ruby-on-rails join nested-attributes has-many-through cocoon-gem

Simple form with has_many through and join table

I have models: Product, Parts and ProductParts

product.rb

class Product < ApplicationRecord
  has_many :product_parts
  has_many :parts, through: :product_parts
  accepts_nested_attributes_for :product_parts, allow_destroy: true
end

part.rb

class Part < ApplicationRecord
  has_many :product_parts
  has_many :products, through: :product_parts
end

product_part.rb

class ProductPart < ApplicationRecord
  belongs_to :part
  belongs_to :product
end

The product may consist of several parts for e.g product1 = 1pcs part2 and 3pcs part 3.

I have join table: product_parts

  create_table "product_parts", force: :cascade do |t|
    t.integer "part_id"
    t.integer "product_id"
    t.integer "quantity"
    t.index ["part_id"], name: "index_product_parts_on_part_id"
    t.index ["product_id"], name: "index_product_parts_on_product_id"
  end

I would like to render simple form for new Product, where:

I can input product name
select parts (from all parts) and define each part quantity

I have _form.html.slim like this:

= simple_form_for(@product) do |f|
  = f.error_notification
  = f.error_notification message: f.object.errors[:base].to_sentence if f.object.errors[:base].present?
  = f.input :name
  = f.simple_fields_for :parts do |part|
    = f.label :part.name
    = f.input :part.quantity
  = f.button :submit

but it doesn't render anything. Do You have any tips how to do it in correct way?

I've also tried to do it like this:

_form.html.slim

= simple_form_for(@product) do |f|
  = f.input :name
  = f.simple_fields_for :parts do |part|
    == render 'part_fields'
  = f.button :submit

_part_fields.html.slim

= :name
= part.input :quantity

Server log output is:

17:34:21 web.1       | Started GET "/products/new" for ::1 at 2020-08-24 17:34:21 +0200
17:34:21 web.1       | Processing by ProductsController#new as HTML
17:34:21 web.1       |   Rendering products/new.html.slim within layouts/application
17:34:21 web.1       |   Part Load (0.1ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   CACHE Part Load (0.0ms)  SELECT "parts".* FROM "parts" LIMIT ?  [["LIMIT", 11]]
17:34:21 web.1       |   ↳ app/views/products/_form.html.slim:6
17:34:21 web.1       |   Rendered products/_part_fields.html.slim (Duration: 442.5ms | Allocations: 233999)
17:34:21 web.1       |   Rendered products/_form.html.slim (Duration: 449.1ms | Allocations: 240331)
17:34:21 web.1       |   Rendered products/new.html.slim within layouts/application (Duration: 451.5ms | Allocations: 242361)
17:34:21 web.1       | Completed 500 Internal Server Error in 454ms (ActiveRecord: 0.4ms | Allocations: 243658)
17:34:21 web.1       |
17:34:21 web.1       |
17:34:21 web.1       |
17:34:21 web.1       | ActionView::Template::Error - undefined local variable or method `part' for #<#<Class:0x00007f938cd03f28>:0x00007f938cd020b0>
17:34:21 web.1       | Did you mean?  @parts:
17:34:21 web.1       |   app/views/products/_part_fields.html.slim:2:in `view template'

Thank You all for your answers. I found sample on GitHub: rails-recipes. Now I am using cocoon gem and I am almost there where I want to be:) but:

_form.html.slim

= simple_form_for(@product) do |f|
  = f.input :name
  |Parts
  fieldset#parts
    = f.simple_fields_for :product_parts do |product_part|
      == render 'product_part_fields', f: product_part
      = link_to_add_association 'Add part', f, :product_parts, class: 'btn btn-primary btn-xs'
    = f.button :submit

_product_part.html.slim:

.nested_fields.field
  = f.input :quantity
  = f.collection_select :part_id, Part.all, :id, :name
  = link_to_remove_association f

When form is rendered I have already two parts inputs instead of one (this should be correct). I don't want to create new part just select parts from list and insert only quantity. It looks like this: screenshot of rendered form

Product is not creating, after reload form I have always fields for 2 parts more. Here is console log:

