module ActiveRecord::NestedAttributes::ClassMethods
Active Record Nested Attributes
Nested attributes allow you to save attributes on associated records through the parent. By default nested attribute updating is turned off and you can enable it using the #accepts_nested_attributes_for class method. When you enable nested attributes an attribute writer is defined on the model.
The attribute writer is named after the association, which means that in the following example, two new methods are added to your model:
author_attributes=(attributes)
and pages_attributes=(attributes)
.
class Book < ActiveRecord::Base
has_one :author
has_many :pages
accepts_nested_attributes_for :author, :pages
end
Note that the :autosave
option is automatically enabled on every association that #accepts_nested_attributes_for is used for.
One-to-one
Consider a Member model that has one Avatar:
class Member < ActiveRecord::Base
has_one :avatar
accepts_nested_attributes_for :avatar
end
Enabling nested attributes on a one-to-one association allows you to create the member and avatar in one go:
params = { member: { name: 'Jack', avatar_attributes: { icon: 'smiling' } } }
member = Member.create(params[:member])
member.avatar.id # => 2
member.avatar.icon # => 'smiling'
It also allows you to update the avatar through the member:
params = { member: { avatar_attributes: { id: '2', icon: 'sad' } } }
member.update params[:member]
member.avatar.icon # => 'sad'
By default you will only be able to set and update attributes on the associated model. If you want to destroy the associated model through the attributes hash, you have to enable it first using the :allow_destroy
option.
class Member < ActiveRecord::Base
has_one :avatar
accepts_nested_attributes_for :avatar, allow_destroy: true
end
Now, when you add the _destroy
key to the attributes hash, with a value that evaluates to true
, you will destroy the associated model:
member.avatar_attributes = { id: '2', _destroy: '1' }
member.avatar.marked_for_destruction? # => true
member.save
member.reload.avatar # => nil
Note that the model will not be destroyed until the parent is saved.
One-to-many
Consider a member that has a number of posts:
class Member < ActiveRecord::Base
has_many :posts
accepts_nested_attributes_for :posts
end
You can now set or update attributes on the associated posts through an attribute hash for a member: include the key :posts_attributes
with an array of hashes of post attributes as a value.
For each hash that does not have an id
key a new record will be instantiated, unless the hash also contains a _destroy
key that evaluates to true
.
params = { member: {
name: 'joe', posts_attributes: [
{ title: 'Kari, the awesome Ruby documentation browser!' },
{ title: 'The egalitarian assumption of the modern citizen' },
{ title: '', _destroy: '1' } # this will be ignored
]
}}
member = Member.create(params[:member])
member.posts.length # => 2
member.posts.first.title # => 'Kari, the awesome Ruby documentation browser!'
member.posts.second.title # => 'The egalitarian assumption of the modern citizen'
You may also set a :reject_if proc to silently ignore any new record hashes if they fail to pass your criteria. For example, the previous example could be rewritten as:
class Member < ActiveRecord::Base
has_many :posts
accepts_nested_attributes_for :posts, reject_if: proc { |attributes| attributes['title'].blank? }
end
params = { member: {
name: 'joe', posts_attributes: [
{ title: 'Kari, the awesome Ruby documentation browser!' },
{ title: 'The egalitarian assumption of the modern citizen' },
{ title: '' } # this will be ignored because of the :reject_if proc
]
}}
member = Member.create(params[:member])
member.posts.length # => 2
member.posts.first.title # => 'Kari, the awesome Ruby documentation browser!'
member.posts.second.title # => 'The egalitarian assumption of the modern citizen'
Alternatively, :reject_if also accepts a symbol for using methods:
class Member < ActiveRecord::Base
has_many :posts
accepts_nested_attributes_for :posts, reject_if: :new_record?
end
class Member < ActiveRecord::Base
has_many :posts
accepts_nested_attributes_for :posts, reject_if: :reject_posts
def reject_posts(attributed)
attributed['title'].blank?
end
end
If the hash contains an id
key that matches an already associated record, the matching record will be modified:
member.attributes = {
name: 'Joe',
posts_attributes: [
{ id: 1, title: '[UPDATED] An, as of yet, undisclosed awesome Ruby documentation browser!' },
{ id: 2, title: '[UPDATED] other post' }
]
}
member.posts.first.title # => '[UPDATED] An, as of yet, undisclosed awesome Ruby documentation browser!'
member.posts.second.title # => '[UPDATED] other post'
By default the associated records are protected from being destroyed. If you want to destroy any of the associated records through the attributes hash, you have to enable it first using the :allow_destroy
option. This will allow you to also use the _destroy
key to destroy existing records:
class Member < ActiveRecord::Base
has_many :posts
accepts_nested_attributes_for :posts, allow_destroy: true
end
params = { member: {
posts_attributes: [{ id: '2', _destroy: '1' }]
}}
member.attributes = params[:member]
member.posts.detect { |p| p.id == 2 }.marked_for_destruction? # => true
member.posts.length # => 2
member.save
member.reload.posts.length # => 1
Nested attributes for an associated collection can also be passed in the form of a hash of hashes instead of an array of hashes:
Member.create(name: 'joe',
posts_attributes: { first: { title: 'Foo' },
second: { title: 'Bar' } })
has the same effect as
Member.create(name: 'joe',
posts_attributes: [ { title: 'Foo' },
{ title: 'Bar' } ])
The keys of the hash which is the value for :posts_attributes
are ignored in this case. However, it is not allowed to use +'id'+ or :id
for one of such keys, otherwise the hash will be wrapped in an array and interpreted as an attribute hash for a single post.
