ruby-on-rails - 具有特定关系的 form_for 模型

Question

我有
模型

class Group < ApplicationRecord
  has_many :group_artists
  has_many :singers, -> { where role: "Singer" }, class_name: "GroupArtist"
  has_many :guitarists, -> { where role: "Guitarist" }, class_name: "GroupArtist"
end

class GroupArtist < ApplicationRecord
  belongs_to :group
  belongs_to :artist
end

class Artist < ApplicationRecord
  has_many :group_artists
  has_many :groups, through: :group_artists
end

group_artists 表有这些列

class CreateGroupArtists < ActiveRecord::Migration[5.1]
  def change
    create_table :group_artists, id: false do |t|
      t.references :group, foreign_key: true, null: false
      t.references :artist, foreign_key: true, null: false
      t.string :role
      t.string :acting

      t.timestamps
    end
  end
end

Controller

class GroupsController < ApplicationController
  def new
    @group = Group.new

    @singers = @group.singers.build
    @guitarists = @group.guitarists.build

    @artists = Artist.all // for a selection
  end

  def create
    @group = Group.new(allowed_params)
    @group.save
  end

  private

  def allowed_params
    params.require(:group).permit(:name, :singers, :guitarists, group_artists_attributes: [:group_id, :artist_id, :role, :acting])
  end
end

views/groups/_form.html.erb

<%= form_for @group do |f| %>
  <%= f.label "Singers" %>
  <%= f.fields_for :singers do |singer| %>
    <%= singer.select(:artist_id, @artists.collect { |a| [a.name, a.id.to_i] }, { include_blank: true }) %>
  <% end %>
  <%= f.label "Guitarists" %>
  <%= f.fields_for :guitarists do |guitarist| %>
    <%= guitarist.select(:artist_id, @artists.collect { |a| [a.name, a.id.to_i] }, { include_blank: true }) %>
  <% end %>
  <%= f.submit "Submit" %>
<% end %>

它可以创建组，但不会在 GroupArtist 中创建关系。我知道 Controller 部分缺少某些东西。我应该在“.build”之后添加一些东西，比如(角色:“歌手”)，但它也没有做任何事情。

ruby -v 2.4.1
Rails -v 5.1.3

Answer 1

因为您使用的 group_artists 不仅仅是一个简单的连接表，您需要使用 nested attributes使用元数据创建一行:

class Group < ApplicationRecord
  has_many :group_artists
  has_many :singers, -> { where role: "Singer" }, class_name: "GroupArtist"
  has_many :guitarists, -> { where role: "Guitarist" }, class_name: "GroupArtist"
  accepts_nested_attributes_for :group_artists, 
     reject_if: ->{|a| a[:artist_id].blank? || a[:role].blank?}
end

此外，使用不同的关联来根据乐队成员的角色创建嵌套记录的结构并不是真正可扩展的 - 对于每个可能的角色，类/表单都会膨胀。

相反，您可能想使用两个选择:

<%= form_for @group do |f| %>
  <fields_for :group_artists do |ga| %>
    <div class="field">
      <%= f.label :artist_id, "Artist" %>
      <%= f.collection_select :artist_id, Artist.all, :id, :name %>
      <%= f.label :role %>
      <%= f.select :role, %w[ Singer Guitarist ] %>
    </div>
  <% end %>
  <%= f.submit "Submit" %>
<% end %>

此外，您没有在 #create 方法中保存记录。

def create
  @group = Group.new(allowed_params)
  if @group.save 
    # ...
  else
    render :new
  end
end