accepts_nested_attributes_for(*attr_names) public

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:


If true, destroys any members from the attributes hash with a _destroy key and a value that evaluates to true (eg. 1, ‘1’, true, or ‘true’). This option is off by default.


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 or false. 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.


Allows you to specify the maximum number of the associated records that can be processed with the nested attributes. 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.


Allows you to specify that an existing record may only be updated. A new record may only be created when there is no existing record. This option only works for one-to-one associations and is ignored for collection associations. This option is off by default.


# 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
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April 28, 2009
6 thanks

A very thorough explanation of use

Ryan Daigle has a great article about 2.3’s new nest forms which does a really good job of explaining how to use this and some of the potential gotchas. Highly recommended:

June 30, 2009
3 thanks

Be careful with name of attribute writer

If restricting access to attributes you normally get code like

attr_accessible :foo,  

When using these nested attributes you end up with code like

attr_accessible :foo, :bar_attributes

Its very easy to leave of the _attributes suffix e.g

attr_accessible :foo, :bar

which will cause you all sorts of problems

March 8, 2011 - (>= v2.3.8)
3 thanks

Dont use _delete

Most blog articles about accepts_nested_attributes_for, including the one from @mattsa and @annaswims, tell you to add a

'_delete' => 1

when you want a deletion checkbox, hidden attribute, etc.

But this stopped being true a while ago. This is just a “Watch Out!” Make sure you use

'_destroy' => 1


November 12, 2010
1 thank

nested attribute gotcha

Just adding to what @diabolist said :

class House

has_many :doors
accepts_nested_attributes_for :doors

attr_accesible :address, :doors_attributes
# NOTE its plural


June 5, 2014
0 thanks

Reject If

reject_if: proc { |attributes| attributes[‘name’].blank? } Has saved me after an 3 hours of google search. Thanks

November 12, 2009
0 thanks

Rails documentation for nested attributes


(don’t follow this link, the url interpreter isn’t rendering it correctly :(, but the correct link is at the top of this page)

November 18, 2009
0 thanks

More Docs and Explanation

You probably want to look at the class level docs

(cut and paste, apidocks can’t render the above for some reason)

March 20, 2009
0 thanks

Nested Model Forms

For a good example of nested model forms check out the rails blog.