Add extensive documentation to the ActiveRecord::AbstractAdapter. #2250

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@2371 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

6 files changed, 210 insertions, 38 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb
index 8b94d68717..be5be0fff4 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb
@@ -1,4 +1,5 @@
 module ActiveRecord
+  # The root class of all active record objects.
   class Base
     class ConnectionSpecification #:nodoc:
       attr_reader :config, :adapter_method
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
index 1e8dd045f6..809424c078 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -1,11 +1,12 @@
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
-    # TODO: Document me!
     module DatabaseStatements
-      # Returns an array of record hashes with the column names as a keys and fields as values.
+      # Returns an array of record hashes with the column names as keys and
+      # column values as values.
       def select_all(sql, name = nil) end
 
-      # Returns a record hash with the column names as a keys and fields as values.
+      # Returns a record hash with the column names as keys and column values
+      # as values.
       def select_one(sql, name = nil) end
 
       # Returns a single value from a record
@@ -21,8 +22,11 @@ module ActiveRecord
         result.map{ |v| v.values.first }
       end
 
-      # Executes the statement
-      def execute(sql, name = nil) end
+      # Executes the SQL statement in the context of this connection.
+      # This abstract method raises a NotImplementedError.
+      def execute(sql, name = nil)
+        raise NotImplementedError, "execute is an abstract method"
+      end
 
       # Returns the last auto-generated ID from the affected table.
       def insert(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil) end
@@ -54,16 +58,23 @@ module ActiveRecord
       # Commits the transaction (and turns on auto-committing).
       def commit_db_transaction()   end
 
-      # Rolls back the transaction (and turns on auto-committing). Must be done if the transaction block
-      # raises an exception or returns false.
+      # Rolls back the transaction (and turns on auto-committing). Must be
+      # done if the transaction block raises an exception or returns false.
       def rollback_db_transaction() end
 
-      def add_limit!(sql, options) #:nodoc:
+      # Alias for #add_limit_offset!.
+      def add_limit!(sql, options)
         return unless options
         add_limit_offset!(sql, options)
       end
 
-      def add_limit_offset!(sql, options) #:nodoc:
+      # Appends +LIMIT+ and +OFFSET+ options to a SQL statement.
+      # This method *modifies* the +sql+ parameter.
+      # ===== Examples
+      #  add_limit_offset!('SELECT * FROM suppliers', {:limit => 10, :offset => 50})
+      # generates
+      #  SELECT * FROM suppliers LIMIT 10 OFFSET 50
+      def add_limit_offset!(sql, options)
         return if options[:limit].nil?
         sql << " LIMIT #{options[:limit]}"
         sql << " OFFSET #{options[:offset]}" if options.has_key?(:offset) and !options[:offset].nil?
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb b/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb
index 7f7cc03c7a..c8088bd978 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb
@@ -1,7 +1,8 @@
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
-    # TODO: Document me!
     module Quoting
+      # Quotes the column value to help prevent
+      # {SQL injection attacks}[http://en.wikipedia.org/wiki/SQL_injection].
       def quote(value, column = nil)
         case value
           when String
@@ -22,10 +23,14 @@ module ActiveRecord
         end
       end
 
+      # Quotes a string, escaping any ' (single quote) and \ (backslash)
+      # characters.
       def quote_string(s)
         s.gsub(/\\/, '\&\&').gsub(/'/, "''") # ' (for ruby-mode)
       end
 
+      # Returns a quoted form of the column name.  This is highly adapter
+      # specific.
       def quote_column_name(name)
         name
       end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index f90ac0266a..424a898db3 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -1,11 +1,15 @@
 module ActiveRecord
   module ConnectionAdapters #:nodoc:
-    class Column #:nodoc:
+    # An abstract definition of a column in a table.
+    class Column
       attr_reader :name, :default, :type, :limit, :null
-      # The name should contain the name of the column, such as "name" in "name varchar(250)"
-      # The default should contain the type-casted default of the column, such as 1 in "count int(11) DEFAULT 1"
-      # The type parameter should either contain :integer, :float, :datetime, :date, :text, or :string
-      # The sql_type is just used for extracting the limit, such as 10 in "varchar(10)"
+
+      # Instantiates a new column in the table.
+      #
+      # +name+ is the column's name, as in <tt><b>supplier_id</b> int(11)</tt>.
+      # +default+ is the type-casted default value, such as <tt>sales_stage varchar(20) default <b>'new'</b></tt>.
+      # +sql_type+ is only used to extract the column's length, if necessary.  For example, <tt>company_name varchar(<b>60</b>)</tt>.
+      # +null+ determines if this column allows +NULL+ values.
       def initialize(name, default, sql_type = nil, null = true)
         @name, @type, @null = name, simplified_type(sql_type), null
         # have to do this one separately because type_cast depends on #type
@@ -13,6 +17,7 @@ module ActiveRecord
         @limit = extract_limit(sql_type) unless sql_type.nil?
       end
 
