带有活动记录的 Rails 排除查询 -- Rails 3.1 [英] Rails exclusion query with active record -- Rails 3.1

问题描述

在这种情况下我将如何使用活动记录:

How would I use active record in this case:

我有两个表:用户、管理员

I have two tables: Users, Admins

管理员也可以是用户，因此他们的表中有一个 user_id.

Admins can be users also and thus have a user_id in their table.

我想选择所有没有在 admins 表中设置 user_id 的用户

注意:这只是一个示例.如果这是一个真实的案例，那么我当然不会为用户和管理员提供两个不同的表.

NOTE: This is just an example case. If this was a real case then of course I wouldn't have two different tables for users and admins.

再一次，我知道这样做的语义是糟糕的数据库设计——但这只是一个假案例.

Again, I know the semantics of doing it like this is terrible db design -- but it's just an dummy case.

推荐答案

你可以使用 :conditions 来包含一个 NOT IN:

You can use :conditions to include a NOT IN:

User.find(:all, :conditions => ['user_id not in (?)', @admins.map( &:id )])

<小时>

OR 您可以将其编码到用户的 scope(也称为 Rails 3.x 之前的 named_scope )中:

---

OR you can code it into a User's scope ( a.k.a. named_scope prior to Rails 3.x ):

class User < ActiveRecord::Base
  scope :not_admin, lambda { |admins| { :conditions => ['user_id not in (?)', admins.select( &:id ).join( ',' )] }
end

并将其用作:

User.not_admin( @admins )

<小时>

OR 为了不依赖于传递的 @admins 变量，您可以使用 joins:

---

OR in order not to depend on @admins variable being passed you can use joins:

class User < ActiveRecord::Base
  scope :not_admin, joins( :admin ).where( :admins => { :user_id => nil } )
end

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