如何基于许多一对多的关系，选择用户子集？ [英] How to select subset of users based on many-to-many relationship?

问题描述

用户和组织有很多-to-many关联到关系。

一位在相关模型中的变量是一个叫布尔成员。结果
A 用户可以在相关模型多次为用户发生可与多个组织。

我怎样才能从所有的用户选择一个随机的实例：1）没有与任何组织的关系（所以不要在相关模式发生），加上二）用户这确实有关系一个组织，但对他们来说，成员= FALSE 为所有的他们与组织的关系？

我在想是这样的：

 用户= User.where（relationship_id =零|| ???）.offset（兰特（0..100））。第一
 

解决方案

我将做到这一点。

1. User.joins（LEFT JOIN ON relationships.user_id = users.id关系）。在这里（'relationships.user_id IS NULL'）。偏移（兰特（0..100 ））。第一个




2. 是这样的：

     member_ids = Relationship.where（成员：真）.pluck（：USER_ID）.uniq
   用户= User.where.not（ID：member_ids）＃或on Rails的＆LT User.where（'？ID未在（）'，member_ids）; 4
    

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User and Organization have a many-to-many association through Relationship.

One of the variables in the Relationship model is a boolean called member.
A user can occur in the Relationship model multiple times as a user can be related to multiple organizations.

How can I select a random instance from all the users that 1) don't have a relationship with any organization (so don't occur in the Relationship model) plus 2) those users that do have a relationship with an organization but for whom member = false for all their relationships with organizations?

I was thinking of something like:

user = User.where( relationship_id = nil || ??? ).offset(rand(0..100)).first

解决方案

I will do this

1. User.joins("LEFT JOIN relationships ON relationships.user_id = users.id").where('relationships.user_id IS NULL').offset(rand(0..100)).first

2. Something like:

   member_ids = Relationship.where(member: true).pluck(:user_id).uniq
   users = User.where.not(id: member_ids) # or User.where('id NOT in (?)', member_ids) on Rails < 4 
   

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