+      # Returns the Ruby class that corresponds to the abstract data type.
       def klass
         case type
           when :integer       then Fixnum
@@ -27,6 +32,7 @@ module ActiveRecord
         end
       end
 
+      # Casts value (which is a String) to an appropriate instance.
       def type_cast(value)
         if value.nil? then return nil end
         case type
@@ -44,14 +50,20 @@ module ActiveRecord
         end
       end
 
+      # Returns the human name of the column name.
+      #
+      # ===== Examples
+      #  Column.new('sales_stage', ...).human_name #=> 'Sales stage'
       def human_name
         Base.human_attribute_name(@name)
       end
 
+      # Used to convert from Strings to BLOBs
       def string_to_binary(value)
         value
       end
 
+      # Used to convert from BLOBs to Strings
       def binary_to_string(value)
         value
       end
@@ -108,7 +120,7 @@ module ActiveRecord
           end
         end
     end
-    
+
     class IndexDefinition < Struct.new(:table, :name, :unique, :columns) #:nodoc:
     end
 
@@ -130,7 +142,9 @@ module ActiveRecord
         end
     end
 
-    class TableDefinition #:nodoc:
+    # Represents a SQL table in an abstract way.
+    # Columns are stored as ColumnDefinition in the #columns attribute.
+    class TableDefinition
       attr_accessor :columns
 
       def initialize(base)
@@ -138,14 +152,48 @@ module ActiveRecord
         @base = base
       end
 
+      # Appends a primary key definition to the table definition.
+      # Can be called multiple times, but this is probably not a good idea.
       def primary_key(name)
         column(name, native[:primary_key])
       end
-      
+
+      # Returns a ColumnDefinition for the column with name +name+.
       def [](name)
         @columns.find {|column| column.name == name}
       end
 
+      # Instantiates a new column for the table.
+      # The +type+ parameter must be one of the following values:
+      # <tt>:primary_key</tt>, <tt>:string</tt>, <tt>:text</tt>,
+      # <tt>:integer</tt>, <tt>:float</tt>, <tt>:datetime</tt>,
+      # <tt>:timestamp</tt>, <tt>:time</tt>, <tt>:date</tt>,
+      # <tt>:binary</tt>, <tt>:boolean</tt>.
+      #
+      # Available options are (none of these exists by default):
+      # * <tt>:limit</tt>:
+      #   Requests a maximum column length (<tt>:string</tt>, <tt>:text</tt>,
+      #   <tt>:binary</tt> or <tt>:integer</tt> columns only)
+      # * <tt>:default</tt>:
+      #   The column's default value.  You cannot explicitely set the default
+      #   value to +NULL+.  Simply leave off this option if you want a +NULL+
+      #   default value.
+      # * <tt>:null</tt>:
+      #   Allows or disallows +NULL+ values in the column.  This option could
+      #   have been named <tt>:null_allowed</tt>.
+      #
+      # This method returns <tt>self</tt>.
+      #
+      # ===== Examples
+      #  # Assuming def is an instance of TableDefinition
+      #  def.column(:granted, :boolean)
+      #    #=> granted BOOLEAN
+      #
+      #  def.column(:picture, :binary, :limit => 2.megabytes)
+      #    #=> picture BLOB(2097152)
+      #
+      #  def.column(:sales_stage, :string, :limit => 20, :default => 'new', :null => false)
+      #    #=> sales_stage VARCHAR(20) DEFAULT 'new' NOT NULL
       def column(name, type, options = {})
         column = self[name] || ColumnDefinition.new(@base, name, type)
         column.limit = options[:limit] || native[type.to_sym][:limit] if options[:limit] or native[type.to_sym]
@@ -155,6 +203,9 @@ module ActiveRecord
         self
       end
             
+      # Returns a String whose contents are the column definitions
+      # concatenated together.  This string can then be pre and appended to
+      # to generate the final SQL to create the table.
       def to_sql
         @columns * ', '
       end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index d7aefc9a82..ea9173039c 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -1,8 +1,10 @@
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
-    # TODO: Document me!
     module SchemaStatements
-      def native_database_types #:nodoc:
+      # Returns a Hash of mappings from the abstract data types to the native
+      # database types.  See TableDefinition#column for details on the recognized
+      # abstract data types.
+      def native_database_types
         {}
       end
 
