require 'active_support/core_ext/enumerable' require 'active_support/core_ext/string/conversions' require 'active_support/core_ext/module/remove_method' require 'active_record/errors' module ActiveRecord class InverseOfAssociationNotFoundError < ActiveRecordError #:nodoc: def initialize(reflection, associated_class = nil) super("Could not find the inverse association for #{reflection.name} (#{reflection.options[:inverse_of].inspect} in #{associated_class.nil? ? reflection.class_name : associated_class.name})") end end class HasManyThroughAssociationNotFoundError < ActiveRecordError #:nodoc: def initialize(owner_class_name, reflection) super("Could not find the association #{reflection.options[:through].inspect} in model #{owner_class_name}") end end class HasManyThroughAssociationPolymorphicSourceError < ActiveRecordError #:nodoc: def initialize(owner_class_name, reflection, source_reflection) super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' on the polymorphic object '#{source_reflection.class_name}##{source_reflection.name}' without 'source_type'. Try adding 'source_type: \"#{reflection.name.to_s.classify}\"' to 'has_many :through' definition.") end end class HasManyThroughAssociationPolymorphicThroughError < ActiveRecordError #:nodoc: def initialize(owner_class_name, reflection) super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' which goes through the polymorphic association '#{owner_class_name}##{reflection.through_reflection.name}'.") end end class HasManyThroughAssociationPointlessSourceTypeError < ActiveRecordError #:nodoc: def initialize(owner_class_name, reflection, source_reflection) super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' with a :source_type option if the '#{reflection.through_reflection.class_name}##{source_reflection.name}' is not polymorphic. Try removing :source_type on your association.") end end class HasOneThroughCantAssociateThroughCollection < ActiveRecordError #:nodoc: def initialize(owner_class_name, reflection, through_reflection) super("Cannot have a has_one :through association '#{owner_class_name}##{reflection.name}' where the :through association '#{owner_class_name}##{through_reflection.name}' is a collection. Specify a has_one or belongs_to association in the :through option instead.") end end class HasManyThroughSourceAssociationNotFoundError < ActiveRecordError #:nodoc: def initialize(reflection) through_reflection = reflection.through_reflection source_reflection_names = reflection.source_reflection_names source_associations = reflection.through_reflection.klass.reflect_on_all_associations.collect { |a| a.name.inspect } super("Could not find the source association(s) #{source_reflection_names.collect{ |a| a.inspect }.to_sentence(:two_words_connector => ' or ', :last_word_connector => ', or ', :locale => :en)} in model #{through_reflection.klass}. Try 'has_many #{reflection.name.inspect}, :through => #{through_reflection.name.inspect}, :source => <name>'. Is it one of #{source_associations.to_sentence(:two_words_connector => ' or ', :last_word_connector => ', or ', :locale => :en)}?") end end class HasManyThroughCantAssociateThroughHasOneOrManyReflection < ActiveRecordError #:nodoc: def initialize(owner, reflection) super("Cannot modify association '#{owner.class.name}##{reflection.name}' because the source reflection class '#{reflection.source_reflection.class_name}' is associated to '#{reflection.through_reflection.class_name}' via :#{reflection.source_reflection.macro}.") end end class HasManyThroughCantAssociateNewRecords < ActiveRecordError #:nodoc: def initialize(owner, reflection) super("Cannot associate new records through '#{owner.class.name}##{reflection.name}' on '#{reflection.source_reflection.class_name rescue nil}##{reflection.source_reflection.name rescue nil}'. Both records must have an id in order to create the has_many :through record associating them.") end end class HasManyThroughCantDissociateNewRecords < ActiveRecordError #:nodoc: def initialize(owner, reflection) super("Cannot dissociate new records through '#{owner.class.name}##{reflection.name}' on '#{reflection.source_reflection.class_name rescue nil}##{reflection.source_reflection.name rescue nil}'. Both records must have an id in order to delete the has_many :through record associating them.") end end class HasManyThroughNestedAssociationsAreReadonly < ActiveRecordError #:nodoc: def initialize(owner, reflection) super("Cannot modify association '#{owner.class.name}##{reflection.name}' because it goes through more than one other association.") end end class HasAndBelongsToManyAssociationForeignKeyNeeded < ActiveRecordError #:nodoc: def initialize(reflection) super("Cannot create self referential has_and_belongs_to_many association on '#{reflection.class_name rescue nil}##{reflection.name rescue nil}'. :association_foreign_key cannot be the same as the :foreign_key.") end end class EagerLoadPolymorphicError < ActiveRecordError #:nodoc: def initialize(reflection) super("Can not eagerly load the polymorphic association #{reflection.name.inspect}") end end class ReadOnlyAssociation < ActiveRecordError #:nodoc: def initialize(reflection) super("Can not add to a has_many :through association. Try adding to #{reflection.through_reflection.name.inspect}.") end end # This error is raised when trying to destroy a parent instance in N:1 or 1:1 associations # (has_many, has_one) when there is at least 1 child associated instance. # ex: if @project.tasks.size > 0, DeleteRestrictionError will be raised when trying to destroy @project class DeleteRestrictionError < ActiveRecordError #:nodoc: def initialize(name) super("Cannot delete record because of dependent #{name}") end end # See ActiveRecord::Associations::ClassMethods for documentation. module Associations # :nodoc: extend ActiveSupport::Autoload extend ActiveSupport::Concern # These classes will be loaded when associations are created. # So there is no need to eager load them. autoload :Association, 'active_record/associations/association' autoload :SingularAssociation, 'active_record/associations/singular_association' autoload :CollectionAssociation, 'active_record/associations/collection_association' autoload :CollectionProxy, 'active_record/associations/collection_proxy' autoload :BelongsToAssociation, 'active_record/associations/belongs_to_association' autoload :BelongsToPolymorphicAssociation, 'active_record/associations/belongs_to_polymorphic_association' autoload :HasAndBelongsToManyAssociation, 'active_record/associations/has_and_belongs_to_many_association' autoload :HasManyAssociation, 'active_record/associations/has_many_association' autoload :HasManyThroughAssociation, 'active_record/associations/has_many_through_association' autoload :HasOneAssociation, 'active_record/associations/has_one_association' autoload :HasOneThroughAssociation, 'active_record/associations/has_one_through_association' autoload :ThroughAssociation, 'active_record/associations/through_association' module Builder #:nodoc: autoload :Association, 'active_record/associations/builder/association' autoload :SingularAssociation, 'active_record/associations/builder/singular_association' autoload :CollectionAssociation, 'active_record/associations/builder/collection_association' autoload :BelongsTo, 'active_record/associations/builder/belongs_to' autoload :HasOne, 'active_record/associations/builder/has_one' autoload :HasMany, 'active_record/associations/builder/has_many' autoload :HasAndBelongsToMany, 'active_record/associations/builder/has_and_belongs_to_many' end eager_autoload do autoload :Preloader, 'active_record/associations/preloader' autoload :JoinDependency, 'active_record/associations/join_dependency' autoload :AssociationScope, 'active_record/associations/association_scope' autoload :AliasTracker, 'active_record/associations/alias_tracker' autoload :JoinHelper, 'active_record/associations/join_helper' end # Clears out the association cache. def clear_association_cache #:nodoc: @association_cache.clear if persisted? end # :nodoc: attr_reader :association_cache # Returns the association instance for the given name, instantiating it if it doesn't already exist def association(name) #:nodoc: association = association_instance_get(name) if association.nil? reflection = self.class.reflect_on_association(name) association = reflection.association_class.new(self, reflection) association_instance_set(name, association) end association end private # Returns the specified association instance if it responds to :loaded?, nil otherwise. def association_instance_get(name) @association_cache[name.to_sym] end # Set the specified association instance. def association_instance_set(name, association) @association_cache[name] = association end # \Associations are a set of macro-like class methods for tying objects together through # foreign keys. They express relationships like "Project has one Project Manager" # or "Project belongs to a Portfolio". Each macro adds a number of methods to the # class which are specialized according to the collection or association symbol and the # options hash. It works much the same way as Ruby's own <tt>attr*</tt> # methods. # # class Project < ActiveRecord::Base # belongs_to :portfolio # has_one :project_manager # has_many :milestones # has_and_belongs_to_many :categories # end # # The project class now has the following methods (and more) to ease the traversal and # manipulation of its relationships: # * <tt>Project#portfolio, Project#portfolio=(portfolio), Project#portfolio.nil?