Grails - 将多对多父母/孩子关系映射到单个连接表 [英] Grails - mapping a many-to-many parents/children relation to a single join table

问题描述

我的问题是基于以下（简化的）Grails领域类

  class Dimension {
 
字符串名称
 
 static hasMany = [
 children：Dimension，
 parents：Dimension 
] 
} 
  
 
 
有没有办法将多对多父母/子女关系映射到单个连接表？
解决方案
据我所知，唯一的方法是创建另一个表示父子关系的域类。 
 
 
  class DimensionDependency {
父维度
维度子元素
 $ b $ static属性=维度
} 
 $ b class Dimension {
 static hasMany = [parentDependencies：DimensionDependency] 
 static mappedBy = [parentDependencies：'child'] 
 static mapping = { parentDependencies cascade：'all-delete-orphan'} 
} 
  
  mappedBy 关键字指定引用 DimensionDependency 的对象始终是子对象。通过在映射中指定 all-delete-orphan ，我们确保在从子项中移除 parentDependency 时，关联的 DimensionDependency 将从数据库中删除。
 
 
 
您也可以将便利方法添加到 Dimension 类来封装 DimensionDependencies 上的操作，以使界面更像GORM。
  static transients = ['children'，'parents'] 
 
 Set< Dimension> getChildren（）
 {
 AssignmentDependency.findAllByParent（this）.child 
} 
 
 Set< Dimension> getParents（）
 {
 parentDependencies？.parent？：[] 
} 
 
 Dimension addToParents（Dimension parent）
 {
 if（ ！parentDependencies.find {it.parent == parent& it.child == this}）
 {
 addToParentDependencies（new DimensionDependency（parent：parent，child：this））
 } 
返回此
} 
 
 Dimension removeFromParents（Dimension parent）
 {
 def dep = parentDependencies.find {it.parent == parent} 
 removeFromParentDependencies（dep）
 dep.delete（flush：true）
 return this 
} 
  
我一直在使用这种方法，并且迄今为止没有麻烦。
 
My question is based on the following (simplified) Grails domain class
class Dimension {

    String name

    static hasMany = [
        children: Dimension,
        parents: Dimension
    ]
}
Is there a way to map the many-to-many parents/children relationship to a single join table?
解决方案
As far as I know, the only way to do that is to create another domain class that represents a parent-child relationship.
class DimensionDependency {
  Dimension parent
  Dimension child

  static belongsTo = Dimension
}

class Dimension {
  static hasMany = [parentDependencies: DimensionDependency]
  static mappedBy = [parentDependencies: 'child']
  static mapping = { parentDependencies cascade: 'all-delete-orphan' }
}
The mappedBy keywords specifies that the object refering to a DimensionDependency is always the child. By specifying all-delete-orphan in the mapping, we make sure that when removing a parentDependency from a child, the associated DimensionDependency is deleted from the database.

You may also add convenience methods to your Dimension class to encapsulate operations on DimensionDependencies, to make the interface more GORM-like.
  static transients = ['children', 'parents']

  Set<Dimension> getChildren()
  {
    AssignmentDependency.findAllByParent(this).child
  }

  Set<Dimension> getParents()
  { 
    parentDependencies?.parent ?: []
  }

  Dimension addToParents(Dimension parent)
  {
    if (!parentDependencies.find { it.parent == parent && it.child == this })
    {
      addToParentDependencies(new DimensionDependency(parent: parent, child: this))
    }
    return this
  }

  Dimension removeFromParents(Dimension parent)
  {
    def dep = parentDependencies.find { it.parent == parent }
    removeFromParentDependencies(dep)
    dep.delete(flush: true)
    return this
  }
I've been using this approach for some time and have had no trouble so far.

                        
这篇关于Grails  - 将多对多父母/孩子关系映射到单个连接表的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！