如何在Grails中實現自引用關係？

Question

考慮以下用戶等級：

class User { 

    String name 

    static hasMany = [friends: User] 
} 

我想，一個用戶可以有很多朋友是哪個用戶正在訪問的類的實例。

如何實現用戶的好友關係？

Answer 1

1.你是如何定義的relathionship

 class User { 
     static hasMany = [ friends: User ] 
     static mappedBy = [ friends: 'friends' ] //this how you refer to it using GORM as well as Database 
     String name 

     String toString() { 
      name 
     } 
     def static constrains() { 
      name(nullable:false,required:true) 

     } 
    def static mapping={ 
    // further database custom mappings ,like custom ID field/generation 
    } 
    } 

2.How保存數據：

def init = {servletContext-> 

if(User?.list()==null) { // you need to import User class :) 
def user = new User(name:"danielad") 
def friends= new User(name:'confile') 
def friends2=new User(name:'stackoverflow.com') 
user.addToFriends(friends) 
user.addToFriends(friends2) 
user.save(flash:true) 
} 
} 

3＃。您的問題在這個堆棧溢出鏈接上重複： Maintaining both sides of self-referential many-to-many relationship in Grails domain object

Answer 2

它看起來像多對多關係（一個用戶有很多朋友，並且是很多用戶的朋友）。所以其中一個解決方案就是創建新的域名類，讓它說成是Frendship。然後修改用戶領域類喜歡這裏：

class Friendship { 
    belongsTo = [ 
     friend1: User 
     , friend2: User 
    ] 
} 

class User{ 
    String name 
    hasMany = [ 
     hasFriends: Friendship 
     , isFriendOf: Friendship 
    ] 

    static mappedBy = [ 
      hasFriends: 'friend1' 
      , isFriendOf: 'frined2' 
    ] 
}