Accepts_nested_attributes_for with belongs_to polymorphic

Question

I would like to establish a polymorphic relation with accepts_nested_attributes_for . Here is the code:

 class Contact <ActiveRecord::Base has_many :jobs, :as=>:client end class Job <ActiveRecord::Base belongs_to :client, :polymorphic=>:true accepts_nested_attributes_for :client end 

When I try to access Job.create(..., :client_attributes=>{...} , they give me NameError: uninitialized constant Job::Client

Answer 1

I just realized that rails do not support this behavior, so I came up with the following workaround:

 class Job <ActiveRecord::Base belongs_to :client, :polymorphic=>:true, :autosave=>true accepts_nested_attributes_for :client def attributes=(attributes = {}) self.client_type = attributes[:client_type] super end def client_attributes=(attributes) self.client = type.constantize.find_or_initialize_by_id(attributes.delete(:client_id)) if client_type.valid? end end 

This gives me the opportunity to customize my form as follows:

 <%= f.select :client_type %> <%= f.fields_for :client do |client|%> <%= client.text_field :name %> <% end %> 

Not an exact solution, but an idea is important.

Answer 2

I also had a problem with "ArgumentError: Unable to create association model name. Are you trying to build a one-to-one polymorphic association?"

And I found the best solution for this kind of problem. You can use your own method. Let's look at the implementation of nested_attributes, inside Rails3:

 elsif !reject_new_record?(association_name, attributes) method = "build_#{association_name}" if respond_to?(method) send(method, attributes.except(*UNASSIGNABLE_KEYS)) else raise ArgumentError, "Cannot build association #{association_name}. Are you trying to build a polymorphic one-to-one association?" end end 

So what do we need to do here? It is easy to create build _ # {association_name} inside our model. I made a full working example below:

 class Job <ActiveRecord::Base CLIENT_TYPES = %w(Contact) attr_accessible :client_type, :client_attributes belongs_to :client, :polymorphic => :true accepts_nested_attributes_for :client protected def build_client(params, assignment_options) raise "Unknown client_type: #{client_type}" unless CLIENT_TYPES.include?(client_type) self.client = client_type.constantize.new(params) end end 

Answer 3

I finally got this to work with Rails 4.x. This is based on Dmitry / Scott's answer, therefore +1 to them.

STEP 1. To get started, here is a complete model with polymorphic association:

 # app/models/polymorph.rb class Polymorph < ActiveRecord::Base belongs_to :associable, polymorphic: true accepts_nested_attributes_for :associable def build_associable(params) self.associable = associable_type.constantize.new(params) end end # For the sake of example: # app/models/chicken.rb class Chicken < ActiveRecord::Base has_many: :polymorphs, as: :associable end 

Yes, this is nothing new. However, you may wonder where polymorph_type comes from and how is its value set? This is part of the database entry because polymorphic associations add the columns <association_name>_id and <association_name>_type . However, when build_associable is executed, the value of _type is nil .

STEP 2. Skip and accept the type of child

Submit the form in the child_type form along with typical form data, and your controller should enable it when checking strong parameters.

 # app/views/polymorph/_form.html.erb <%= form_for(@polymorph) do |form| %> # Pass in the child_type - This one has been turned into a chicken! <%= form.hidden_field(:polymorph_type, value: 'Chicken' %> ... # Form values for Chicken <%= form.fields_for(:chicken) do |chicken_form| %> <%= chicken_form.text_field(:hunger_level) %> <%= chicken_form.text_field(:poop_level) %> ...etc... <% end %> <% end %> # app/controllers/polymorph_controllers.erb ... private def polymorph_params params.require(:polymorph).permit(:id, :polymorph_id, :polymorph_type) end 

Of course, your views will have to handle the various types of models that are “related”, but this demonstrates one.

Hope this helps someone. (Why do you need polymorphic chickens?)

Answer 4

The above answer is great, but does not work with the setting shown. This inspired me, and I was able to create a working solution:

works to create and update

 class Job <ActiveRecord::Base belongs_to :client, :polymorphic=>:true attr_accessible :client_attributes accepts_nested_attributes_for :client def attributes=(attributes = {}) self.client_type = attributes[:client_type] super end def client_attributes=(attributes) some_client = self.client_type.constantize.find_or_initilize_by_id(self.client_id) some_client.attributes = attributes self.client = some_client end end