Grails/GORM:belongsTo在1:N关系中的含义

Question

在普通的一对多映射中,"一"侧是该关联的所有者.为什么有人会使用belongsTo-mapping进行这样的映射？我错过了指定belongsTo的一些副作用吗？

换句话说:在GORM中指定belongsTo-mapping而不是指定它会产生什么影响？

Answer 1

是否指定belongsTo取决于所需的引用操作的类型.

如果你想让Grails做删除,CASCADE参考动作,那么DO指定belongsTo.如果你想让Grails做删除,RESTRICT参考动作,那么不要指定belongsTo.

例如

// "belongsTo" makes sense for me here. 
class Country {
  String name
  static hasMany = [states:State]
}

class State {
  String name;
  // I want all states to be deleted when a country is deleted. 
  static belongsTo = Country
}

// Another example, belongsTo doesn't make sense here
class Team {
  String name
  static hasMany = [players:Player]
}

class Player {
   String name
   // I want that a team should not be allowed to be deleted if it has any players, so no "belongsTo" here. 
}

希望这可以帮助.