</tt> # * <tt>Project#project_manager, Project#project_manager=(project_manager), Project#project_manager.nil?,</tt> # * <tt>Project#milestones.empty?, Project#milestones.size, Project#milestones, Project#milestones<<(milestone),</tt> # <tt>Project#milestones.delete(milestone), Project#milestones.destroy(milestone), Project#milestones.find(milestone_id),</tt> # <tt>Project#milestones.build, Project#milestones.create</tt> # * <tt>Project#categories.empty?, Project#categories.size, Project#categories, Project#categories<<(category1),</tt> # <tt>Project#categories.delete(category1), Project#categories.destroy(category1)</tt> # # === A word of warning # # Don't create associations that have the same name as instance methods of # <tt>ActiveRecord::Base</tt>. Since the association adds a method with that name to # its model, it will override the inherited method and break things. # For instance, +attributes+ and +connection+ would be bad choices for association names. # # == Auto-generated methods # # === Singular associations (one-to-one) # | | belongs_to | # generated methods | belongs_to | :polymorphic | has_one # ----------------------------------+------------+--------------+--------- # other | X | X | X # other=(other) | X | X | X # build_other(attributes={}) | X | | X # create_other(attributes={}) | X | | X # create_other!(attributes={}) | X | | X # # ===Collection associations (one-to-many / many-to-many) # | | | has_many # generated methods | habtm | has_many | :through # ----------------------------------+-------+----------+---------- # others | X | X | X # others=(other,other,...) | X | X | X # other_ids | X | X | X # other_ids=(id,id,...) | X | X | X # others<< | X | X | X # others.push | X | X | X # others.concat | X | X | X # others.build(attributes={}) | X | X | X # others.create(attributes={}) | X | X | X # others.create!(attributes={}) | X | X | X # others.size | X | X | X # others.length | X | X | X # others.count | X | X | X # others.sum(*args) | X | X | X # others.empty? | X | X | X # others.clear | X | X | X # others.delete(other,other,...) | X | X | X # others.delete_all | X | X | X # others.destroy(other,other,...) | X | X | X # others.destroy_all | X | X | X # others.find(*args) | X | X | X # others.exists? | X | X | X # others.distinct | X | X | X # others.uniq | X | X | X # others.reset | X | X | X # # === Overriding generated methods # # Association methods are generated in a module that is included into the model class, # which allows you to easily override with your own methods and call the original # generated method with +super+. For example: # # class Car < ActiveRecord::Base # belongs_to :owner # belongs_to :old_owner # def owner=(new_owner) # self.old_owner = self.owner # super # end # end # # If your model class is <tt>Project</tt>, the module is # named <tt>Project::GeneratedFeatureMethods</tt>. The GeneratedFeatureMethods module is # included in the model class immediately after the (anonymous) generated attributes methods # module, meaning an association will override the methods for an attribute with the same name. # # == Cardinality and associations # # Active Record associations can be used to describe one-to-one, one-to-many and many-to-many # relationships between models. Each model uses an association to describe its role in # the relation. The +belongs_to+ association is always used in the model that has # the foreign key. # # === One-to-one # # Use +has_one+ in the base, and +belongs_to+ in the associated model. # # class Employee < ActiveRecord::Base # has_one :office # end # class Office < ActiveRecord::Base # belongs_to :employee # foreign key - employee_id # end # # === One-to-many # # Use +has_many+ in the base, and +belongs_to+ in the associated model. # # class Manager < ActiveRecord::Base # has_many :employees # end # class Employee < ActiveRecord::Base # belongs_to :manager # foreign key - manager_id # end # # === Many-to-many # # There are two ways to build a many-to-many relationship. # # The first way uses a +has_many+ association with the <tt>:through</tt> option and a join model, so # there are two stages of associations. # # class Assignment < ActiveRecord::Base # belongs_to :programmer # foreign key - programmer_id # belongs_to :project # foreign key - project_id # end # class Programmer < ActiveRecord::Base # has_many :assignments # has_many :projects, through: :assignments # end # class Project < ActiveRecord::Base # has_many :assignments # has_many :programmers, through: :assignments # end # # For the second way, use +has_and_belongs_to_many+ in both models. This requires a join table # that has no corresponding model or primary key. # # class Programmer < ActiveRecord::Base # has_and_belongs_to_many :projects # foreign keys in the join table # end # class Project < ActiveRecord::Base # has_and_belongs_to_many :programmers # foreign keys in the join table # end # # Choosing which way to build a many-to-many relationship is not always simple. # If you need to work with the relationship model as its own entity, # use <tt>has_many :through</tt>. Use +has_and_belongs_to_many+ when working with legacy schemas or when # you never work directly with the relationship itself. # # == Is it a +belongs_to+ or +has_one+ association? # # Both express a 1-1 relationship. The difference is mostly where to place the foreign # key, which goes on the table for the class declaring the +belongs_to+ relationship. # # class User < ActiveRecord::Base # # I reference an account. # belongs_to :account # end # # class Account < ActiveRecord::Base # # One user references me. # has_one :user # end # # The tables for these classes could look something like: # # CREATE TABLE users ( # id int(11) NOT NULL auto_increment, # account_id int(11) default NULL, # name varchar default NULL, # PRIMARY KEY (id) # ) # # CREATE TABLE accounts ( # id int(11) NOT NULL auto_increment, # name varchar default NULL, # PRIMARY KEY (id) # ) # # == Unsaved objects and associations # # You can manipulate objects and associations before they are saved to the database, but # there is some special behavior you should be aware of, mostly involving the saving of # associated objects. # # You can set the <tt>:autosave</tt> option on a <tt>has_one</tt>, <tt>belongs_to</tt>, # <tt>has_many</tt>, or <tt>has_and_belongs_to_many</tt> association. Setting it # to +true+ will _always_ save the members, whereas setting it to +false+ will # _never_ save the members. More details about <tt>:autosave</tt> option is available at # AutosaveAssociation. # # === One-to-one associations # # * Assigning an object to a +has_one+ association automatically saves that object and # the object being replaced (if there is one), in order to update their foreign # keys - except if the parent object is unsaved (<tt>new_record? == true</tt>). # * If either of these saves fail (due to one of the objects being invalid), an # <tt>ActiveRecord::RecordNotSaved</tt> exception is raised and the assignment is # cancelled. # * If you wish to assign an object to a +has_one+ association without saving it, # use the <tt>build_association</tt> method (documented below). The object being # replaced will still be saved to update its foreign key. # * Assigning an object to a +belongs_to+ association does not save the object, since # the foreign key field belongs on the parent. It does not save the parent either. # # === Collections # # * Adding an object to a collection (+has_many+ or +has_and_belongs_to_many+) automatically # saves that object, except if the parent object (the owner of the collection) is not yet # stored in the database. # * If saving any of the objects being added to a collection (via <tt>push</tt> or similar) # fails, then <tt>push</tt> returns +false+. # * If saving fails while replacing the collection (via <tt>association=</tt>), an # <tt>ActiveRecord::RecordNotSaved</tt> exception is raised and the assignment is # cancelled. # * You can add an object to a collection without automatically saving it by using the # <tt>collection.build</tt> method (documented below). # * All unsaved (<tt>new_record? == true</tt>) members of the collection are automatically # saved when the parent is saved. # # == Customizing the query # # \Associations are built from <tt>Relation</tt>s, and you can use the <tt>Relation</tt> syntax # to customize them. For example, to add a condition: # # class Blog < ActiveRecord::Base # has_many :published_posts, -> { where published: true }, class_name: 'Post' # end # # Inside the <tt>-> { ... }</tt> block you can use all of the usual <tt>Relation</tt> methods. # # === Accessing the owner object # # Sometimes it is useful to have access to the owner object when building the query. The owner # is passed as a parameter to the block. For example, the following association would find all # events that