Passing attributes for an associated collection in the form of a hash of hashes can be used with hashes generated from HTTP/HTML parameters, where there maybe no natural way to submit an array of hashes.
Saving
All changes to models, including the destruction of those marked for destruction, are saved and destroyed automatically and atomically when the parent model is saved. This happens inside the transaction initiated by the parents save method. See ActiveRecord::AutosaveAssociation.
Validating the presence of a parent model
If you want to validate that a child record is associated with a parent record, you can use validates_presence_of
and inverse_of
as this example illustrates:
class Member < ActiveRecord::Base
has_many :posts, inverse_of: :member
accepts_nested_attributes_for :posts
end
class Post < ActiveRecord::Base
belongs_to :member, inverse_of: :posts
validates_presence_of :member
end
Note that if you do not specify the inverse_of
option, then Active Record will try to automatically guess the inverse association based on heuristics.
For one-to-one nested associations, if you build the new (in-memory) child object yourself before assignment, then this module will not overwrite it, e.g.:
class Member < ActiveRecord::Base
has_one :avatar
accepts_nested_attributes_for :avatar
def avatar
super || build_avatar(width: 200)
end
end
member = Member.new
member.avatar_attributes = {icon: 'sad'}
member.avatar.width # => 200
Constants
- REJECT_ALL_BLANK_PROC
Public Instance Methods
# File activerecord/lib/active_record/nested_attributes.rb, line 301
def accepts_nested_attributes_for(*attr_names)
options = { :allow_destroy => false, :update_only => false }
options.update(attr_names.extract_options!)
options.assert_valid_keys(:allow_destroy, :reject_if, :limit, :update_only)
options[:reject_if] = REJECT_ALL_BLANK_PROC if options[:reject_if] == :all_blank
attr_names.each do |association_name|
if reflection = _reflect_on_association(association_name)
reflection.autosave = true
define_autosave_validation_callbacks(reflection)
nested_attributes_options = self.nested_attributes_options.dup
nested_attributes_options[association_name.to_sym] = options
self.nested_attributes_options = nested_attributes_options
type = (reflection.collection? ? :collection : :one_to_one)
generate_association_writer(association_name, type)
else
raise ArgumentError, "No association found for name `#{association_name}'. Has it been defined yet?"
end
end
end
Defines an attributes writer for the specified association(s).
Supported options:
- :allow_destroy
-
If true, destroys any members from the attributes hash with a
_destroy
key and a value that evaluates totrue
(eg. 1, '1', true, or 'true'). This option is off by default. - :reject_if
-
Allows you to specify a Proc or a Symbol pointing to a method that checks whether a record should be built for a certain attribute hash. The hash is passed to the supplied Proc or the method and it should return either
true
orfalse
. When no :reject_if is specified, a record will be built for all attribute hashes that do not have a_destroy
value that evaluates to true. Passing:all_blank
instead of a Proc will create a proc that will reject a record where all the attributes are blank excluding any value for _destroy. - :limit
-
Allows you to specify the maximum number of the associated records that can be processed with the nested attributes. Limit also can be specified as a Proc or a Symbol pointing to a method that should return number. If the size of the nested attributes array exceeds the specified limit, NestedAttributes::TooManyRecords exception is raised. If omitted, any number associations can be processed. Note that the :limit option is only applicable to one-to-many associations.
- :update_only
-
For a one-to-one association, this option allows you to specify how nested attributes are to be used when an associated record already exists. In general, an existing record may either be updated with the new set of attribute values or be replaced by a wholly new record containing those values. By default the :update_only option is
false
and the nested attributes are used to update the existing record only if they include the record's:id
value. Otherwise a new record will be instantiated and used to replace the existing one. However if the :update_only option istrue
, the nested attributes are used to update the record's attributes always, regardless of whether the:id
is present. The option is ignored for collection associations.
Examples:
# creates avatar_attributes=
accepts_nested_attributes_for :avatar, reject_if: proc { |attributes| attributes['name'].blank? }
# creates avatar_attributes=
accepts_nested_attributes_for :avatar, reject_if: :all_blank
# creates avatar_attributes= and posts_attributes=
accepts_nested_attributes_for :avatar, :posts, allow_destroy: true
© 2004–2018 David Heinemeier Hansson
Licensed under the MIT License.