Rails 4 nested form with has_many, through and multiple select - ruby-on-rails

Question

I have a problem with nested form and has_many relation. Bussiness case: there are laboratories and their suppliers. Suppliers can be shared between labs.
Models
class Lab < ActiveRecord::Base
has_many :lab_suppliers
has_many :suppliers, through: :lab_suppliers
accepts_nested_attributes_for :lab_suppliers
end
class Supplier < ActiveRecord::Base
has_many :lab_suppliers
has_many :labs, through: :lab_suppliers
accepts_nested_attributes_for :lab_suppliers
end
class LabSupplier < ActiveRecord::Base
belongs_to :lab
belongs_to :supplier
accepts_nested_attributes_for :lab
accepts_nested_attributes_for :supplier
end
Form
<%= form_for(#lab) do |f| %>
<div class="field">
<%= f.label :code %><br>
<%= f.text_field :code %>
</div>
<div class="field">
<%= f.label :name %><br>
<%= f.text_field :name %>
</div>
<div class"field">
<%= fields_for :lab_suppliers do |ff| %>
<%= ff.label :supplier_id %><br>
<%= ff.collection_select :supplier_id, Supplier.all, :id, :name, {include_blank: true}, {:multiple => true, :class=>""} %>
<% end %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
Controller
class LabsController < ApplicationController
before_action :set_lab, only: [:show, :edit, :update, :destroy]
# GET /labs/new
def new
#lab = Lab.new
#lab.lab_suppliers.build
end
# POST /labs
# POST /labs.json
def create
#raise params.inspect
#lab = Lab.new(lab_params)
#lab_supplier = #lab.lab_suppliers.new(params[:lab_suppliers])
#lab_supplier.save
#lab.save
private
def lab_params
params.require(:lab).permit(:code, :name, lab_suppliers_attributes: [])
end
end
Result of the inspect on params after submitting form:
Parameters:
{"utf8"=>"✓",
"authenticity_token"=>"...",
"lab"=>{"code"=>"L01",
"name"=>"xxx"},
"lab_suppliers"=>{"supplier_id"=>["",
"1",
"3"]},
"commit"=>"Create Lab"}
While submitting form I receive ActiveModel::ForbiddenAttributesError
on the line:
#lab_supplier = #lab.lab_suppliers.new(params[:lab_suppliers])
What am i missing to make it work as expected?

Answer 1

It seems like you need to explicitly tell lab_params which attributes from lab_suppliers you need to pass like:
params.require(:lab).permit(:code, :name, lab_suppliers_attributes: [:supplier_id])
Try it and let me know.

Answer 2

Link to other post that helped me to find the working solution:
[Rails nested form with multiple entries
Below I provide the working solution showing how to pass values from the multiple select as nested attributes and insert them to the db.
Models
class Lab < ActiveRecord::Base
has_many :lab_suppliers#, :foreign_key => 'lab_id', dependent: :destroy
has_many :suppliers, through: :lab_suppliers
accepts_nested_attributes_for :lab_suppliers, :allow_destroy => true
end
class Supplier < ActiveRecord::Base
has_many :lab_suppliers
has_many :labs, through: :lab_suppliers
end
class LabSupplier < ActiveRecord::Base
belongs_to :lab
belongs_to :supplier
end
Comment:
accepts_nested_attributes_for is put only on has_many/has_one side. No need to put it on belongs_to side
Form (Lab)
<%= form_for(#lab) do |f| %>
<div class="field">
<%= f.label :code %><br>
<%= f.text_field :code %>
</div>
<div class="field">
<%= f.label :name %><br>
<%= f.text_field :name %>
</div>
<div class"field">
<%= f.fields_for :lab_suppliers do |ff| %>
<%= ff.label :supplier_id %><br>
<%= ff.collection_select :supplier_id, Supplier.all, :id, :name, {include_blank: true}, {:multiple => true, :class=>""} %>
<% end %>
<%= f.submit %><% end %>
Controller
Comment:
There is no need to permit any additional params in supplier or lab_suppliers controllers
class LabsController < ApplicationController
before_action :set_lab, only: [:show, :edit, :update, :destroy]
def new
#lab = Lab.new
#lab.lab_suppliers.build
end
def create
#lab = Lab.new(lab_params)
#startcount=1 #start counting from 1 because the first element in the array of nested params is always null
#lab.lab_suppliers.each do |m|
#raise lab_params[:lab_suppliers_attributes]["0"][:supplier_id][#startcount].inspect
m.supplier_id = lab_params[:lab_suppliers_attributes]["0"][:supplier_id][#startcount]
#startcount +=1
end
respond_to do |format|
if #lab.save
lab_params[:lab_suppliers_attributes]["0"][:supplier_id].drop(#startcount).each do |m|
#lab.lab_suppliers.build(:supplier_id => lab_params[:lab_suppliers_attributes]["0"][:supplier_id][#startcount]).save
#startcount += 1
end
format.html { redirect_to labs_path, notice: 'Lab was successfully created.' }
format.json { render :show, status: :created, location: #lab }
else
format.html { render :new }
format.json { render json: #lab.errors, status: :unprocessable_entity }
end
end
end
private
def lab_params
params.require(:lab).permit(:name, :code, lab_suppliers_attributes: [supplier_id: [] ])
end
end
Comment: supplier_id: [] in the lab_suppliers_attributes permitts array of values from the multiple dropdown to be passed