@@ -11,10 +13,67 @@ module ActiveRecord
       # Returns an array of indexes for the given table.
       # def indexes(table_name, name = nil) end
 
-      # Returns an array of column objects for the table specified by +table_name+.
+      # Returns an array of Column objects for the table specified by +table_name+.
+      # See the concrete implementation for details on the expected parameter values.
       def columns(table_name, name = nil) end
 
-
+      # Creates a new table
+      # There are two ways to work with #create_table.  You can use the block
+      # form or the regular form, like this:
+      #
+      # === Block form
+      #  # create_table() yields a TableDefinition instance
+      #  create_table(:suppliers) do |t|
+      #    t.column :name, :string, :limit => 60
+      #    # Other fields here
+      #  end
+      #
+      # === Regular form
+      #  create_table(:suppliers)
+      #  add_column(:suppliers, :name, :string, {:limit => 60})
+      #
+      # The +options+ hash can include the following keys:
+      # [<tt>:id</tt>]
+      #   Set to true or false to add/not add a primary key column
+      #   automatically.  Defaults to true.
+      # [<tt>:primary_key</tt>]
+      #   The name of the primary key, if one is to be added automatically.
+      #   Defaults to +id+.
+      # [<tt>:options</tt>]
+      #   Any extra options you want appended to the table definition.
+      # [<tt>:temporary</tt>]
+      #   Make a temporary table.
+      #
+      # ===== Examples
+      # ====== Add a backend specific option to the generated SQL (MySQL)
+      #  create_table(:suppliers, :options => 'ENGINE=InnoDB DEFAULT CHARSET=utf8')
+      # generates:
+      #  CREATE TABLE suppliers (
+      #    id int(11) DEFAULT NULL auto_increment PRIMARY KEY
+      #  ) ENGINE=InnoDB DEFAULT CHARSET=utf8
+      #
+      # ====== Rename the primary key column
+      #  create_table(:objects, :primary_key => 'guid') do |t|
+      #    t.column :name, :string, :limit => 80
+      #  end
+      # generates:
+      #  CREATE TABLE objects (
+      #    guid int(11) DEFAULT NULL auto_increment PRIMARY KEY,
+      #    name varchar(80)
+      #  )
+      #
+      # ====== Do not add a primary key column
+      #  create_table(:categories_suppliers, :id => false) do |t|
+      #    t.column :category_id, :integer
+      #    t.column :supplier_id, :integer
+      #  end
+      # generates:
+      #  CREATE TABLE categories_suppliers_join (
+      #    category_id int,
+      #    supplier_id int
+      #  )
+      #
+      # See also TableDefinition#column for details on how to create columns.
       def create_table(name, options = {})
         table_definition = TableDefinition.new(self)
         table_definition.primary_key(options[:primary_key] || "id") unless options[:id] == false
@@ -27,37 +86,71 @@ module ActiveRecord
         execute create_sql
       end
 
+      # Drops a table from the database.
       def drop_table(name)
         execute "DROP TABLE #{name}"
       end
 
+      # Adds a new column to the named table.
+      # See TableDefinition#column for details of the options you can use.
       def add_column(table_name, column_name, type, options = {})
         add_column_sql = "ALTER TABLE #{table_name} ADD #{column_name} #{type_to_sql(type, options[:limit])}"
         add_column_options!(add_column_sql, options)
         execute(add_column_sql)
       end
 
+      # Removes the column from the table definition.
+      # ===== Examples
+      #  remove_column(:suppliers, :qualification)
       def remove_column(table_name, column_name)
         execute "ALTER TABLE #{table_name} DROP #{column_name}"
       end      
 
+      # Changes the column's definition according to the new options.
+      # See TableDefinition#column for details of the options you can use.
+      # ===== Examples
+      #  change_column(:suppliers, :name, :string, :limit => 80)
+      #  change_column(:accounts, :description, :text)
       def change_column(table_name, column_name, type, options = {})
         raise NotImplementedError, "change_column is not implemented"
       end
 
+      # Sets a new default value for a column.  If you want to set the default
+      # value to +NULL+, you are out of luck.  You need to
+      # DatabaseStatements#execute the apppropriate SQL statement yourself.
+      # ===== Examples
+      #  change_column_default(:suppliers, :qualification, 'new')
+      #  change_column_default(:accounts, :authorized, 1)
       def change_column_default(table_name, column_name, default)
         raise NotImplementedError, "change_column_default is not implemented"
       end
 
