returned in the
      # <tt>:db</tt> format. Other attributes return the value of
      # <tt>#inspect</tt> without modification.
      #
      #   person = Person.create!(:name => "David Heinemeier Hansson " * 3)
      #
      #   person.attribute_for_inspect(:name)
      #   # => '"David Heinemeier Hansson David Heinemeier Hansson D..."'
      #
      #   person.attribute_for_inspect(:created_at)
      #   # => '"2009-01-12 04:48:57"'
      def attribute_for_inspect(attr_name)
        value = read_attribute(attr_name)

        if value.is_a?(String) && value.length > 50
          "#{value[0..50]}...".inspect
        elsif value.is_a?(Date) || value.is_a?(Time)
          %("#{value.to_s(:db)}")
        else
          value.inspect
        end
      end

      # Returns true if the specified +attribute+ has been set by the user or by a database load and is neither
      # nil nor empty? (the latter only applies to objects that respond to empty?, most notably Strings).
      def attribute_present?(attribute)
        value = read_attribute(attribute)
        !value.blank?
      end

      # Returns the column object for the named attribute.
      def column_for_attribute(name)
        self.class.columns_hash[name.to_s]
      end

      # Returns true if the +comparison_object+ is the same object, or is of the same type and has the same id.
      def ==(comparison_object)
        comparison_object.equal?(self) ||
          (comparison_object.instance_of?(self.class) &&
            comparison_object.id == id && !comparison_object.new_record?)
      end

      # Delegates to ==
      def eql?(comparison_object)
        self == (comparison_object)
      end

      # Delegates to id in order to allow two records of the same type and id to work with something like:
      #   [ Person.find(1), Person.find(2), Person.find(3) ] & [ Person.find(1), Person.find(4) ] # => [ Person.find(1) ]
      def hash
        id.hash
      end

      # Freeze the attributes hash such that associations are still accessible, even on destroyed records.
      def freeze
        @attributes.freeze; self
      end

      # Returns +true+ if the attributes hash has been frozen.
      def frozen?
        @attributes.frozen?
      end

      # Returns duplicated record with unfreezed attributes.
      def dup
        obj = super
        obj.instance_variable_set('@attributes', @attributes.dup)
        obj
      end

      # Returns +true+ if the record is read only. Records loaded through joins with piggy-back
      # attributes will be marked as read only since they cannot be saved.
      def readonly?
        @readonly
      end

      # Marks this record as read only.
      def readonly!
        @readonly = true
      end

      # Returns the contents of the record as a nicely formatted string.
      def inspect
        attributes_as_nice_string = self.class.column_names.collect { |name|
          if has_attribute?(name) || new_record?
            "#{name}: #{attribute_for_inspect(name)}"
          end
        }.compact.join(", ")
        "#<#{self.class} #{attributes_as_nice_string}>"
      end

    protected
      def clone_attributes(reader_method = :read_attribute, attributes = {})
        attribute_names.each do |name|
          attributes[name] = clone_attribute_value(reader_method, name)
        end
        attributes
      end

      def clone_attribute_value(reader_method, attribute_name)
        value = send(reader_method, attribute_name)
        value.duplicable? ? value.clone : value
      rescue TypeError, NoMethodError
        value
      end

    private

      # Sets the attribute used for single table inheritance to this class name if this is not the ActiveRecord::Base descendant.
      # Considering the hierarchy Reply < Message < ActiveRecord::Base, this makes it possible to do Reply.new without having to
      # set <tt>Reply[Reply.inheritance_column] = "Reply"</tt> yourself. No such attribute would be set for objects of the
      # Message class in that example.
      def ensure_proper_type
        unless self.class.descends_from_active_record?
          write_attribute(self.class.inheritance_column, self.class.sti_name)
        end
      end

