Module: ActiveRecord::NestedAttributes::ClassMethods
- Defined in:
- lib/active_record/nested_attributes.rb
Overview
Nested Attributes
Nested attributes allow you to save attributes on associated records through the parent. By default nested attribute updating is turned off, 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.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_attributes 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 _delete
key to the attributes hash, with a value that evaluates to true
, you will destroy the associated model:
member.avatar_attributes = { :id => '2', :_delete => '1' }
member.avatar.marked_for_destruction? # => true
member.save
member.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 an associated post model through the attribute hash.
For each hash that does not have an id
key a new record will be instantiated, unless the hash also contains a _delete
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 => '', :_delete => '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'
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 _delete
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', :_delete => '1' }]
}}
member.attributes = params['member']
member.posts.detect { |p| p.id == 2 }.marked_for_destruction? # => true
member.posts.length #=> 2
member.save
member.posts.length # => 1
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.
Instance Method Summary collapse
-
#accepts_nested_attributes_for(*attr_names) ⇒ Object
Defines an attributes writer for the specified association(s).
Instance Method Details
#accepts_nested_attributes_for(*attr_names) ⇒ Object
Defines an attributes writer for the specified association(s). If you are using attr_protected
or attr_accessible
, then you will need to add the attribute writer to the allowed list.
Supported options:
- :allow_destroy
-
If true, destroys any members from the attributes hash with a
_delete
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 that checks whether a record should be built for a certain attribute hash. The hash is passed to the Proc and the Proc should return either
true
orfalse
. When no Proc is specified a record will be built for all attribute hashes that do not have a_delete
that evaluates to true.
Examples:
# creates avatar_attributes=
accepts_nested_attributes_for :avatar, :reject_if => proc { |attributes| attributes['name'].blank? }
# creates avatar_attributes= and posts_attributes=
accepts_nested_attributes_for :avatar, :posts, :allow_destroy => true
189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 |
# File 'lib/active_record/nested_attributes.rb', line 189 def accepts_nested_attributes_for(*attr_names) = { :allow_destroy => false } .update(attr_names.) .assert_valid_keys(:allow_destroy, :reject_if) attr_names.each do |association_name| if reflection = reflect_on_association(association_name) type = case reflection.macro when :has_one, :belongs_to :one_to_one when :has_many, :has_and_belongs_to_many :collection end reflection.[:autosave] = true self.reject_new_nested_attributes_procs[association_name.to_sym] = [:reject_if] # def pirate_attributes=(attributes) # assign_nested_attributes_for_one_to_one_association(:pirate, attributes, false) # end class_eval %{ def #{association_name}_attributes=(attributes) assign_nested_attributes_for_#{type}_association(:#{association_name}, attributes, #{[:allow_destroy]}) end }, __FILE__, __LINE__ else raise ArgumentError, "No association found for name `#{association_name}'. Has it been defined yet?" end end end |