Rails 4，通过连接表在has_many中指定自定义外键？答案

【问题标题】：Rails 4, specify custom foreign key in has_many through join table?Rails 4，通过连接表在has_many中指定自定义外键？
【发布时间】：2016-07-20 01:13:48
【问题描述】：

我想在我的 rails 4 应用程序中为 has_many through 关联在连接表中指定一个自定义外键。请看下面，我到目前为止...

当我在 Rails 控制台中执行 user.team_memberships.create 时，我收到此错误：

ActiveRecord::UnknownAttributeError: unknown attribute 'user_id' for TeamMembership.

users.rb

class User < ActiveRecord::Base
    has_many :team_memberships
    has_many :teams, through: :team_memberships

teams.rb

class Team < ActiveRecord::Base
    has_many :team_memberships
    has_many :members, through: :team_memberships

team_membership.rb

    class TeamMembership < ActiveRecord::Base
      belongs_to :member, class_name: 'User', foreign_key: 'member_id'
      belongs_to :team

schema.rb

create_table "team_memberships", force: :cascade do |t|
    t.integer  "member_id"
    t.integer  "team_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

  add_index "team_memberships", ["member_id"], name: "index_team_memberships_on_member_id", using: :btree
  add_index "team_memberships", ["team_id"], name: "index_team_memberships_on_team_id", using: :btree

  create_table "teams", force: :cascade do |t|
    t.string   "name"
    t.integer  "team_snap_id"
    t.datetime "created_at",   null: false
    t.datetime "updated_at",   null: false
  end

  create_table "users", force: :cascade do |t|
    t.string   "email",                  default: "", null: false
    t.string   "encrypted_password",     default: "", null: false
    t.string   "reset_password_token"
    t.datetime "reset_password_sent_at"
    t.datetime "remember_created_at"
    t.integer  "sign_in_count",          default: 0,  null: false
    t.datetime "current_sign_in_at"
    t.datetime "last_sign_in_at"
    t.inet     "current_sign_in_ip"
    t.inet     "last_sign_in_ip"
    t.datetime "created_at",                          null: false
    t.datetime "updated_at",                          null: false
    t.string   "name"
    t.integer  "teamsnap_uid"
    t.string   "teamsnap_access_token"
  end

【问题讨论】：

当您在User 和Team 上将foreign_key 添加到has_many :through 关系时发生了什么？

标签： ruby-on-rails foreign-keys associations has-many-through

【解决方案1】：

您需要将foreign_key: 'member_id' 添加到User 上的has_many 声明中。您还可以删除TeamMembership 中belongs_to 上的foreign_key 选项——Rails 会自动推断。

用户.rb

class User < ActiveRecord::Base
  has_many :team_memberships, foreign_key: 'member_id'
  has_many :teams, through: :team_memberships

team_membership.rb

class TeamMembership < ActiveRecord::Base
  belongs_to :member, class_name: 'User'
  belongs_to :team

【讨论】：

【解决方案2】：

您需要在两个模型中指定外键

class User < ActiveRecord::Base
  has_many :team_memberships, foreign_key: 'member_id'
  has_many :teams, through: :team_memberships
end

和

class TeamMembership < ActiveRecord::Base
  belongs_to :member, class_name: 'User', foreign_key: 'member_id'
  belongs_to :team
end

如果您没有在用户模型中添加外键，那么您将无法为用户创建团队成员，同样如果您不在团队成员中指定外键，那么您将无法获得团队成员的用户。

【讨论】：