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Nested Attributes
Nested attributes provide a mechanism for updating documents and their relations in a single operation, by nesting attributes in a single parameters hash. This is extremely useful when wanting to edit multiple documents within a single web form.
Common Behaviour
Nested attributes can be enabled for any relation, embedded or
referenced. To enable this for the relation, simply provide the relation
name to the accepts_nested_attributes_for
macro.
class Band include Mongoid::Document embeds_many :albums belongs_to :producer accepts_nested_attributes_for :albums, :producer end
Note that when you add nested attributes functionality to a
referenced relation, Mongoid will automatically enable
|
When a relation gains nested attributes behavior, an additional method
is added to the base model, which should be used to update the attributes
with the new functionality. This method is the relation name plus
_attributes=
. You can use this method directly, or more commonly
the name of the method can be an attribute in the updates for the base class,
in which case Mongoid will call the appropriate setter under the covers.
band = Band.first band.producer_attributes = { name: "Flood" } band.attributes = { producer_attributes: { name: "Flood" }}
Note that this will work with any attribute based setter method in
Mongoid. This includes: update_attributes
,
update_attributes!
and attributes=
. For full
examples of every single scenario you could possibly imagine, see the
One Spec to Rule them All.
Operations
The following table shows the means of setting nested attributes for the different types of relations, as well as the required and optional options.
1-1 Operations
1-1 operations include embeds_one
,
embedded_in
, has_one
, and belongs_to
.
Operation | Syntax | Definition |
---|---|---|
Set the relation via nested attributes, or replace the existing one. |
album.producer_attributes = { name: "Flood" } album.attributes = { producer_attributes: { name: "Flood" }} |
class Album include Mongoid::Document belongs_to :producer accepts_nested_attributes_for :producer end |
Update the existing relation - an id or _id must be provided in this case of the existing document. |
album.producer_attributes = { id: ..., name: "Flood" } album.attributes = { producer_attributes: { id: ..., name: "Flood" } } |
class Album include Mongoid::Document belongs_to :producer accepts_nested_attributes_for :producer end |
Reject nested attributes if they don't match a certain criteria. |
album.producer_attributes = { name: "Flood" } album.attributes = { producer_attributes: { name: "Flood" } } |
class Album include Mongoid::Document belongs_to :producer accepts_nested_attributes_for :producer, reject_if: ->(attrs){ attrs[:name] == "Flood" } end |
Reject nested attributes if all the fields are blank. |
album.producer_attributes = { name: "", label: "" } album.attributes = { producer_attributes = { name: "", label: "" } } |
class Album include Mongoid::Document belongs_to :producer accepts_nested_attributes_for :producer, reject_if: :all_blank end |
Delete an existing 1-1 relation via nested attributes. The attributes must all match, and a _destroy truthy value must be passed. |
album.producer_attributes = { name: "Flood", _destroy: "1" } album.attributes = { producer_attributes: { name: "Flood", _destroy: "1" } } |
class Album include Mongoid::Document belongs_to :producer accepts_nested_attributes_for :producer, allow_destroy: true end |
Update an existing relation, never create a new one - even if the id or _id does not match. |
album.producer_attributes = { id: ..., name: "Flood" } album.attributes = { producer_attributes: { id: ..., name: "Flood" } } |
class Album include Mongoid::Document belongs_to :producer accepts_nested_attributes_for :producer, update_only: true end |
1-n/n-n Operations
1-n/n-n operations include embeds_many
,
has_many
and has_and_belongs_to_many
. These
attribute hashes can take either a hash of hashes, with arbitrary keys
for each document, or an array with a hash for each document in it.
Operation | Syntax | Definition |
---|---|---|
Create a new document on the relation |
band.albums_attributes = { "0" => { name: "Violator" } } band.albums_attributes = [ { name: "Violator" } ] band.attributes = { albums_attributes: { "0" => { name: "Violator" } } } |
class Band include Mongoid::Document embeds_many :albums accepts_nested_attributes_for :albums end |
Limit the number of new documents that can be created in a single set, raising an error if more are passed in. |
band.albums_attributes = { "0" => { name: "Violator" }, "1" => { name: "101" }, "2" => { name: "Music for the Masses" } } band.attributes = { albums_attributes: { "0" => { name: "Violator" }, "1" => { name: "101" }, "2" => { name: "Music for the Masses" } } } |
class Band include Mongoid::Document embeds_many :albums accepts_nested_attributes_for :albums, limit: 2 end |
Update existing documents in the relation - id or _id must be provided in the attributes for each document. |
band.albums_attributes = { "0" => { id: ..., name: "Violator (Edit)" }, "1" => { id: ..., name: "101 (Edit)" } } band.albums_attributes = [ { id: ..., name: "Violator (Edit)" }, { id: ..., name: "101 (Edit)" } ] band.attributes = { albums_attributes: { "0" => { id: ..., name: "Violator (Edit)" }, "1" => { id: ..., name: "101 (Edit)" } } } |
class Band include Mongoid::Document embeds_many :albums accepts_nested_attributes_for :albums end |
Delete a document in the relation - id or _id must be passed in along with the _destroy truthy value. |
band.albums_attributes = { "0" => { id: ..., _destroy: "1" }, } band.albums_attributes = [ { id: ..., _destroy: "1" }, ] band.attributes = { albums_attributes: { "0" => { id: ..., _destroy: "1" }, } } |
class Band include Mongoid::Document embeds_many :albums accepts_nested_attributes_for :albums, allow_destroy: true end |
Reject nested attributes if they don't match a certain criteria. |
band.albums_attributes = { "0" => { name: "Violator" } } band.albums_attributes = [ { name: "Violator" } ] band.attributes = { albums_attributes: { "0" => { name: "Violator" } } } |
class Band include Mongoid::Document embeds_many :albums accepts_nested_attributes_for :albums, reject_if: ->(attrs){ attrs[:name] == "Violator" } end |
Reject nested attributes if all the fields are blank. |
band.albums_attributes = { "0" => { name: "" } } band.albums_attributes = [ { name: "" } ] band.attributes = { albums_attributes: { "0" => { name: "" } } } |
class Band include Mongoid::Document embeds_many :albums accepts_nested_attributes_for :albums, reject_if: :all_blank end |