关联belongs_to vs嵌套形式的属性

Question

I have a situation like below:

class User < ActiveRecord::Base
  belongs_to :user_group
  accepts_nested_attributes_for :user_group
end

class UserGroup < ActiveRecord::Base
  has_many :users
end

Controller:

UsersController < ApplicationControler
  def new
    @user = User.new
    @user.build_user_group
  end

  def create
    @user = User.new(user_params)

    if @user.save
      # do something
    else
      # do something
    end
  end

  private

  def user_params
    params.require(:user).permit(:email, :username, user_group_attributes: [:name])
  end
end

Form:

= simple_form_for @user do |f|
            = f.input :username
            = f.simple_fields_for :user_group do |builder|
              = builder.input :name, collection: UserGroup.all.map(&:name), prompt: "Choose one"
            = f.input :email
            = f.button :submit, 'Create', class: 'btn btn-success'

But it doesn't create an user with the association between the user and the user_group. UserGroup table is just a list of user groups, eg moderator, user and so on. So I need to select a group in the form and create a new user with association. What am I doing wrong? Do I need to find a group in create action and pass it as @user.user_group = the_chosen_group ?

PS Is it a proper name convention of UserGroup? Maybe should I call it as Group?

Regards.

Answer 1

Nested attributes should only be used when you want to allow editing of associated object via object itself. In short, every time you submit the form you created, rails will receive params like:

{ username: 'sth', user_group_attributes: { name: 'Group name' }

When you assign attributes like this, rails will create new attribute group, as it has no idea it is to search for such a group.

Since you only want to assign given user to usergrooup, you do not need nested_attributes at all. All you need is:

= simple_form_for @user do |f|
  = f.input :username
  = f.input :user_group_id, collection: UserGroup.all.pluck(:name, :id), prompt: 'Choose one'
  = f.input :email
  = f.button :submit, 'Create', class: 'btn btn-success'

And in the controller:

def user_params
  params.require(:user).permit(:email, :username, :user_group_id)
end