occur on the user's birthday: # # class User < ActiveRecord::Base # has_many :birthday_events, ->(user) { where starts_on: user.birthday }, class_name: 'Event' # end # # == Association callbacks # # Similar to the normal callbacks that hook into the life cycle of an Active Record object, # you can also define callbacks that get triggered when you add an object to or remove an # object from an association collection. # # class Project # has_and_belongs_to_many :developers, after_add: :evaluate_velocity # # def evaluate_velocity(developer) # ... # end # end # # It's possible to stack callbacks by passing them as an array. Example: # # class Project # has_and_belongs_to_many :developers, # after_add: [:evaluate_velocity, Proc.new { |p, d| p.shipping_date = Time.now}] # end # # Possible callbacks are: +before_add+, +after_add+, +before_remove+ and +after_remove+. # # Should any of the +before_add+ callbacks throw an exception, the object does not get # added to the collection. Same with the +before_remove+ callbacks; if an exception is # thrown the object doesn't get removed. # # == Association extensions # # The proxy objects that control the access to associations can be extended through anonymous # modules. This is especially beneficial for adding new finders, creators, and other # factory-type methods that are only used as part of this association. # # class Account < ActiveRecord::Base # has_many :people do # def find_or_create_by_name(name) # first_name, last_name = name.split(" ", 2) # find_or_create_by(first_name: first_name, last_name: last_name) # end # end # end # # person = Account.first.people.find_or_create_by_name("David Heinemeier Hansson") # person.first_name # => "David" # person.last_name # => "Heinemeier Hansson" # # If you need to share the same extensions between many associations, you can use a named # extension module. # # module FindOrCreateByNameExtension # def find_or_create_by_name(name) # first_name, last_name = name.split(" ", 2) # find_or_create_by(first_name: first_name, last_name: last_name) # end # end # # class Account < ActiveRecord::Base # has_many :people, -> { extending FindOrCreateByNameExtension } # end # # class Company < ActiveRecord::Base # has_many :people, -> { extending FindOrCreateByNameExtension } # end # # Some extensions can only be made to work with knowledge of the association's internals. # Extensions can access relevant state using the following methods (where +items+ is the # name of the association): # # * <tt>record.association(:items).owner</tt> - Returns the object the association is part of. # * <tt>record.association(:items).reflection</tt> - Returns the reflection object that describes the association. # * <tt>record.association(:items).target</tt> - Returns the associated object for +belongs_to+ and +has_one+, or # the collection of associated objects for +has_many+ and +has_and_belongs_to_many+. # # However, inside the actual extension code, you will not have access to the <tt>record</tt> as # above. In this case, you can access <tt>proxy_association</tt>. For example, # <tt>record.association(:items)</tt> and <tt>record.items.proxy_association</tt> will return # the same object, allowing you to make calls like <tt>proxy_association.owner</tt> inside # association extensions. # # == Association Join Models # # Has Many associations can be configured with the <tt>:through</tt> option to use an # explicit join model to retrieve the data. This operates similarly to a # +has_and_belongs_to_many+ association. The advantage is that you're able to add validations, # callbacks, and extra attributes on the join model. Consider the following schema: # # class Author < ActiveRecord::Base # has_many :authorships # has_many :books, through: :authorships # end # # class Authorship < ActiveRecord::Base # belongs_to :author # belongs_to :book # end # # @author = Author.first # @author.authorships.collect { |a| a.book } # selects all books that the author's authorships belong to # @author.books # selects all books by using the Authorship join model # # You can also go through a +has_many+ association on the join model: # # class Firm < ActiveRecord::Base # has_many :clients # has_many :invoices, through: :clients # end # # class Client < ActiveRecord::Base # belongs_to :firm # has_many :invoices # end # # class Invoice < ActiveRecord::Base # belongs_to :client # end # # @firm = Firm.first # @firm.clients.collect { |c| c.invoices }.flatten # select all invoices for all clients of the firm # @firm.invoices # selects all invoices by going through the Client join model # # Similarly you can go through a +has_one+ association on the join model: # # class Group < ActiveRecord::Base # has_many :users # has_many :avatars, through: :users # end # # class User < ActiveRecord::Base # belongs_to :group # has_one :avatar # end # # class Avatar < ActiveRecord::Base # belongs_to :user # end # # @group = Group.first # @group.users.collect { |u| u.avatar }.compact # select all avatars for all users in the group # @group.avatars # selects all avatars by going through the User join model. # # An important caveat with going through +has_one+ or +has_many+ associations on the # join model is that these associations are *read-only*. For example, the following # would not work following the previous example: # # @group.avatars << Avatar.new # this would work if User belonged_to Avatar rather than the other way around # @group.avatars.delete(@group.avatars.last) # so would this # # == Setting Inverses # # If you are using a +belongs_to+ on the join model, it is a good idea to set the # <tt>:inverse_of</tt> option on the +belongs_to+, which will mean that the following example # works correctly (where <tt>tags</tt> is a +has_many+ <tt>:through</tt> association): # # @post = Post.first # @tag = @post.tags.build name: "ruby" # @tag.save # # The last line ought to save the through record (a <tt>Taggable</tt>). This will only work if the # <tt>:inverse_of</tt> is set: # # class Taggable < ActiveRecord::Base # belongs_to :post # belongs_to :tag, inverse_of: :taggings # end # # If you do not set the <tt>:inverse_of</tt> record, the association will # do its best to match itself up with the correct inverse. Automatic # inverse detection only works on <tt>has_many</tt>, <tt>has_one</tt>, and # <tt>belongs_to</tt> associations. # # Extra options on the associations, as defined in the # <tt>AssociationReflection::INVALID_AUTOMATIC_INVERSE_OPTIONS</tt> constant, will # also prevent the association's inverse from being found automatically. # # The automatic guessing of the inverse association uses a heuristic based # on the name of the class, so it may not work for all associations, # especially the ones with non-standard names. # # You can turn off the automatic detection of inverse associations by setting # the <tt>:inverse_of</tt> option to <tt>false</tt> like so: # # class Taggable < ActiveRecord::Base # belongs_to :tag, inverse_of: false # end # # == Nested \Associations # # You can actually specify *any* association with the <tt>:through</tt> option, including an # association which has a <tt>:through</tt> option itself. For example: # # class Author < ActiveRecord::Base # has_many :posts # has_many :comments, through: :posts # has_many :commenters, through: :comments # end # # class Post < ActiveRecord::Base # has_many :comments # end # # class Comment < ActiveRecord::Base # belongs_to :commenter # end # # @author = Author.first # @author.commenters # => People who commented on posts written by the author # # An equivalent way of setting up this association this would be: # # class Author < ActiveRecord::Base # has_many :posts # has_many :commenters, through: :posts # end # # class Post < ActiveRecord::Base # has_many :comments # has_many :commenters, through: :comments # end # # class Comment < ActiveRecord::Base # belongs_to :commenter # end # # When using nested association, you will not be able to modify the association because there # is not enough information to know what modification to make. For example, if you tried to # add a <tt>Commenter</tt> in the example above, there would be no way to tell how to set up the # intermediate <tt>Post</tt> and <tt>Comment</tt> objects. # # == Polymorphic \Associations # # Polymorphic associations on models are not restricted on what types of models they # can be associated with. Rather, they specify an interface that a +has_many+ association # must adhere to. # # class Asset < ActiveRecord::Base # belongs_to :attachable, polymorphic: true # end # # class Post < ActiveRecord::Base # has_many :assets, as: :attachable # The :as option specifies the polymorphic interface to use. # end # # @asset.attachable = @post # # This works by using a type column in addition to a foreign key to specify the associated # record. In the Asset example, you'd need an +attachable_id+ integer column and an # +attachable_type+ string column. # # Using polymorphic associations in combination with single table inheritance (STI) is # a little tricky. In order for the associations to work as expected, ensure that you # store the base model for the STI models in the type column of the polymorphic # association. To continue with the asset example above, suppose there are guest posts # and member posts that use the posts table for STI. In this case, there must be a +type+ # column in the posts table. # # class Asset < ActiveRecord::Base # belongs_to :attachable, polymorphic: true # # def attachable_type=(sType) # super(sType.to_s.classify.constantize.base_class.to_s) # end # end # # class Post < ActiveRecord::Base # # because we store "Post" in attachable_type now dependent: :destroy will work # has_many :assets, as: :attachable, dependent: :destroy # end # # class GuestPost < Post # end # # class MemberPost < Post # end # # == Caching # # All of the methods are built on a simple caching principle that will keep the result # of the last query around unless specifically instructed not to. The cache is even # shared across methods to make it even cheaper to use the macro-added methods without # worrying too much about performance at the first go. # # project.milestones # fetches milestones from the database # project.milestones.size # uses the milestone cache # project.milestones.empty? # uses the milestone cache # project.milestones(true).size # fetches milestones from the database # project.milestones # uses the milestone cache # # == Eager loading of associations # # Eager loading is a way to find objects of a certain class and a number of named associations. # This is one of the easiest ways of to prevent the dreaded 1+N problem in which fetching 100 # posts that each need to display their author triggers 101 database queries. Through the # use of eager loading, the 101 queries can be reduced to 2. # # class Post < ActiveRecord::Base # belongs_to :author # has_many :comments # end # # Consider the following loop using the class above: # # Post.all.each do |post| # puts "Post: " + post.title # puts "Written by: " + post.author.name # puts "Last comment on: " + post.comments.first.created_on # end # # To iterate over these one hundred posts, we'll generate 201 database queries. Let's # first just optimize it for retrieving the author: # # Post.includes(:author).each do |post| # # This references the name of the +belongs_to+ association that also used the <tt>:author</tt> # symbol. After loading the posts, find will collect the +author_id+ from each one and load # all the referenced authors with one query. Doing so will cut down the number of queries # from 201 to 102. # # We can improve upon the situation further by referencing both associations in the finder with: # # Post.includes(:author, :comments).each do |post| # # This will load all comments with a single query. This reduces the total number of queries # to 3. More generally the number of queries will be 1 plus the number of associations # named (except if some of the associations are polymorphic +belongs_to+ - see below). # # To include a deep hierarchy of associations, use a hash: # # Post.includes(:author, {comments: {author: :gravatar}}).each do |post| # # That'll grab not only all the comments but all their authors and gravatar pictures. # You can mix and match symbols, arrays and hashes in any combination to describe the # associations you want to load. # # All of this power shouldn't fool you into thinking that you can pull out huge amounts # of data with no performance penalty just because you've reduced the number of queries. # The database still needs to send all the data to Active Record and it still needs to # be processed. So it's no catch-all for performance problems, but it's a great way to # cut down on the number of queries in a situation as the one described above. # # Since only one table is loaded at a time, conditions or orders cannot reference tables # other than the main one. If this is the case Active Record falls back to the previously # used LEFT OUTER JOIN based strategy. For example # # Post.includes([:author, :comments]).where(['comments.approved = ?', true]) # # This will result in a single SQL query with joins along the lines of: # <tt>LEFT OUTER JOIN comments ON comments.post_id = posts.id</tt> and # <tt>LEFT OUTER JOIN authors ON authors.id = posts.author_id</tt>. Note that using conditions # like this can have unintended consequences. # In the above example posts with no approved comments are not returned at all, because # the conditions apply to the SQL statement as a whole and not just to the association. # You must disambiguate column references for this fallback to happen, for example # <tt>order: "author.name DESC"</tt> will work but <tt>order: "name DESC"</tt> will not. # # If you do want eager load only some members of an association it is usually more natural # to include an association which has conditions defined on it: # # class Post < ActiveRecord::Base # has_many :approved_comments, -> { where approved: true }, class_name: 'Comment' # end # # Post.includes(:approved_comments) # # This will load posts and eager load the +approved_comments+ association, which contains # only those comments that have been approved. # # If you eager load an association with a specified <tt>:limit</tt> option, it will be ignored, # returning all the associated objects: # # class Picture < ActiveRecord::Base # has_many :most_recent_comments, -> { order('id DESC').limit(10) }, class_name: 'Comment' # end # # Picture.includes(:most_recent_comments).first.most_recent_comments # => returns all associated comments. # # Eager loading is supported with polymorphic associations. # # class Address < ActiveRecord::Base # belongs_to :addressable, polymorphic: true # end # # A call that tries to eager load the addressable model # # Address.includes(:addressable) # # This will execute one query to load the addresses and load the addressables with one # query per addressable type. # For example if all the addressables are either of class Person or Company then a total # of 3 queries will be executed. The list of addressable types to load is determined on # the back of the addresses loaded. This is not supported if Active Record has to fallback # to the previous implementation of eager loading and will raise <tt>ActiveRecord::EagerLoadPolymorphicError</tt>. # The reason is that the parent model's type is a column value so its corresponding table # name cannot be put in the +FROM+/+JOIN+ clauses of that query. # # == Table Aliasing # # Active Record uses table aliasing in the case that a table is referenced multiple times # in a join. If a table is referenced only once, the standard table name is used. The # second time, the table is aliased as <tt>#{reflection_name}_#{parent_table_name}</tt>. # Indexes are appended for any more successive uses of the table name. # # Post.joins(:comments) # # => SELECT ... FROM posts INNER JOIN comments ON ... # Post.joins(:special_comments) # STI # # => SELECT ... FROM posts INNER JOIN comments ON ... AND comments.type = 'SpecialComment' # Post.joins(:comments, :special_comments) # special_comments is the reflection name, posts is the parent table name # # => SELECT ... FROM posts INNER JOIN comments ON ... INNER JOIN comments special_comments_posts # # Acts as tree example: # # TreeMixin.joins(:children) # # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ... # TreeMixin.joins(children: :parent) # # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ... # INNER JOIN parents_mixins ... # TreeMixin.joins(children: {parent: :children}) # # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ... # INNER JOIN parents_mixins ... # INNER JOIN mixins childrens_mixins_2 # # Has and Belongs to Many join tables use the same idea, but add a <tt>_join</tt> suffix: # # Post.joins(:categories) # # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ... # Post.joins(categories: :posts) # # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ... # INNER JOIN categories_posts posts_categories_join INNER JOIN posts posts_categories # Post.joins(categories: {posts: :categories}) # # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ... # INNER JOIN categories_posts posts_categories_join INNER JOIN posts posts_categories # INNER JOIN categories_posts categories_posts_join INNER JOIN categories categories_posts_2 # # If you wish to specify your own custom joins using <tt>joins</tt> method, those table # names will take precedence over the eager associations: # # Post.joins(:comments).joins("inner join comments ...") # # => SELECT ... FROM posts INNER JOIN comments_posts ON ... INNER JOIN comments ... # Post.joins(:comments, :special_comments).joins("inner join comments ...") # # => SELECT ... FROM posts INNER JOIN comments comments_posts ON ... # INNER JOIN comments special_comments_posts ... # INNER JOIN comments ... # # Table aliases are automatically truncated according to the maximum length of table identifiers # according to the specific database. # # == Modules # # By default, associations will look for objects within the current module scope. Consider: # # module MyApplication # module Business # class Firm < ActiveRecord::Base # has_many :clients # end # # class Client < ActiveRecord::Base; end # end # end # # When <tt>Firm#clients</tt> is called, it will in turn call # <tt>MyApplication::Business::Client.find_all_by_firm_id(firm.id)</tt>. # If