module Sequel::Plugins::NestedAttributes

  1. lib/sequel/plugins/nested_attributes.rb

The nested_attributes plugin allows you to create, update, and delete associated objects directly by calling a method on the current object. Nested attributes are defined using the nested_attributes class method:

Artist.one_to_many :albums
Artist.plugin :nested_attributes
Artist.nested_attributes :albums

The nested_attributes call defines a single method, association_attributes=, (e.g. albums_attributes=). So if you have an Artist instance:

a = 'YJM')

You can create new album instances related to this artist:

a.albums_attributes = [{name: 'RF'}, {name: 'MO'}]

Note that this doesn’t send any queries to the database yet. That doesn’t happen till you save the object:

That will save the artist first, and then save both albums. If either the artist is invalid or one of the albums is invalid, none of the objects will be saved to the database, and all related validation errors will be available in the artist’s validation errors.

In addition to creating new associated objects, you can also update existing associated objects. You just need to make sure that the primary key field is filled in for the associated object:

a.update(albums_attributes: [{id: 1, name: 'T'}])

Since the primary key field is filled in, the plugin will update the album with id 1 instead of creating a new album.

If you would like to delete the associated object instead of updating it, you add a _delete entry to the hash, and also pass the :destroy option when calling nested_attributes:

Artist.nested_attributes :albums, destroy: true
a.update(albums_attributes: [{id: 1, _delete: true}])

This will delete the related associated object from the database. If you want to leave the associated object in the database, but just remove it from the association, add a _remove entry in the hash, and also pass the :remove option when calling nested_attributes:

Artist.nested_attributes :albums, remove: true
a.update(albums_attributes: [{id: 1, _remove: true}])

The above example was for a one_to_many association, but the plugin also works similarly for other association types. For one_to_one and many_to_one associations, you need to pass a single hash instead of an array of hashes.

This plugin is mainly designed to make it easy to use on html forms, where a single form submission can contained nested attributes (and even nested attributes of those attributes). You just need to name your form inputs correctly:


Your web stack will probably parse that into a nested hash similar to:

{'artist'=>{'name'=>'Y', 'albums_attributes'=>{'0'=>{'name'=>'X'}, '1'=>{'id'=>'2', 'name'=>'Z'}}}}

Then you can do:

artist.update_fields(params['artist'], %w'name albums_attributes')

Note that Rails 5+ does not use a Hash for submitted parameters, and therefore the above will not work. With Rails 5+, you have to use:

artist.update_fields(params.to_unsafe_h['artist'], %w'name albums_attributes')

To save changes to the artist, create the first album and associate it to the artist, and update the other existing associated album.

You can pass options for individual nested attributes, which will override the default nested attributes options for that association. This is useful for per-call filtering of the allowed fields:

a.set_nested_attributes(:albums, params['artist'], fields: %w'name')


Public Class

  1. apply

Public Class methods


Depend on the validate_associated plugin.

[show source]
   # File lib/sequel/plugins/nested_attributes.rb
90 def self.apply(model)
91   model.plugin(:validate_associated)
92 end