为什么Rails 5更改了“索引"?到“外键"? [英] Why did Rails 5 changed "index" to "foreign key"?

问题描述

如果您在Rails 4中有此功能:

If you had this in Rails 4:

t.references :event, index: true

现在您可以在Rails 5中使用foreign_key代替index.我不太明白为什么他们决定这样做，因为功能保持不变，您要添加的是INDEX，而不是该列的外键.

Now you could use foreign_key instead of index in Rails 5. I don't quite understand WHY they decided to do this, since the functionality remains the same, what you're adding is an INDEX, not a FOREIGN KEY to that column.

推荐答案

在Rails 5中-当我们引用模型时，会自动创建foreign_key上的索引.

In Rails 5 - when we reference a model, index on the foreign_key is automatically created.

迁移API在Rails 5中已更改-

Migration API has changed in Rails 5 -

Rails 5更改了迁移API，因此，即使在运行迁移时未将null: false选项传递给时间戳，也不会为时间戳自动添加非null.

Rails 5 has changed migration API because of which even though null: false options is not passed to timestamps when migrations are run then not null is automatically added for timestamps.

类似地，几乎在所有情况下，我们都希望为被引用的列创建索引.因此，Rails 5不需要引用即可具有index: true.运行迁移后，会自动创建索引.

Similarly, we want indexes for referenced columns in almost all cases. So Rails 5 does not need references to have index: true. When migrations are run then index is automatically created.

例如-(从 http://blog.bigbinary.com/2016/03/01/migrations-are-versioned-in-rails-5.html )

当您运行rails g model Task user:references

路轨4会生成

class CreateTasks < ActiveRecord::Migration
  def change
    create_table :tasks do |t|
      t.references :user, index: true, foreign_key: true
      t.timestamps null: false
    end
  end
end

Rails 5会生成

And rails 5 would generate

class CreateTasks < ActiveRecord::Migration[5.0]
  def change
    create_table :tasks do |t|
      t.references :user, foreign_key: true
      t.timestamps
    end
  end
end

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