12:58:14 web.1       | Started POST "/products" for ::1 at 2020-08-28 12:58:14 +0200
12:58:14 web.1       | Processing by ProductsController#create as HTML
12:58:14 web.1       |   Parameters: {"authenticity_token"=>"dLVq3gUUeHnmFgVxQ7gXATOF3wdQ75a/csjmjzYN6HFrr9duoi50M4KzrSUNj/QHCrJgXO2myJPdpkybdTB0cA==", "product"=>{"name"=>"Product #1", "product_parts_attributes"=>{"0"=>{"quantity"=>"4", "part_id"=>"134", "_destroy"=>"false"}, "1"=>{"quantity"=>"5", "part_id"=>"168", "_destroy"=>"false"}, "2"=>{"quantity"=>"", "part_id"=>"266", "_destroy"=>"false"}, "3"=>{"quantity"=>"", "part_id"=>"260", "_destroy"=>"false"}, "4"=>{"quantity"=>"", "part_id"=>"262", "_destroy"=>"false"}, "5"=>{"quantity"=>"", "part_id"=>"259", "_destroy"=>"false"}}}, "commit"=>"Create Product"}
12:58:14 web.1       |    (0.2ms)  begin transaction
12:58:14 web.1       |   ↳ app/controllers/products_controller.rb:29:in `block in create'
12:58:14 web.1       |   Part Load (0.2ms)  SELECT "parts".* FROM "parts" WHERE "parts"."id" = ? LIMIT ?  [["id", 134], ["LIMIT", 1]]
12:58:14 web.1       |   ↳ app/controllers/products_controller.rb:29:in `block in create'
12:58:14 web.1       |   Part Load (0.1ms)  SELECT "parts".* FROM "parts" WHERE "parts"."id" = ? LIMIT ?  [["id", 168], ["LIMIT", 1]]
12:58:14 web.1       |   ↳ app/controllers/products_controller.rb:29:in `block in create'
12:58:14 web.1       |   Part Load (0.1ms)  SELECT "parts".* FROM "parts" WHERE "parts"."id" = ? LIMIT ?  [["id", 266], ["LIMIT", 1]]
12:58:14 web.1       |   ↳ app/controllers/products_controller.rb:29:in `block in create'
12:58:14 web.1       |   Part Load (0.1ms)  SELECT "parts".* FROM "parts" WHERE "parts"."id" = ? LIMIT ?  [["id", 260], ["LIMIT", 1]]
12:58:14 web.1       |   ↳ app/controllers/products_controller.rb:29:in `block in create'
12:58:14 web.1       |   Part Load (0.1ms)  SELECT "parts".* FROM "parts" WHERE "parts"."id" = ? LIMIT ?  [["id", 262], ["LIMIT", 1]]
12:58:14 web.1       |   ↳ app/controllers/products_controller.rb:29:in `block in create'
12:58:14 web.1       |   Part Load (0.1ms)  SELECT "parts".* FROM "parts" WHERE "parts"."id" = ? LIMIT ?  [["id", 259], ["LIMIT", 1]]
12:58:14 web.1       |   ↳ app/controllers/products_controller.rb:29:in `block in create'
12:58:14 web.1       |    (0.2ms)  rollback transaction
12:58:14 web.1       |   ↳ app/controllers/products_controller.rb:29:in `block in create'

What I am doing wrong with this?:

I have two parts to choose instead of one in new rendered form
Products and products_parts cannot be created

Solution

I figured it out!:) I put working code below if somebody will have the same problem.

product.rb

class Product < ApplicationRecord
  has_many :product_parts
  has_many :parts, through: :product_parts
  accepts_nested_attributes_for :parts, reject_if: blank?, allow_destroy: false
  accepts_nested_attributes_for :product_parts, allow_destroy: true
end

product_part.rb

class ProductPart < ApplicationRecord
  belongs_to :part
  belongs_to :product

  accepts_nested_attributes_for :part, reject_if: all_blank
end

part.rb

class Part < ApplicationRecord
  has_many :product_parts
  has_many :products, through: :product_parts
end

products_controller.rb

# GET /products/new
def new
  @product = Product.new
  @product.product_parts.build.build_part
end

products/_form.html.slim

= simple_form_for(@product) do |f|
  = f.error_notification
  = f.error_notification message: f.object.errors[:base].to_sentence if f.object.errors[:base].present?
  = f.input :name, label: false, class: 'form-control', placeholder: t('placeholders.input_product_name')
  fieldset#parts
    = f.simple_fields_for :product_parts do |product_part|
      .field
        == render 'product_part_fields', f: product_part
    = link_to_add_association 'Add part', f, :product_parts, class: 'btn btn-primary btn-xs'
    = f.button :submit

products/_product_part_fields.html.slim

.nested-fields.field
  .field.has-addons
    = link_to_remove_association f
    .field
      = f.input :quantity
      = f.collection_select :part_id, Part.all, :id, :name, {}, {class: 'select2'}