PG::UndefinedTable: 错误: 关系“朋友”不存在

Question

我按照本教程来实现好友请求https://dankim.io/mutual-friendship-rails/，第一步是使用好友引用创建好友模型，尽管没有好友表。这确实可以在本地工作，我遵循整个教程并创建和接受所有请求，并且在我尝试推送到 heroku 之前我没有遇到任何问题。我得到的错误是 PG::UndefinedTable: ERROR: 关系“朋友”不存在。

架构：

ActiveRecord::Schema.define(version: 20171217055455) do

  # These are extensions that must be enabled in order to support this database
  enable_extension "plpgsql"

  create_table "comments", force: :cascade do |t|
    t.bigint "post_id"
    t.string "name"
    t.string "body"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.index ["post_id"], name: "index_comments_on_post_id"
  end

  create_table "friend_requests", force: :cascade do |t|
    t.bigint "user_id"
    t.bigint "friend_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.index ["friend_id"], name: "index_friend_requests_on_friend_id"
    t.index ["user_id"], name: "index_friend_requests_on_user_id"
  end

  create_table "friendships", force: :cascade do |t|
    t.bigint "user_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.bigint "friend_id"
    t.index ["friend_id"], name: "index_friendships_on_friend_id"
    t.index ["user_id"], name: "index_friendships_on_user_id"
  end

  create_table "likes", force: :cascade do |t|
    t.bigint "user_id"
    t.bigint "post_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.index ["post_id"], name: "index_likes_on_post_id"
    t.index ["user_id"], name: "index_likes_on_user_id"
  end

  create_table "posts", force: :cascade do |t|
    t.string "body"
    t.bigint "user_id"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.index ["user_id"], name: "index_posts_on_user_id"
  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.index ["email"], name: "index_users_on_email", unique: true
    t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
  end

  create_table "votes", force: :cascade do |t|
    t.string "votable_type"
    t.bigint "votable_id"
    t.string "voter_type"
    t.bigint "voter_id"
    t.boolean "vote_flag"
    t.string "vote_scope"
    t.integer "vote_weight"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.index ["votable_id", "votable_type", "vote_scope"], name: "index_votes_on_votable_id_and_votable_type_and_vote_scope"
    t.index ["votable_type", "votable_id"], name: "index_votes_on_votable_type_and_votable_id"
    t.index ["voter_id", "voter_type", "vote_scope"], name: "index_votes_on_voter_id_and_voter_type_and_vote_scope"
    t.index ["voter_type", "voter_id"], name: "index_votes_on_voter_type_and_voter_id"
  end

  add_foreign_key "comments", "posts"
  add_foreign_key "friend_requests", "users"
  add_foreign_key "friendships", "users"
  add_foreign_key "likes", "posts"
  add_foreign_key "likes", "users"
  add_foreign_key "posts", "users"
end

Answer 1

在本地删除我的数据库并尝试迁移后，我最终遇到了同样的错误。这使我更深入地研究了我的迁移，我发现了我的错误。

迁移导致错误：

class CreateFriendships < ActiveRecord::Migration[5.1]
  def change
    create_table :friendships do |t|
      t.references :user, foreign_key: true
      t.references :friend, foreign_key: true 

      t.timestamps
    end
  end
end

由于没有Friend模型foreign_key:true导致错误。我认为这是因为 foreign_key: true 在 Friend 模型中添加了 belongs_to :friendships 。

class CreateFriendships < ActiveRecord::Migration[5.1]
  def change
    create_table :friendships do |t|
      t.references :user, foreign_key: true
      t.references :friend

      t.timestamps
    end
  end
end

Answer 2

朋友引用需要指定外键的列名。

class CreateFriendships < ActiveRecord::Migration[5.2]
  def change
    create_table :friendships do |t|
      t.references :user, foreign_key: true
      t.references :friend

      t.timestamps
    end
    add_foreign_key :friendships, :users, column: :friend_id
  end
end