+      # Renames a column.
+      # ===== Example
+      #  rename_column(:suppliers, :description, :name)
       def rename_column(table_name, column_name, new_column_name)
         raise NotImplementedError, "rename_column is not implemented"
       end
 
-      # Create a new index on the given table. By default, it will be named
-      # <code>"#{table_name}_#{Array(column_name).first}_index"</code>, but you
-      # can explicitly name the index by passing <code>:name => "..."</code>
-      # as the last parameter. Unique indexes may be created by passing
-      # <code>:unique => true</code>.
+      # Adds a new index to the table.  +column_name+ can be a single Symbol, or
+      # an Array of Symbols.
+      #
+      # The index will be named after the table and the first column names,
+      # unless you pass +:name+ as an option.
+      #
+      # ===== Examples
+      # ====== Creating a simple index
+      #  add_index(:suppliers, :name)
+      # generates
+      #  CREATE INDEX suppliers_name_index ON suppliers(name)
+      # ====== Creating a unique index
+      #  add_index(:accounts, [:branch_id, :party_id], :unique => true)
+      # generates
+      #  CREATE UNIQUE INDEX accounts_branch_id_index ON accounts(branch_id, party_id)
+      # ====== Creating a named index
+      #  add_index(:accounts, [:branch_id, :party_id], :unique => true, :name => 'by_branch_party')
+      # generates
+      #  CREATE UNIQUE INDEX by_branch_party ON accounts(branch_id, party_id)
       def add_index(table_name, column_name, options = {})
         index_name = "#{table_name}_#{Array(column_name).first}_index"
 
@@ -73,12 +166,12 @@ module ActiveRecord
 
       # Remove the given index from the table.
       #
-      #   remove_index :my_table, :column => :foo
-      #   remove_index :my_table, :name => :my_index_on_foo
-      #
-      # The first version will remove the index named
-      # <code>"#{my_table}_#{column}_index"</code> from the table. The
-      # second removes the named column from the table.
+      # Remove the suppliers_name_index in the suppliers table (legacy support, use the second or third forms).
+      #   remove_index :suppliers, :name
+      # Remove the index named accounts_branch_id in the accounts table.
+      #   remove_index :accounts, :column => :branch_id
+      # Remove the index named by_branch_party in the accounts table.
+      #   remove_index :accounts, :name => :by_branch_party
       def remove_index(table_name, options = {})
         if Hash === options # legacy support
           if options[:column]
@@ -96,11 +189,14 @@ module ActiveRecord
       end
 
 
-      # Returns a string of the CREATE TABLE SQL statements for recreating the entire structure of the database.
-      def structure_dump #:nodoc:
+      # Returns a string of <tt>CREATE TABLE</tt> SQL statement(s) for recreating the
+      # entire structure of the database.
+      def structure_dump
       end
 
-      def initialize_schema_information #:nodoc:
+      # Should not be called normally, but this operation is non-destructive.
+      # The migrations module handles this automatically.
+      def initialize_schema_information
         begin
           execute "CREATE TABLE #{ActiveRecord::Migrator.schema_info_table_name} (version #{type_to_sql(:integer)})"
           execute "INSERT INTO #{ActiveRecord::Migrator.schema_info_table_name} (version) VALUES(0)"
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index f6dfc4bfd4..a028cdbc00 100755
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -35,6 +35,12 @@ module ActiveRecord
     # All the concrete database adapters follow the interface laid down in this class.
     # You can use this interface directly by borrowing the database connection from the Base with
     # Base.connection.
+    #
+    # Most of the methods in the adapter are useful during migrations.  Most
+    # notably, SchemaStatements#create_table, SchemaStatements#drop_table,
+    # SchemaStatements#add_index, SchemaStatements#remove_index,
+    # SchemaStatements#add_column, SchemaStatements#change_column and
+    # SchemaStatements#remove_column are very useful.
     class AbstractAdapter
       include Quoting, DatabaseStatements, SchemaStatements
       @@row_even = true
@@ -44,12 +50,14 @@ module ActiveRecord
         @runtime = 0
       end
 
-      # Returns the human-readable name of the adapter.  Use mixed case - one can always use downcase if needed.
+      # Returns the human-readable name of the adapter.  Use mixed case - one
+      # can always use downcase if needed.
       def adapter_name
         'Abstract'
       end
       
-      # Returns true for database adapters that has implemented the schema statements.
+      # Does this adapter support migrations ?  Backend specific, as the
+      # abstract adapter always returns +false+.
       def supports_migrations?
         false
       end