为Active Record中的add_column和add_index添加唯一：true

Even though my application isn't gonna allow a user to key in a location, I wanted to enforce a uniqueness on city in the database. Since my Rails app will be searching on the city column, I would like to add an index on the city column as well but was wondering if it matters adding unique: true on the index as well. Is this repetitive? If this doesn't make sense, I would really appreciate it if you could explain why.

即使我的应用程序不允许用户键入某个位置，我也希望在数据库中强制执行城市的唯一性。由于我的Rails应用程序将在city列上搜索，我想在city列上添加一个索引，但是想知道是否重要的是添加唯一：true也在索引上。这是重复吗？如果这没有意义，如果你能解释原因我真的很感激。

class CreateLocations < ActiveRecord::Migration
  def change
    create_table :locations do |t|
      t.string :city, unique: true
      t.string :state

      t.timestamps
    end

    add_index :locations, :city, unique: true
  end
end

3 个解决方案

#1

As far as I know the unique option in the create_table block is actually not supported and doesn't do anything, see TableDefinition. To create the unique index, you need to call the method add_index the way you do now. Note that a unique index is both for uniqueness and for searching etc., there's no need to add two indexes on the same column.

据我所知，create_table块中的唯一选项实际上不受支持且不执行任何操作，请参阅TableDefinition。要创建唯一索引，您需要按照现在的方式调用方法add_index。请注意，唯一索引既可用于唯一性，也可用于搜索等，无需在同一列上添加两个索引。

#2

Using Rails 4, you can provide: index param a hash argument

使用Rails 4，您可以提供：index param hash参数

class CreateLocations < ActiveRecord::Migration
  def change
    create_table :locations do |t|
      t.string :city, index: { unique: true}
      t.string :state

      t.timestamps
    end
  end
end

#3

You can specify unique index while scaffolding:

您可以在scaffolding中指定唯一索引：

rails generate model Locations city:string:uniq state:string

This will create Model, Spec, Factory and this migration:

这将创建Model，Spec，Factory和此迁移：

class CreateLocations < ActiveRecord::Migration
  def change
    create_table :locations do |t|
      t.string :city
      t.string :state

      t.timestamps null: false
    end
    add_index :locations, :city, unique: true
  end
end

Rails knows what it's doing - nothing more is required.

Rails知道它正在做什么 - 不再需要了。

#1

#2