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) 耙中止！ StandardError：发生错误，此迁移和所有后续迁移已取消：

SQLite3::SQLException: 列名重复：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

错误开启

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上

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，该列不应该首先存在，或者您只是想添加一个已经存在的列。

顺便说一句，我建议为您的外键添加索引，例如 user_id