you want to associate with a class in another module scope, this can be done by # specifying the complete class name. # # module MyApplication # module Business # class Firm < ActiveRecord::Base; end # end # # module Billing # class Account < ActiveRecord::Base # belongs_to :firm, class_name: "MyApplication::Business::Firm" # end # end # end # # == Bi-directional associations # # When you specify an association there is usually an association on the associated model # that specifies the same relationship in reverse. For example, with the following models: # # class Dungeon < ActiveRecord::Base # has_many :traps # has_one :evil_wizard # end # # class Trap < ActiveRecord::Base # belongs_to :dungeon # end # # class EvilWizard < ActiveRecord::Base # belongs_to :dungeon # end # # The +traps+ association on +Dungeon+ and the +dungeon+ association on +Trap+ are # the inverse of each other and the inverse of the +dungeon+ association on +EvilWizard+ # is the +evil_wizard+ association on +Dungeon+ (and vice-versa). By default, # Active Record doesn't know anything about these inverse relationships and so no object # loading optimization is possible. For example: # # d = Dungeon.first # t = d.traps.first # d.level == t.dungeon.level # => true # d.level = 10 # d.level == t.dungeon.level # => false # # The +Dungeon+ instances +d+ and <tt>t.dungeon</tt> in the above example refer to # the same object data from the database, but are actually different in-memory copies # of that data. Specifying the <tt>:inverse_of</tt> option on associations lets you tell # Active Record about inverse relationships and it will optimise object loading. For # example, if we changed our model definitions to: # # class Dungeon < ActiveRecord::Base # has_many :traps, inverse_of: :dungeon # has_one :evil_wizard, inverse_of: :dungeon # end # # class Trap < ActiveRecord::Base # belongs_to :dungeon, inverse_of: :traps # end # # class EvilWizard < ActiveRecord::Base # belongs_to :dungeon, inverse_of: :evil_wizard # end # # Then, from our code snippet above, +d+ and <tt>t.dungeon</tt> are actually the same # in-memory instance and our final <tt>d.level == t.dungeon.level</tt> will return +true+. # # There are limitations to <tt>:inverse_of</tt> support: # # * does not work with <tt>:through</tt> associations. # * does not work with <tt>:polymorphic</tt> associations. # * for +belongs_to+ associations +has_many+ inverse associations are ignored. # # == Deleting from associations # # === Dependent associations # # +has_many+, +has_one+ and +belongs_to+ associations support the <tt>:dependent</tt> option. # This allows you to specify that associated records should be deleted when the owner is # deleted. # # For example: # # class Author # has_many :posts, dependent: :destroy # end # Author.find(1).destroy # => Will destroy all of the author's posts, too # # The <tt>:dependent</tt> option can have different values which specify how the deletion # is done. For more information, see the documentation for this option on the different # specific association types. When no option is given, the behavior is to do nothing # with the associated records when destroying a record. # # Note that <tt>:dependent</tt> is implemented using Rails' callback # system, which works by processing callbacks in order. Therefore, other # callbacks declared either before or after the <tt>:dependent</tt> option # can affect what it does. # # === Delete or destroy? # # +has_many+ and +has_and_belongs_to_many+ associations have the methods <tt>destroy</tt>, # <tt>delete</tt>, <tt>destroy_all</tt> and <tt>delete_all</tt>. # # For +has_and_belongs_to_many+, <tt>delete</tt> and <tt>destroy</tt> are the same: they # cause the records in the join table to be removed. # # For +has_many+, <tt>destroy</tt> and <tt>destroy_all</tt> will always call the <tt>destroy</tt> method of the # record(s) being removed so that callbacks are run. However <tt>delete</tt> and <tt>delete_all</tt> will either # do the deletion according to the strategy specified by the <tt>:dependent</tt> option, or # if no <tt>:dependent</tt> option is given, then it will follow the default strategy. # The default strategy is <tt>:nullify</tt> (set the foreign keys to <tt>nil</tt>), except for # +has_many+ <tt>:through</tt>, where the default strategy is <tt>delete_all</tt> (delete # the join records, without running their callbacks). # # There is also a <tt>clear</tt> method which is the same as <tt>delete_all</tt>, except that # it returns the association rather than the records which have been deleted. # # === What gets deleted? # # There is a potential pitfall here: +has_and_belongs_to_many+ and +has_many+ <tt>:through</tt> # associations have records in join tables, as well as the associated records. So when we # call one of these deletion methods, what exactly should be deleted? # # The answer is that it is assumed that deletion on an association is about removing the # <i>link</i> between the owner and the associated object(s), rather than necessarily the # associated objects themselves. So with +has_and_belongs_to_many+ and +has_many+ # <tt>:through</tt>, the join records will be deleted, but the associated records won't. # # This makes sense if you think about it: if you were to call <tt>post.tags.delete(Tag.find_by(name: 'food'))</tt> # you would want the 'food' tag to be unlinked from the post, rather than for the tag itself # to be removed from the database. # # However, there are examples where this strategy doesn't make sense. For example, suppose # a person has many projects, and each project has many tasks. If we deleted one of a person's # tasks, we would probably not want the project to be deleted. In this scenario, the delete method # won't actually work: it can only be used if the association on the join model is a # +belongs_to+. In other situations you are expected to perform operations directly on # either the associated records or the <tt>:through</tt> association. # # With a regular +has_many+ there is no distinction between the "associated records" # and the "link", so there is only one choice for what gets deleted. # # With +has_and_belongs_to_many+ and +has_many+ <tt>:through</tt>, if you want to delete the # associated records themselves, you can always do something along the lines of # <tt>person.tasks.each(&:destroy)</tt>. # # == Type safety with <tt>ActiveRecord::AssociationTypeMismatch</tt> # # If you attempt to assign an object to an association that doesn't match the inferred # or specified <tt>:class_name</tt>, you'll get an <tt>ActiveRecord::AssociationTypeMismatch</tt>. # # == Options # # All of the association macros can be specialized through options. This makes cases # more complex than the simple and guessable ones possible. module ClassMethods # Specifies a one-to-many association. The following methods for retrieval and query of # collections of associated objects will be added: # # [collection(force_reload = false)] # Returns an array of all the associated objects. # An empty array is returned if none are found. # [collection<<(object, ...)] # Adds one or more objects to the collection by setting their foreign keys to the collection's primary key. # Note that this operation instantly fires update SQL without waiting for the save or update call on the # parent object, unless the parent object is a new record. # [collection.delete(object, ...)] # Removes one or more objects from the collection by setting their foreign keys to +NULL+. # Objects will be in addition destroyed if they're associated with <tt>dependent: :destroy</tt>, # and deleted if they're associated with <tt>dependent: :delete_all</tt>. # # If the <tt>:through</tt> option is used, then the join records are deleted (rather than # nullified) by default, but you can specify <tt>dependent: :destroy</tt> or # <tt>dependent: :nullify</tt> to override this. # [collection.destroy(object, ...)] # Removes one or more objects from the collection by running <tt>destroy</tt> on # each record, regardless of any dependent option, ensuring callbacks are run. # # If the <tt>:through</tt> option is used, then the join records are destroyed # instead, not the objects themselves. # [collection=objects] # Replaces the collections content by deleting and adding objects as appropriate. If the <tt>:through</tt> # option is true callbacks in the join models are triggered except destroy callbacks, since deletion is # direct. # [collection_singular_ids] # Returns an array of the associated objects' ids # [collection_singular_ids=ids] # Replace the collection with the objects identified by the primary keys in +ids+. This # method loads the models and calls <tt>collection=</tt>. See above. # [collection.clear] # Removes every object from the collection. This destroys the associated objects if they # are associated with <tt>dependent: :destroy</tt>, deletes them directly from the # database if <tt>dependent: :delete_all</tt>, otherwise sets their foreign keys to +NULL+. # If the <tt>:through</tt> option is true no destroy callbacks are invoked on the join models. # Join models are directly deleted. # [collection.empty?] # Returns +true+ if there are no associated objects. # [collection.size] # Returns the number of associated objects. # [collection.find(...)] # Finds an associated object according to the same rules as <tt>ActiveRecord::Base.find</tt>. # [collection.exists?