Active Record Associations

This is the root class of all associations (‘+ Foo’ signifies an included module Foo):

Association
  SingularAssociation
    HasOneAssociation + ForeignAssociation
      HasOneThroughAssociation + ThroughAssociation
    BelongsToAssociation
      BelongsToPolymorphicAssociation
  CollectionAssociation
    HasManyAssociation + ForeignAssociation
      HasManyThroughAssociation + ThroughAssociation

Associations in Active Record are middlemen between the object that holds the association, known as the owner, and the associated result set, known as the target. Association metadata is available in reflection, which is an instance of ActiveRecord::Reflection::AssociationReflection.

For example, given

class Blog < ActiveRecord::Base
  has_many :posts
end

blog = Blog.first

The association of blog.posts has the object blog as its owner, the collection of its posts as target, and the reflection object represents a :has_many macro.

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