RoR：ActiveRecord::RecordInvalid：验证失败：参加者必须存在答案

【问题标题】：RoR: ActiveRecord::RecordInvalid: Validation failed: Attendee must existRoR：ActiveRecord::RecordInvalid：验证失败：参加者必须存在
【发布时间】：2020-03-30 18:01:30
【问题描述】：

我正在尝试在 RoR 程序中建立 多对多 关联，但我无法摆脱标题中提到的错误，即我在Rails 控制台是：

User.find(1).attended_events = [Event.find(1)]

我需要解决这个问题，但找不到任何地方，感谢任何帮助。

我的代码：

模型

class User < ApplicationRecord
  has_many :created_events,class_name:"Event"
  has_many :hosts
  has_many :attended_events, through: :hosts
end

class Host < ApplicationRecord
  belongs_to :attended_event, class_name:"Event"
  belongs_to :attendee, class_name:"User"
end

class Event < ApplicationRecord
  belongs_to :creator, foreign_key: :user_id, class_name:'User'
  has_many :hosts
  has_many :attendees, through: :hosts
end

迁移文件

class CreateUsers < ActiveRecord::Migration[6.0]
  def change
    create_table :users do |t|
      t.string :name
      t.string :email

      t.timestamps
    end
  end
end

class CreateHosts < ActiveRecord::Migration[6.0]
  def change
    create_table :hosts do |t|
      t.references :attendee, null: false, foreign_key: true
      t.references :attended_event, null: false, foreign_key: true
      t.integer :user_id
      t.integer :event_id
      t.timestamps
    end
  end
end

class CreateEvents < ActiveRecord::Migration[6.0]
  def change
    create_table :events do |t|
      t.string :date
      t.text :description
      t.references :user, null: false, foreign_key: true

      t.timestamps
    end
  end
end

【问题讨论】：

标签： ruby-on-rails model migration many-to-many associations

【解决方案1】：

了解foreign_key option 的has_many。

class Event < ApplicationRecord
  belongs_to :creator, foreign_key: :user_id, class_name:'User'
  has_many :hosts
  has_many :attendees, through: :hosts
end

这些模型关联是错误的，错误在第二行。

class Event < ApplicationRecord
  belongs_to :creator, foreign_key: :user_id, class_name:'User'
  has_many :hosts
  has_many :attendees, through: :hosts
end

使用这些模型关联，您需要为has_many :hosts 语句指定foreign_key。

class Host < ApplicationRecord
  belongs_to :attended_event, class_name:"Event"
  belongs_to :attendee, class_name:"User"
end

以下是我的建议：

用户

class User < ApplicationRecord
  has_many :created_events, foreign_key: 'user_id'
  has_many :hosts, foreign_key: 'attendee_id'
  has_many :attended_events, through: :hosts
end

主持人

class Host < ApplicationRecord
  belongs_to :attended_event, class_name: 'Event'
  belongs_to :attendee, class_name: 'User'
end

活动

class Event < ApplicationRecord
  belongs_to :creator, class_name: 'User'
  has_many :hosts, foreign_key: 'attended_event_id'
  has_many :attendees, through: :hosts
end

您的主机迁移

最好避免在此处传递foreign_key，它会在数据库中查找attendees 表和attended_events 表。

class CreateHosts < ActiveRecord::Migration[6.0]
  def change
    create_table :hosts do |t|
      # t.references :attendee, null: false, foreign_key: true
      t.references :attendee, null: false
      # t.references :attended_event, null: false, foreign_key: true
      t.references :attended_event, null: false
      t.timestamps
    end
  end
end

【讨论】：

【解决方案2】：

通过关联定义source

class User < ApplicationRecord
  has_many :created_events, class_name:"Event"
  has_many :hosts
  has_many :attended_events, through: :hosts, source: :event
end


class Host < ApplicationRecord
  belongs_to :event
  belongs_to :user
end


class Event < ApplicationRecord
  belongs_to :creator, foreign_key: :user_id, class_name:'User'
  has_many :hosts
  has_many :attendees, through: :hosts, source: :user
end


class CreateHosts < ActiveRecord::Migration[6.0]
  def change
    create_table :hosts do |t|
      t.references :user, null: false, foreign_key: true
      t.references :event, null: false, foreign_key: true

      t.timestamps
    end
  end
end

那你就可以了 User.find(1).attended_events << Event.find(1)

【讨论】：