(...)] # Checks whether an associated object with the given conditions exists. # Uses the same rules as <tt>ActiveRecord::Base.exists?</tt>. # [collection.build(attributes = {}, ...)] # Returns one or more new objects of the collection type that have been instantiated # with +attributes+ and linked to this object through a foreign key, but have not yet # been saved. # [collection.create(attributes = {})] # Returns a new object of the collection type that has been instantiated # with +attributes+, linked to this object through a foreign key, and that has already # been saved (if it passed the validation). *Note*: This only works if the base model # already exists in the DB, not if it is a new (unsaved) record! # [collection.create!(attributes = {})] # Does the same as <tt>collection.create</tt>, but raises <tt>ActiveRecord::RecordInvalid</tt> # if the record is invalid. # # (*Note*: +collection+ is replaced with the symbol passed as the first argument, so # <tt>has_many :clients</tt> would add among others <tt>clients.empty?</tt>.) # # === Example # # A <tt>Firm</tt> class declares <tt>has_many :clients</tt>, which will add: # * <tt>Firm#clients</tt> (similar to <tt>Client.where(firm_id: id)</tt>) # * <tt>Firm#clients<<</tt> # * <tt>Firm#clients.delete</tt> # * <tt>Firm#clients.destroy</tt> # * <tt>Firm#clients=</tt> # * <tt>Firm#client_ids</tt> # * <tt>Firm#client_ids=</tt> # * <tt>Firm#clients.clear</tt> # * <tt>Firm#clients.empty?</tt> (similar to <tt>firm.clients.size == 0</tt>) # * <tt>Firm#clients.size</tt> (similar to <tt>Client.count "firm_id = #{id}"</tt>) # * <tt>Firm#clients.find</tt> (similar to <tt>Client.where(firm_id: id).find(id)</tt>) # * <tt>Firm#clients.exists?(name: 'ACME')</tt> (similar to <tt>Client.exists?(name: 'ACME', firm_id: firm.id)</tt>) # * <tt>Firm#clients.build</tt> (similar to <tt>Client.new("firm_id" => id)</tt>) # * <tt>Firm#clients.create</tt> (similar to <tt>c = Client.new("firm_id" => id); c.save; c</tt>) # * <tt>Firm#clients.create!</tt> (similar to <tt>c = Client.new("firm_id" => id); c.save!</tt>) # The declaration can also include an options hash to specialize the behavior of the association. # # === Options # [:class_name] # Specify the class name of the association. Use it only if that name can't be inferred # from the association name. So <tt>has_many :products</tt> will by default be linked # to the Product class, but if the real class name is SpecialProduct, you'll have to # specify it with this option. # [:foreign_key] # Specify the foreign key used for the association. By default this is guessed to be the name # of this class in lower-case and "_id" suffixed. So a Person class that makes a +has_many+ # association will use "person_id" as the default <tt>:foreign_key</tt>. # [:primary_key] # Specify the method that returns the primary key used for the association. By default this is +id+. # [:dependent] # Controls what happens to the associated objects when # their owner is destroyed. Note that these are implemented as # callbacks, and Rails executes callbacks in order. Therefore, other # similar callbacks may affect the <tt>:dependent</tt> behavior, and the # <tt>:dependent</tt> behavior may affect other callbacks. # # * <tt>:destroy</tt> causes all the associated objects to also be destroyed. # * <tt>:delete_all</tt> causes all the associated objects to be deleted directly from the database (so callbacks will not be executed). # * <tt>:nullify</tt> causes the foreign keys to be set to +NULL+. Callbacks are not executed. # * <tt>:restrict_with_exception</tt> causes an exception to be raised if there are any associated records. # * <tt>:restrict_with_error</tt> causes an error to be added to the owner if there are any associated objects. # # If using with the <tt>:through</tt> option, the association on the join model must be # a +belongs_to+, and the records which get deleted are the join records, rather than # the associated records. # [:counter_cache] # This option can be used to configure a custom named <tt>:counter_cache.</tt> You only need this option, # when you customized the name of your <tt>:counter_cache</tt> on the <tt>belongs_to</tt> association. # [:as] # Specifies a polymorphic interface (See <tt>belongs_to</tt>). # [:through] # Specifies an association through which to perform the query. This can be any other type # of association, including other <tt>:through</tt> associations. Options for <tt>:class_name</tt>, # <tt>:primary_key</tt> and <tt>:foreign_key</tt> are ignored, as the association uses the # source reflection. # # If the association on the join model is a +belongs_to+, the collection can be modified # and the records on the <tt>:through</tt> model will be automatically created and removed # as appropriate. Otherwise, the collection is read-only, so you should manipulate the # <tt>:through</tt> association directly. # # If you are going to modify the association (rather than just read from it), then it is # a good idea to set the <tt>:inverse_of</tt> option on the source association on the # join model. This allows associated records to be built which will automatically create # the appropriate join model records when they are saved. (See the 'Association Join Models' # section above.) # [:source] # Specifies the source association name used by <tt>has_many :through</tt> queries. # Only use it if the name cannot be inferred from the association. # <tt>has_many :subscribers, through: :subscriptions</tt> will look for either <tt>:subscribers</tt> or # <tt>:subscriber</tt> on Subscription, unless a <tt>:source</tt> is given. # [:source_type] # Specifies type of the source association used by <tt>has_many :through</tt> queries where the source # association is a polymorphic +belongs_to+. # [:validate] # If +false+, don't validate the associated objects when saving the parent object. true by default. # [:autosave] # If true, always save the associated objects or destroy them if marked for destruction, # when saving the parent object. If false, never save or destroy the associated objects. # By default, only save associated objects that are new records. This option is implemented as a # +before_save+ callback. Because callbacks are run in the order they are defined, associated objects # may need to be explicitly saved in any user-defined +before_save+ callbacks. # # Note that <tt>accepts_nested_attributes_for</tt> sets <tt>:autosave</tt> to <tt>true</tt>. # [:inverse_of] # Specifies the name of the <tt>belongs_to</tt> association on the associated object # that is the inverse of this <tt>has_many</tt> association. Does not work in combination # with <tt>:through</tt> or <tt>:as</tt> options. # See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail. # # Option examples: # has_many :comments, -> { order "posted_on" } # has_many :comments, -> { includes :author } # has_many :people, -> { where("deleted = 0").order("name") }, class_name: "Person" # has_many :tracks, -> { order "position" }, dependent: :destroy # has_many :comments, dependent: :nullify # has_many :tags, as: :taggable # has_many :reports, -> { readonly } # has_many :subscribers, through: :subscriptions, source: :user def has_many(name, scope = nil, options = {}, &extension) Builder::HasMany.build(self, name, scope, options, &extension) end # Specifies a one-to-one association with another class. This method should only be used # if the other class contains the foreign key. If the current class contains the foreign key, # then you should use +belongs_to+ instead. See also ActiveRecord::Associations::ClassMethods's overview # on when to use +has_one+ and when to use +belongs_to+. # # The following methods for retrieval and query of a single associated object will be added: # # [association(force_reload = false)] # Returns the associated object. +nil+ is returned if none is found. # [association=(associate)] # Assigns the associate object, extracts the primary key, sets it as the foreign key, # and saves the associate object. # [build_association(attributes = {})] # Returns a new object of the associated type that has been instantiated # with +attributes+ and linked to this object through a foreign key, but has not # yet been saved. # [create_association(attributes = {})] # Returns a new object of the associated type that has been instantiated # with +attributes+, linked to this object through a foreign key, and that # has already been saved (if it passed the validation). # [create_association!(attributes = {})] # Does the same as <tt>create_association</tt>, but raises <tt>ActiveRecord::RecordInvalid</tt> # if the record is invalid. # # (+association+ is replaced with the symbol passed as the first argument, so # <tt>has_one :manager</tt> would add among others <tt>manager.nil?