ruby-on-rails - Ruby on Rails 重复列名 : user_id: ALTER TABLE "articles" ADD "user_id" integer

Question

我不断收到错误消息:-- add_column(:articles, :user_id, :integer) rake 中止!StandardError:发生错误，此迁移和所有后续迁移均已取消:

SQLite3::SQLException: 重复列名: user_id: ALTER TABLE "articles"ADD "user_id"integer

这是我所做的所有迁移:

 class AddUserIdToArticles < ActiveRecord::Migration
  def change
    add_column :articles, :user_id, :integer
  end
end

---

class CreateUsers < ActiveRecord::Migration
  def change
    create_table :users do |t|
        t.string :username
        t.string :email
        t.timestamps
    end
  end
end

---

class AddDescriptionToArticles < ActiveRecord::Migration
  def change
    add_column :articles, :description, :text
    add_column :articles, :created_at, :datetime
    add_column :articles, :updated_at, :datetime
  end
end

---

class CreateArticles < ActiveRecord::Migration
  def change
    create_table :articles do |t|
      t.string :title
    end
  end
end

---

Answer 1

出现错误

class AddUserIdToArticles < ActiveRecord::Migration
  def change
    add_column :articles, :user_id, :integer
  end
end

因为 user_id 列已经存在于表 articles 中

您可以通过将代码更改为:

class AddUserIdToArticles < ActiveRecord::Migration
  def change
    unless column_exists? :articles, :user_id
      add_column :articles, :user_id, :integer
    end
  end
end

但我不建议这样做，该列一开始就不应该存在，或者您只是想添加一个已经存在的列。

顺便说一句，我建议为你的外键添加一个索引，比如 user_id