如何覆盖addTo *和RemoveFrom * GORM / Grails方法？ [英] How to override addTo* and RemoveFrom* GORM/Grails methods?

问题描述

我试图覆盖Grails / GORM提供的动态方法addTo *，但它似乎不起作用。

以下是代码：

  class Match {
 static hasMany = [players：Player，matchPlayers：MatchPlayer] 
 
 void addToPlayers（玩家玩家）{
 if（players.add（player））{
 MatchPlayer matchPlayer = new MatchPlayer（match：this，player：player）
 matchPlayers.add（matchPlayer）
 } 
 
 $ b $ ma = new Match（）。save（）
 ma.addToPlayers（player1）
  

问题是，当调用addToPlayers时，我得到以下异常：

  java.lang.NullPointerException：无法在null对象上调用方法add（）
  

所以基本上看来，我必须自己初始化集合'玩家'。

好吧，在这之前，我想对GORM机制有一些见解：

1 - GORM集合的默认实现是什么（我知道它是java.util.Set的实现，但是哪一个实现？）

2 - 是否正确（通过重写addToPlayers方法）？ （我唯一需要的是每次在匹配实例中添加/删除玩家时创建/删除MatchPlayer对象）。如果是，为什么我有例外？你有更好的设计吗？

谢谢。

解决方案

您的代码与标准Grails方法类似，请参阅org.codehaus.groovy.grails.pluginsDomainClassGrailsPlugin.addRelationshipManagementMethods（）中的代码。如果不指定集合的​​类型，则初始的Set实现是HashSet，如果指定SortedSet，则为TreeSet，例如

  static hasMany = [players：Player，matchPlayers：MatchPlayer] 
 SortedSet players 
  

I tried to override the dynamic method addTo* provided by Grails/GORM but it doesn't seem to work.

Here is the code :

class Match {
    static hasMany = [players: Player, matchPlayers: MatchPlayer]

    void addToPlayers(Player player) {
        if (players.add(player)) {
            MatchPlayer matchPlayer = new MatchPlayer(match: this, player: player)
            matchPlayers.add(matchPlayer)
        }
    }
}
ma = new Match().save()
ma.addToPlayers(player1)

The issue is that when calling addToPlayers I got the following exception:

java.lang.NullPointerException: Cannot invoke method add() on null object

So basically it seems that I have to initialize myself the collection 'players'.

Well, before doing that, I would like to have some insights on GORM mechanism :

1 - What is the default implementation for collections in GORM (I know that it is an implementation of java.util.Set but which one?)

2 - Is it the right thing to do (by overriding the addToPlayers method) ? (My only need is to create/remove an object MatchPlayer each time a player is added/removed in the match instance). If yes, why do I have an exception? Do you have a better design for this?

Thank you.

解决方案

Your code is similar to the standard Grails approach, see the code for this in org.codehaus.groovy.grails.pluginsDomainClassGrailsPlugin.addRelationshipManagementMethods(). The initial Set implementation is either a HashSet if you don't specify the type of the collection, or a TreeSet if specify a SortedSet, e.g.

static hasMany = [players: Player, matchPlayers: MatchPlayer]
SortedSet players

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