      def remove_attributes_protected_from_mass_assignment(attributes)
        safe_attributes =
          if self.class.accessible_attributes.nil? && self.class.protected_attributes.nil?
            attributes.reject { |key, value| attributes_protected_by_default.include?(key.gsub(/\(.+/, "")) }
          elsif self.class.protected_attributes.nil?
            attributes.reject { |key, value| !self.class.accessible_attributes.include?(key.gsub(/\(.+/, "")) || attributes_protected_by_default.include?(key.gsub(/\(.+/, "")) }
          elsif self.class.accessible_attributes.nil?
            attributes.reject { |key, value| self.class.protected_attributes.include?(key.gsub(/\(.+/,"")) || attributes_protected_by_default.include?(key.gsub(/\(.+/, "")) }
          else
            raise "Declare either attr_protected or attr_accessible for #{self.class}, but not both."
          end

        removed_attributes = attributes.keys - safe_attributes.keys

        if removed_attributes.any?
          log_protected_attribute_removal(removed_attributes)
        end

        safe_attributes
      end

      # Removes attributes which have been marked as readonly.
      def remove_readonly_attributes(attributes)
        unless self.class.readonly_attributes.nil?
          attributes.delete_if { |key, value| self.class.readonly_attributes.include?(key.gsub(/\(.+/,"")) }
        else
          attributes
        end
      end

      def log_protected_attribute_removal(*attributes)
        if logger
          logger.debug "WARNING: Can't mass-assign these protected attributes: #{attributes.join(', ')}"
        end
      end

      # The primary key and inheritance column can never be set by mass-assignment for security reasons.
      def attributes_protected_by_default
        default = [ self.class.primary_key, self.class.inheritance_column ]
        default << 'id' unless self.class.primary_key.eql? 'id'
        default
      end

      # Returns a copy of the attributes hash where all the values have been safely quoted for use in
      # an Arel insert/update method.
      def arel_attributes_values(include_primary_key = true, include_readonly_attributes = true, attribute_names = @attributes.keys)
        attrs = {}
        attribute_names.each do |name|
          if (column = column_for_attribute(name)) && (include_primary_key || !column.primary)

            if include_readonly_attributes || (!include_readonly_attributes && !self.class.readonly_attributes.include?(name))
              value = read_attribute(name)

              if value && ((self.class.serialized_attributes.has_key?(name) && (value.acts_like?(:date) || value.acts_like?(:time))) || value.is_a?(Hash) || value.is_a?(Array))
                value = value.to_yaml
              end
              attrs[self.class.arel_table[name]] = value
            end
          end
        end
        attrs
      end

      # Quote strings appropriately for SQL statements.
      def quote_value(value, column = nil)
        self.class.connection.quote(value, column)
      end

      # Interpolate custom SQL string in instance context.
      # Optional record argument is meant for custom insert_sql.
      def interpolate_sql(sql, record = nil)
        instance_eval("%@#{sql.gsub('@', '\@')}@", __FILE__, __LINE__)
      end

      # Instantiates objects for all attribute classes that needs more than one constructor parameter. This is done
      # by calling new on the column type or aggregation type (through composed_of) object with these parameters.
      # So having the pairs written_on(1) = "2004", written_on(2) = "6", written_on(3) = "24", will instantiate
      # written_on (a date type) with Date.new("2004", "6", "24"). You can also specify a typecast character in the
      # parentheses to have the parameters typecasted before they're used in the constructor. Use i for Fixnum, f for Float,
      # s for String, and a for Array. If all the values for a given attribute are empty, the attribute will be set to nil.
      def assign_multiparameter_attributes(pairs)
        execute_callstack_for_multiparameter_attributes(
          extract_callstack_for_multiparameter_attributes(pairs)
        )
      end

      def instantiate_time_object(name, values)
        if self.class.send(:create_time_zone_conversion_attribute?, name, column_for_attribute(name))
          Time.zone.local(*values)
        else
          Time.time_with_datetime_fallback(@@default_timezone, *values)
        end
      end

      def execute_callstack_for_multiparameter_attributes(callstack)
        errors = []
        callstack.each do |name, values_with_empty_parameters|
          begin
            klass = (self.class.reflect_on_aggregation(name.to_sym) || column_for_attribute(name)).klass
            # in order to allow a date to be set without a year, we must keep the empty values.
            # Otherwise, we wouldn't be able to distinguish it from a date with an empty day.
            values = values_with_empty_parameters.reject(&:nil?)

