屬於多個域

Question

我有4類，事件，問題，請求和另一個是附件。

每個域的樣子.........

Class Incidents 
    { 
    // other fields 
     static hasOne = [attachment: Attachment] 

     static constraints = [attachment nullable:true] 
    } 

    Class Problems 
    { 
    // other fields 
     static hasOne = [attachment: Attachment] 

     static constraints = [attachment nullable:true] 
    } 

    Class Requests 
    { 
    // other fields 
     static hasOne = [attachment: Attachment] 

     static constraints = [attachment nullable:true] 
    } 

    Class Attachment 
    { 
    // other fields 
     static belongsTo= [ 
        incident: Incidents, 
        problem: Problems, 
        requests: Requests 
] 

    static constraints = { 
     incident nullable: true 
     problem nullable: true 
     requests nullable: true 
} 

當我節省事件的對象

，它會引發像列「PROBLEM_ID」不能爲空例外。 該怎麼辦？

Answer 1

嘗試使用

Attachment attachment 
    static constraints = {attachment: unique: true, nullable:true}  
    static mapping = { 
    attachment cascade: "delete" 
    }