</tt>.) # # === Example # # An Account class declares <tt>has_one :beneficiary</tt>, which will add: # * <tt>Account#beneficiary</tt> (similar to <tt>Beneficiary.where(account_id: id).first</tt>) # * <tt>Account#beneficiary=(beneficiary)</tt> (similar to <tt>beneficiary.account_id = account.id; beneficiary.save</tt>) # * <tt>Account#build_beneficiary</tt> (similar to <tt>Beneficiary.new("account_id" => id)</tt>) # * <tt>Account#create_beneficiary</tt> (similar to <tt>b = Beneficiary.new("account_id" => id); b.save; b</tt>) # * <tt>Account#create_beneficiary!</tt> (similar to <tt>b = Beneficiary.new("account_id" => id); b.save!; b</tt>) # # === Options # # The declaration can also include an options hash to specialize the behavior of the association. # # Options are: # [:class_name] # Specify the class name of the association. Use it only if that name can't be inferred # from the association name. So <tt>has_one :manager</tt> will by default be linked to the Manager class, but # if the real class name is Person, you'll have to specify it with this option. # [:dependent] # Controls what happens to the associated object when # its owner is destroyed: # # * <tt>:destroy</tt> causes the associated object to also be destroyed # * <tt>:delete</tt> causes the associated object to be deleted directly from the database (so callbacks will not execute) # * <tt>:nullify</tt> causes the foreign key to be set to +NULL+. Callbacks are not executed. # * <tt>:restrict_with_exception</tt> causes an exception to be raised if there is an associated record # * <tt>:restrict_with_error</tt> causes an error to be added to the owner if there is an associated object # [:foreign_key] # Specify the foreign key used for the association. By default this is guessed to be the name # of this class in lower-case and "_id" suffixed. So a Person class that makes a +has_one+ association # will use "person_id" as the default <tt>:foreign_key</tt>. # [:primary_key] # Specify the method that returns the primary key used for the association. By default this is +id+. # [:as] # Specifies a polymorphic interface (See <tt>belongs_to</tt>). # [:through] # Specifies a Join Model through which to perform the query. Options for <tt>:class_name</tt>, # <tt>:primary_key</tt>, and <tt>:foreign_key</tt> are ignored, as the association uses the # source reflection. You can only use a <tt>:through</tt> query through a <tt>has_one</tt> # or <tt>belongs_to</tt> association on the join model. # [:source] # Specifies the source association name used by <tt>has_one :through</tt> queries. # Only use it if the name cannot be inferred from the association. # <tt>has_one :favorite, through: :favorites</tt> will look for a # <tt>:favorite</tt> on Favorite, unless a <tt>:source</tt> is given. # [:source_type] # Specifies type of the source association used by <tt>has_one :through</tt> queries where the source # association is a polymorphic +belongs_to+. # [:validate] # If +false+, don't validate the associated object when saving the parent object. +false+ by default. # [:autosave] # If true, always save the associated object or destroy it if marked for destruction, # when saving the parent object. If false, never save or destroy the associated object. # By default, only save the associated object if it's a new record. # # Note that <tt>accepts_nested_attributes_for</tt> sets <tt>:autosave</tt> to <tt>true</tt>. # [:inverse_of] # Specifies the name of the <tt>belongs_to</tt> association on the associated object # that is the inverse of this <tt>has_one</tt> association. Does not work in combination # with <tt>:through</tt> or <tt>:as</tt> options. # See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail. # # Option examples: # has_one :credit_card, dependent: :destroy # destroys the associated credit card # has_one :credit_card, dependent: :nullify # updates the associated records foreign # # key value to NULL rather than destroying it # has_one :last_comment, -> { order 'posted_on' }, class_name: "Comment" # has_one :project_manager, -> { where role: 'project_manager' }, class_name: "Person" # has_one :attachment, as: :attachable # has_one :boss, readonly: :true # has_one :club, through: :membership # has_one :primary_address, -> { where primary: true }, through: :addressables, source: :addressable def has_one(name, scope = nil, options = {}) Builder::HasOne.build(self, name, scope, options) end # Specifies a one-to-one association with another class. This method should only be used # if this class contains the foreign key. If the other class contains the foreign key, # then you should use +has_one+ instead. See also ActiveRecord::Associations::ClassMethods's overview # on when to use +has_one+ and when to use +belongs_to+. # # Methods will be added for retrieval and query for a single associated object, for which # this object holds an id: # # [association(force_reload = false)] # Returns the associated object. +nil+ is returned if none is found. # [association=(associate)] # Assigns the associate object, extracts the primary key, and sets it as the foreign key. # [build_association(attributes = {})] # Returns a new object of the associated type that has been instantiated # with +attributes+ and linked to this object through a foreign key, but has not yet been saved. # [create_association(attributes = {})] # Returns a new object of the associated type that has been instantiated # with +attributes+, linked to this object through a foreign key, and that # has already been saved (if it passed the validation). # [create_association!(attributes = {})] # Does the same as <tt>create_association</tt>, but raises <tt>ActiveRecord::RecordInvalid</tt> # if the record is invalid. # # (+association+ is replaced with the symbol passed as the first argument, so # <tt>belongs_to :author</tt> would add among others <tt>author.nil?</tt>.) # # === Example # # A Post class declares <tt>belongs_to :author</tt>, which will add: # * <tt>Post#author</tt> (similar to <tt>Author.find(author_id)</tt>) # * <tt>Post#author=(author)</tt> (similar to <tt>post.author_id = author.id</tt>) # * <tt>Post#build_author</tt> (similar to <tt>post.author = Author.new</tt>) # * <tt>Post#create_author</tt> (similar to <tt>post.author = Author.new; post.author.save; post.author</tt>) # * <tt>Post#create_author!</tt> (similar to <tt>post.author = Author.new; post.author.save!; post.author</tt>) # The declaration can also include an options hash to specialize the behavior of the association. # # === Options # # [:class_name] # Specify the class name of the association. Use it only if that name can't be inferred # from the association name. So <tt>belongs_to :author</tt> will by default be linked to the Author class, but # if the real class name is Person, you'll have to specify it with this option. # [:foreign_key] # Specify the foreign key used for the association. By default this is guessed to be the name # of the association with an "_id" suffix. So a class that defines a <tt>belongs_to :person</tt> # association will use "person_id" as the default <tt>:foreign_key</tt>. Similarly, # <tt>belongs_to :favorite_person, class_name: "Person"</tt> will use a foreign key # of "favorite_person_id". # [:foreign_type] # Specify the column used to store the associated object's type, if this is a polymorphic # association. By default this is guessed to be the name of the association with a "_type" # suffix. So a class that defines a <tt>belongs_to :taggable, polymorphic: true</tt> # association will use "taggable_type" as the default <tt>:foreign_type</tt>. # [:primary_key] # Specify the method that returns the primary key of associated object used for the association. # By default this is id. # [:dependent] # If set to <tt>:destroy</tt>, the associated object is destroyed when this object is. If set to # <tt>:delete</tt>, the associated object is deleted *without* calling its destroy method. # This option should not be specified when <tt>belongs_to</tt> is used in conjunction with # a <tt>has_many</tt> relationship on another class because of the potential to leave # orphaned records behind. # [:counter_cache] # Caches the number of belonging objects on the associate class through the use of +increment_counter+ # and +decrement_counter+. The counter cache is incremented when an object of this # class is created and decremented when it's destroyed. This requires that a column # named <tt>#{table_name}_count</tt> (such as +comments_count+ for a belonging Comment class) # is used on the associate class (such as a Post class) - that is the migration for # <tt>#{table_name}_count</tt> is created on the associate class (such that <tt>Post.comments_count</tt> will # return the count cached, see note below). You can also specify a custom counter # cache column by providing a column name instead of a +true+/+false+ value to this # option (e.g., <tt>counter_cache: :my_custom_counter</tt>.) # Note: Specifying a counter cache will add it to that model's list of readonly attributes # using +attr_readonly+. # [:polymorphic] # Specify this association is a polymorphic association by passing +true+. # Note: If you've enabled the counter cache, then you may want to add the counter cache attribute # to the +attr_readonly+ list in the associated classes (e.g. <tt>class Post; attr_readonly :comments_count; end</tt>). # [:validate] # If +false+, don't validate the associated