            if values.empty?
              send(name + "=", nil)
            else

              value = if Time == klass
                instantiate_time_object(name, values)
              elsif Date == klass
                begin
                  values = values_with_empty_parameters.collect do |v| v.nil? ? 1 : v end
                  Date.new(*values)
                rescue ArgumentError => ex # if Date.new raises an exception on an invalid date
                  instantiate_time_object(name, values).to_date # we instantiate Time object and convert it back to a date thus using Time's logic in handling invalid dates
                end
              else
                klass.new(*values)
              end

              send(name + "=", value)
            end
          rescue => ex
            errors << AttributeAssignmentError.new("error on assignment #{values.inspect} to #{name}", ex, name)
          end
        end
        unless errors.empty?
          raise MultiparameterAssignmentErrors.new(errors), "#{errors.size} error(s) on assignment of multiparameter attributes"
        end
      end

      def extract_callstack_for_multiparameter_attributes(pairs)
        attributes = { }

        for pair in pairs
          multiparameter_name, value = pair
          attribute_name = multiparameter_name.split("(").first
          attributes[attribute_name] = [] unless attributes.include?(attribute_name)

          parameter_value = value.empty? ? nil : type_cast_attribute_value(multiparameter_name, value)
          attributes[attribute_name] << [ find_parameter_position(multiparameter_name), parameter_value ]
        end

        attributes.each { |name, values| attributes[name] = values.sort_by{ |v| v.first }.collect { |v| v.last } }
      end

      def type_cast_attribute_value(multiparameter_name, value)
        multiparameter_name =~ /\([0-9]*([if])\)/ ? value.send("to_" + $1) : value
      end

      def find_parameter_position(multiparameter_name)
        multiparameter_name.scan(/\(([0-9]*).*\)/).first.first
      end

      # Returns a comma-separated pair list, like "key1 = val1, key2 = val2".
      def comma_pair_list(hash)
        hash.map { |k,v| "#{k} = #{v}" }.join(", ")
      end

      def quote_columns(quoter, hash)
        hash.inject({}) do |quoted, (name, value)|
          quoted[quoter.quote_column_name(name)] = value
          quoted
        end
      end

      def quoted_comma_pair_list(quoter, hash)
        comma_pair_list(quote_columns(quoter, hash))
      end

      def convert_number_column_value(value)
        if value == false
          0
        elsif value == true
          1
        elsif value.is_a?(String) && value.blank?
          nil
        else
          value
        end
      end

      def object_from_yaml(string)
        return string unless string.is_a?(String) && string =~ /^---/
        YAML::load(string) rescue string
      end
  end

  Base.class_eval do
    include ActiveRecord::Persistence
    extend ActiveModel::Naming
    extend QueryCache::ClassMethods
    extend ActiveSupport::Benchmarkable
    extend ActiveSupport::DescendantsTracker

    include ActiveModel::Conversion
    include Validations
    extend CounterCache
    include Locking::Optimistic, Locking::Pessimistic
    include AttributeMethods
    include AttributeMethods::Read, AttributeMethods::Write, AttributeMethods::BeforeTypeCast, AttributeMethods::Query
    include AttributeMethods::PrimaryKey
    include AttributeMethods::TimeZoneConversion
    include AttributeMethods::Dirty
    include Callbacks, ActiveModel::Observing, Timestamp
    include Associations, AssociationPreload, NamedScope

    # AutosaveAssociation needs to be included before Transactions, because we want
    # #save_with_autosave_associations to be wrapped inside a transaction.
    include AutosaveAssociation, NestedAttributes
    include Aggregations, Transactions, Reflection, Serialization

    NilClass.add_whiner(self) if NilClass.respond_to?(:add_whiner)
  end
end

# TODO: Remove this and make it work with LAZY flag
require 'active_record/connection_adapters/abstract_adapter'
ActiveSupport.run_load_hooks(:active_record, ActiveRecord::Base)