Ruby on Rails:向现有数据库添加列 [英] Ruby on Rails: adding columns to existing database

问题描述

我遇到错误:

SQLite3::SQLException: no such column: ideas.list_id: 
SELECT "ideas".* FROM "ideas"  
WHERE "ideas"."list_id" = 2

但是我添加了

t.integer :list_id

到我的数据库迁移文件:

to my db migration file:

class CreateIdeas < ActiveRecord::Migration
  def change
    create_table :ideas do |t|
      t.string :name
      t.text :description
      t.string :picture

      t.timestamps
    end
    add_foreign_key :ideas, :lists
  end
end

这给了我:

class CreateIdeas < ActiveRecord::Migration
  def change
    create_table :ideas do |t|
      t.string :name
      t.text :description
      t.string :picture
      t.integer :list_id
      t.timestamps
    end
    add_foreign_key :ideas, :lists
  end
end

然后我输入

rake db:migrate

有什么主意，为什么我会收到一个错误消息，说没有专栏?我还是RoR的新手.我是否必须以其他方式添加列?

Any idea why I would be getting an error saying there's no column? I'm still new to RoRs. Do I have to add a column some other way?

谢谢

推荐答案

如Speransky建议的那样，您永远不要修改旧的迁移文件.而是应创建一个新迁移，以添加所需的列.例如，在这种情况下，您将在应用程序中运行以下命令以创建新的迁移:

As Speransky suggested, you should never modify old migration files. Rather you should create a new migration that adds the desired column. For instance, in this case you would run the following command in your app to create the new migration:

rails generate migration AddListIdColumnToIdeas list_id:integer

然后Rails会自动生成迁移文件，剩下要做的就是运行rake db:migrate.

And Rails would generate the migration file automatically and the only thing left to do is run rake db:migrate.

如果您坚持修改旧的迁移文件，则可以像以前一样添加该列，然后运行以下命令:

If you insist on modifying the old migration file, you can add the column as you did and run the following:

rake db:drop
rake db:create
rake db:migrate

这将销毁您当前的数据库，创建一个新数据库并运行所有迁移(其中将包括您的新列).

Which will destroy your current database, create a new one and run all the migrations (which will include your new column).

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