objects when saving the parent object. +false+ by default. # [:autosave] # If true, always save the associated object or destroy it if marked for destruction, when # saving the parent object. # If false, never save or destroy the associated object. # By default, only save the associated object if it's a new record. # # Note that <tt>accepts_nested_attributes_for</tt> sets <tt>:autosave</tt> to <tt>true</tt>. # [:touch] # If true, the associated object will be touched (the updated_at/on attributes set to now) # when this record is either saved or destroyed. If you specify a symbol, that attribute # will be updated with the current time in addition to the updated_at/on attribute. # [:inverse_of] # Specifies the name of the <tt>has_one</tt> or <tt>has_many</tt> association on the associated # object that is the inverse of this <tt>belongs_to</tt> association. Does not work in # combination with the <tt>:polymorphic</tt> options. # See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail. # # Option examples: # belongs_to :firm, foreign_key: "client_of" # belongs_to :person, primary_key: "name", foreign_key: "person_name" # belongs_to :author, class_name: "Person", foreign_key: "author_id" # belongs_to :valid_coupon, ->(o) { where "discounts > #{o.payments_count}" }, # class_name: "Coupon", foreign_key: "coupon_id" # belongs_to :attachable, polymorphic: true # belongs_to :project, readonly: true # belongs_to :post, counter_cache: true # belongs_to :company, touch: true # belongs_to :company, touch: :employees_last_updated_at def belongs_to(name, scope = nil, options = {}) Builder::BelongsTo.build(self, name, scope, options) end # Specifies a many-to-many relationship with another class. This associates two classes via an # intermediate join table. Unless the join table is explicitly specified as an option, it is # guessed using the lexical order of the class names. So a join between Developer and Project # will give the default join table name of "developers_projects" because "D" precedes "P" alphabetically. # Note that this precedence is calculated using the <tt><</tt> operator for String. This # means that if the strings are of different lengths, and the strings are equal when compared # up to the shortest length, then the longer string is considered of higher # lexical precedence than the shorter one. For example, one would expect the tables "paper_boxes" and "papers" # to generate a join table name of "papers_paper_boxes" because of the length of the name "paper_boxes", # but it in fact generates a join table name of "paper_boxes_papers". Be aware of this caveat, and use the # custom <tt>:join_table</tt> option if you need to. # If your tables share a common prefix, it will only appear once at the beginning. For example, # the tables "catalog_categories" and "catalog_products" generate a join table name of "catalog_categories_products". # # The join table should not have a primary key or a model associated with it. You must manually generate the # join table with a migration such as this: # # class CreateDevelopersProjectsJoinTable < ActiveRecord::Migration # def change # create_table :developers_projects, id: false do |t| # t.integer :developer_id # t.integer :project_id # end # end # end # # It's also a good idea to add indexes to each of those columns to speed up the joins process. # However, in MySQL it is advised to add a compound index for both of the columns as MySQL only # uses one index per table during the lookup. # # Adds the following methods for retrieval and query: # # [collection(force_reload = false)] # Returns an array of all the associated objects. # An empty array is returned if none are found. # [collection<<(object, ...)] # Adds one or more objects to the collection by creating associations in the join table # (<tt>collection.push</tt> and <tt>collection.concat</tt> are aliases to this method). # Note that this operation instantly fires update SQL without waiting for the save or update call on the # parent object, unless the parent object is a new record. # [collection.delete(object, ...)] # Removes one or more objects from the collection by removing their associations from the join table. # This does not destroy the objects. # [collection.destroy(object, ...)] # Removes one or more objects from the collection by running destroy on each association in the join table, overriding any dependent option. # This does not destroy the objects. # [collection=objects] # Replaces the collection's content by deleting and adding objects as appropriate. # [collection_singular_ids] # Returns an array of the associated objects' ids. # [collection_singular_ids=ids] # Replace the collection by the objects identified by the primary keys in +ids+. # [collection.clear] # Removes every object from the collection. This does not destroy the objects. # [collection.empty?] # Returns +true+ if there are no associated objects. # [collection.size] # Returns the number of associated objects. # [collection.find(id)] # Finds an associated object responding to the +id+ and that # meets the condition that it has to be associated with this object. # Uses the same rules as <tt>ActiveRecord::Base.find</tt>. # [collection.exists?(...)] # Checks whether an associated object with the given conditions exists. # Uses the same rules as <tt>ActiveRecord::Base.exists?</tt>. # [collection.build(attributes = {})] # Returns a new object of the collection type that has been instantiated # with +attributes+ and linked to this object through the join table, but has not yet been saved. # [collection.create(attributes = {})] # Returns a new object of the collection type that has been instantiated # with +attributes+, linked to this object through the join table, and that has already been # saved (if it passed the validation). # # (+collection+ is replaced with the symbol passed as the first argument, so # <tt>has_and_belongs_to_many :categories</tt> would add among others <tt>categories.empty?</tt>.) # # === Example # # A Developer class declares <tt>has_and_belongs_to_many :projects</tt>, which will add: # * <tt>Developer#projects</tt> # * <tt>Developer#projects<<</tt> # * <tt>Developer#projects.delete</tt> # * <tt>Developer#projects.destroy</tt> # * <tt>Developer#projects=</tt> # * <tt>Developer#project_ids</tt> # * <tt>Developer#project_ids=</tt> # * <tt>Developer#projects.clear</tt> # * <tt>Developer#projects.empty?</tt> # * <tt>Developer#projects.size</tt> # * <tt>Developer#projects.find(id)</tt> # * <tt>Developer#projects.exists?(...)</tt> # * <tt>Developer#projects.build</tt> (similar to <tt>Project.new("developer_id" => id)</tt>) # * <tt>Developer#projects.create</tt> (similar to <tt>c = Project.new("developer_id" => id); c.save; c</tt>) # The declaration may include an options hash to specialize the behavior of the association. # # === Options # # [:class_name] # Specify the class name of the association. Use it only if that name can't be inferred # from the association name. So <tt>has_and_belongs_to_many :projects</tt> will by default be linked to the # Project class, but if the real class name is SuperProject, you'll have to specify it with this option. # [:join_table] # Specify the name of the join table if the default based on lexical order isn't what you want. # <b>WARNING:</b> If you're overwriting the table name of either class, the +table_name+ method # MUST be declared underneath any +has_and_belongs_to_many+ declaration in order to work. # [:foreign_key] # Specify the foreign key used for the association. By default this is guessed to be the name # of this class in lower-case and "_id" suffixed. So a Person class that makes # a +has_and_belongs_to_many+ association to Project will use "person_id" as the # default <tt>:foreign_key</tt>. # [:association_foreign_key] # Specify the foreign key used for the association on the receiving side of the association. # By default this is guessed to be the name of the associated class in lower-case and "_id" suffixed. # So if a Person class makes a +has_and_belongs_to_many+ association to Project, # the association will use "project_id" as the default <tt>:association_foreign_key</tt>. # [:readonly] # If true, all the associated objects are readonly through the association. # [:validate] # If +false+, don't validate the associated objects when saving the parent object. +true+ by default. # [:autosave] # If true, always save the associated objects or destroy them if marked for destruction, when # saving the parent object. # If false, never save or destroy the associated objects. # By default, only save associated objects that are new records. # # Note that <tt>accepts_nested_attributes_for</tt> sets <tt>:autosave</tt> to <tt>true</tt>. # # Option examples: # has_and_belongs_to_many :projects # has_and_belongs_to_many :projects, -> { includes :milestones, :manager } # has_and_belongs_to_many :nations, class_name: "Country" # has_and_belongs_to_many :categories, join_table: "prods_cats" # has_and_belongs_to_many :categories, -> { readonly } def has_and_belongs_to_many(name, scope = nil, options = {}, &extension) Builder::HasAndBelongsToMany.build(self, name, scope, options, &extension) end end end end