Question

我使用

生成一个表

rails generate model关系follower_id：integer follows_id：integer

然后，我将索引添加如下

class CreateRelationships < ActiveRecord::Migration
  def change
    create_table :relationships do |t|
      t.integer :follower_id
      t.integer :followed_id

      t.timestamps null: false
    end
    add_index :relationships, :follower_id
    add_index :relationships, :followed_id
    add_index :relationships, [:follower_id, :followed_id], unique: true
  end
end

之后我运行了rake db：migrate rake db:migrate

== 20170922165845 CreateRelationships: migrating ==============================

-- create_table(:relationships)

-> 0.0010s

== 20170922165845 CreateRelationships: migrated (0.0011s) =====================

为什么不迁移索引？

schema.rb

ActiveRecord::Schema.define(version: 20170922181915) do 
  #...
  create_table "relationships", force: :cascade do |t| 
    t.datetime "created_at", null: false 
    t.datetime "updated_at", null: false 
  end
  #...
end

Answer 1

我在一个全新的rails（版本4.2和ruby 2.3.4）项目中运行你的命令，一切都按预期工作。我会rake db:rollback并删除文件并再次尝试。

我的步骤：

我跑了rails generate model Relationship follower_id:integer followed_id:integer

然后编辑新创建的迁移以添加索引，如下所示：

class CreateRelationships < ActiveRecord::Migration
  def change
    create_table :relationships do |t|
      t.integer :follower_id
      t.integer :followed_id

      t.timestamps null: false
    end
    add_index :relationships, :follower_id
    add_index :relationships, :followed_id
    add_index :relationships, [:follower_id, :followed_id], unique: true
  end
end

跑了rake db:migrate 打开schema.rb并注意索引在create_table块之外：

# encoding: UTF-8
# This file is auto-generated from the current state of the database. Instead
# of editing this file, please use the migrations feature of Active Record to
# incrementally modify your database, and then regenerate this schema definition.
#
# Note that this schema.rb definition is the authoritative source for your
# database schema. If you need to create the application database on another
# system, you should be using db:schema:load, not running all the migrations
# from scratch. The latter is a flawed and unsustainable approach (the more migrations
# you'll amass, the slower it'll run and the greater likelihood for issues).
#
# It's strongly recommended that you check this file into your version control system.

ActiveRecord::Schema.define(version: 20170922191347) do

  create_table "relationships", force: :cascade do |t|
    t.integer  "follower_id"
    t.integer  "followed_id"
    t.datetime "created_at",  null: false
    t.datetime "updated_at",  null: false
  end

  add_index "relationships", ["followed_id"], name: "index_relationships_on_followed_id"
  add_index "relationships", ["follower_id", "followed_id"], name: "index_relationships_on_follower_id_and_followed_id", unique: true
  add_index "relationships", ["follower_id"], name: "index_relationships_on_follower_id"

end

为什么我无法将索引迁移到我的数据库方案

1 个答案: