Question

我有模特

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表包含这些列

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

控制器

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

视图/组/ _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。我知道控制器部分缺少某些东西。我应该在“.build”之后添加一些东西（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

由于您使用的group_artists不仅仅是一个简单的连接表，因此您需要使用nested attributes来创建包含元数据的行：

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

使用不同关联来创建基于乐队成员角色的嵌套记录的结构也不是真正可扩展的 - 对于每个可能的角色，类/表格都会膨胀。

相反，您可能想要使用两个选择：

<%= 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，您无法使用#create方法保存记录。

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

Answer 2

您应该在控制器动作创建

中添加它

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

Group.new不会在数据库中保留模型，但会在保存之后保存。

Answer 3

这些是我需要的增加和改变才能使其发挥作用。

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: proc { |a| a[:artist_id].blank? || a[:role].blank? },
     allow_destroy: true
end

class GroupsController < ApplicationController
  def new
    @group = Group.new
    @group.group_artists.build
    @artists = Artist.all // for a selection
  end
  def create
    @group = Group.new(allowed_params)
    @group.save
  end
end

基团/ _form.html.erb

<%= form_for @group do |f| %>

  <div class="singers">
    <%= f.label :singers %>
    <%= f.fields_for :group_artists do |ga| %>
      <%= ga.collection_select :artist_id, Artist.all, :id, :name %>
      <%= ga.hidden_field :role, value: 'Singer' %>
    <% end %>
  </div>

  <div class="guitarists">
    <%= f.label :guitarists %>
    <%= f.fields_for :group_artists do |ga| %>
      <%= ga.collection_select :artist_id, Artist.all, :id, :name %>
      <%= ga.hidden_field :role, value: 'Guitarist' %>
    <% end %>
  </div>

  <%= f.submit "Submit" %>

<% end %>

如果他的名字在歌手或吉他手中被选中，则你不必指定艺术家的角色。就是这样。感谢max，指导我走向正确的方向。

form_for具有特定关系的模型

3 个答案: