Rails:通过迁移填充现有表 [英] Rails: populate an existing table via a migration

问题描述

假设我在Rails中已有迁移:

Say I have an existing migration in Rails:

class CreateStudies < ActiveRecord::Migration
  def change
    create_table :studies do |t|
      t.string :display_name, null: false
      t.string :tag_name, null: false

      t.timestamps
    end

    add_index :studies, :tag_name, unique: true
  end
end

稍后，我意识到我想在此表中填充许多行，并且我不想使用rake db:rollback或seeds.rb文件.新迁移文件的格式是什么?

Later on I realise that I would like to populate this table with a number of rows and I don't want to use rake db:rollback or the seeds.rb file. What is the format of the new migration file?

推荐答案

刚刚:

在命令提示符下生成:

rails generate migration AddInitialStudies

并修改up和down生成的迁移方法:

And modify up and down method of generated migration:

class AddInitialStudies < ActiveRecord::Migration
  def up
    Study.create(display_name: "Example name", tag_name: "example_name")
  end

  def down
    Study.delete_all
  end
end

目前，我生成了一个Study对象，但是您可以添加任意数量的对象.

At this point I generate one Study object, but you can add as many you want.

在down上，删除在up上添加的记录，因为回滚和再次迁移将复制添加的记录.我假设唯一的研究记录是在up上创建的.注意:tag_name，它必须是唯一的.

On down, remove records added on up, because rollback and migrate again will duplicate added records. I assume the only Study records are the created on up. Take care with :tag_name, which must be unique.

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