Rails Associations - Callback Sequence/Magic
- by satynos
Taking following association declaration as an example:
class Post
has_many :comments
end
Just by declaring the has_many :comments, ActiveRecord adds several methods of which I am particularly interested in comments which returns array of comments. I browsed through the code and following seems to be the callback sequence:
def has_many(association_id, options = {}, &extension)
reflection = create_has_many_reflection(association_id, options, &extension)
configure_dependency_for_has_many(reflection)
add_association_callbacks(reflection.name, reflection.options)
if options[:through]
collection_accessor_methods(reflection, HasManyThroughAssociation)
else
collection_accessor_methods(reflection, HasManyAssociation)
end
end
def collection_accessor_methods(reflection, association_proxy_class, writer = true)
collection_reader_method(reflection, association_proxy_class)
if writer
define_method("#{reflection.name}=") do |new_value|
# Loads proxy class instance (defined in collection_reader_method) if not already loaded
association = send(reflection.name)
association.replace(new_value)
association
end
define_method("#{reflection.name.to_s.singularize}_ids=") do |new_value|
ids = (new_value || []).reject { |nid| nid.blank? }
send("#{reflection.name}=", reflection.class_name.constantize.find(ids))
end
end
end
def collection_reader_method(reflection, association_proxy_class)
define_method(reflection.name) do |*params|
force_reload = params.first unless params.empty?
association = association_instance_get(reflection.name)
unless association
association = association_proxy_class.new(self, reflection)
association_instance_set(reflection.name, association)
end
association.reload if force_reload
association
end
define_method("#{reflection.name.to_s.singularize}_ids") do
if send(reflection.name).loaded? || reflection.options[:finder_sql]
send(reflection.name).map(&:id)
else
send(reflection.name).all(:select => "#{reflection.quoted_table_name}.#{reflection.klass.primary_key}").map(&:id)
end
end
end
In this sequence of callbacks, where exactly is the actual SQL being executed for retrieving the comments when I do @post.comments ?
