Grails表链接到自己 [英] Grails table that links to itself

问题描述

这篇相关文章提出了一个解决方案，但是我无法完成它的工作： href =https://stackoverflow.com/questions/1787120/grails-domain-class-relationship-to-it-self> Grails领域类本身的关系

有一件事我不明白什么可比较的，并且需要添加一个int compareTo（obj）方法。

将以下内容添加到我的代码中而不实现比较编译，但grails在运行时崩溃：

  // NavMenu父
 SortedSet子项
 static hasMany = [subItems：NavMenu] 
 static belongsTo = [parent：NavMenu] 
 static constraints = {parent（nullable：true）} 
  

在此先感谢

解决方案

当您使用 SortedSet ，内部执行排序算法，但需要排序条件。您需要实现 Comparable 接口，因为这是为内部算法提供排序条件的标准方式。

如果您不需要特定的订单，您可以删除 SortedSet子项行，从而避免执行可比较界面。

I would like to create a grails domain class that links to itself.

This related post suggests a solution but I can't get it to work: Grails domain class relationship to itself

For one thing I don’t understand what comparable does and would need to add a int compareTo(obj) method.

Adding the following to my code without implementing Comparable compiles, but grails crashes at runtime:

//NavMenu parent
SortedSet subItems
static hasMany = [subItems: NavMenu]
static belongsTo = [parent: NavMenu]
static constraints = { parent(nullable:true) }

Thanks in advance

解决方案

When you're using SortedSet, a sort algorithm is internally executed, but it needs a sort criteria. You need to implement the Comparable interface because that is the standard way to provide a sort criteria to the internal algorithm.

If you don't need a specific order, you can delete the SortedSet subItems line and thus avoid implementing the Comparable interface.

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