如何在Grails中搜索集合中包含另一个元素的元素？ [英] How do I search for elements whose collection contains another element in Grails?

问题描述

假设我有一个名为User的域类，可以跟随其他User对象。它有这样的字段指定为：

Let's say I have a domain class called "User" which can follow other "User" objects. It does so having a field specified as:

def hasMany=[followedUsers:User]

我需要做相反的操作（找到跟随特定User对象的所有User对象），而不设置反向关系，因为它不是用例经常执行。我试图这样做，使用闭包：

I need to do the reverse (find all User objects that follow a specific User object) without setting up the reverse relationship, since it is not a use case performed often. I tried to do something like this, using closures:

User.findAll { it.followedUsers.contains(userInstance) }

，但这始终会返回数据库中的所有用户，我尝试使用HQL，但也失败了。

but this always returns all users in the database, regardless of their follow status. I tried doing with HQL but failed miserably as well.

任何人都可以给我一个简单的方法来实现这一点的一个快速指针？谢谢。

Could anyone give me a quick pointer on the simplest way to accomplish this? Thank you.

推荐答案

您可以使用此HQL查询：

You can use this HQL query:

User.executeQuery(
   'select u from User u where :follower in elements(u.followedUsers)',
   [follower: userInstance])

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