Rails与具有嵌套属性的表单的关联问题

Question

I have the following models in my application:

User:

class User < ApplicationRecord
  # Include default devise modules. Others available are:
  # :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable

  before_destroy { roles.clear }

  has_many :users_roles
  has_many :roles, through: :users_roles

  accepts_nested_attributes_for :roles
  #accepts_nested_attributes_for :user_extras

  #id :confirmable is activated
  def confirmation_required?
    false
  end
end

Role:

class Role < ApplicationRecord
  #before_destroy { users.clear }

  has_many :users, through: :users_roles

end

and UserRoles:

class UsersRoles < ApplicationRecord
  belongs_to :user
  belongs_to :role
end

I also have a form that will accept nested attributes, which looks something like this:

<%= form_for(resource, as: resource_name, url: registration_path(resource_name)) do |f| %>
  <%= devise_error_messages! %>

  <div class="field">
    <%= f.label :email %><br />
    <%= f.email_field :email, autofocus: true %>
  </div>

  <div class="field">
    <%= f.label :password %>
    <% if @minimum_password_length %>
    <em>(<%= @minimum_password_length %> characters minimum)</em>
    <% end %><br />
    <%= f.password_field :password, autocomplete: "off" %>
  </div>

  <div class="field">
    <%= f.label :password_confirmation %><br />
    <%= f.password_field :password_confirmation, autocomplete: "off" %>
  </div>

  <div class="field">
    <%= f.label :password_confirmation %><br />
    <%= f.password_field :password_confirmation, autocomplete: "off" %>
  </div>

  <%= f.fields_for :roles do |field| %>
    <%= field.label :name %></div>
    <%= field.text_field :name %>
  <% end %>

  <div class="actions">
    <%= f.submit "Sign up" %>
  </div>
<% end %>

Also I have a controller that renders this form:

class Admin::AccountController < ApplicationController
  before_action :authenticate_user!

  layout "admin/layouts/dashboard"

  def index
    @resource = User.new
    @resource2 = Role.new
    @resource.roles << @resource2 


    p "==================="
    p @resource
    p @resource2
    p "==================="
    @resource.roles.build

    # respond_to do |format|
    #   format.html
    #   format.json { render json: @resource }
    # end

  end

  private

    def admin_account_params
      params.require(:resource).permit(:email, :password, :password_confirmation, roles_attributes: [ :name ])
    end
end

The thing is when I visit the page, I get the following error:

uninitialized constant User::UsersRole

Extracted source (around line #9):
7
8
9
10
11
12

    @resource = User.new
    @resource2 = Role.new
    @resource.roles << @resource2 


    p "==================="

I am not sure what is wrong with this at the moment. It will be great if you can spot the problem. Many thanks in advance.

Answer 1

Model classes by convention should be singular so the model class name should be...

class UsersRole < ApplicationRecord
  belongs_to :user
  belongs_to :role
end

This will automatically map to a database table named users_roles

If you insist on using a plural class name then you need to specify the class name explicitly

has_many :users_roles, class_name: 'UsersRoles'

And you'll need this in both the User model and the Role model