我想在Grails GORM中创建一个树状结构。该结构应作为其他对象的容器，并应完全满足以下要求:

Class TreeNode { 
    String name 
    TreeNode parent 
 
    static hasMany = [children: TreeNode] 
 
    //returns the root node, and by extension, the entire tree! 
    TreeNode getRootNode(){ 
       if(parent){ 
          //if parent is not null then by definition this node is a child node of the tree. 
          return parent.getRootNode() 
       }else{ 
          //if parent is null then by definition it is the root node. 
          return this 
       } 
    } 
 
    //you might not need this function, but ill add it as it is common in tree structures 
    boolean isLeaf(){ 
       //determines if this node is a leaf node. a leaf is a node with zero childrens 
       return children.isEmpty() 
    } 
} 

ERROR context.ContextLoader  - Context initialization failed 
Message: Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [children] in class [class test.TreeNode] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [treeNode] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [children:'myprop'] 
    Line | Method 
->>  334 | innerRun  in java.util.concurrent.FutureTask$Sync 
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  
|    166 | run       in java.util.concurrent.FutureTask 
|   1145 | runWorker in java.util.concurrent.ThreadPoolExecutor 
|    615 | run       in java.util.concurrent.ThreadPoolExecutor$Worker 
^    722 | run . . . in java.lang.Thread 
Caused by GrailsDomainException: Property [children] in class [class test.TreeNode] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [treeNode] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [children:'myprop'] 
->>  334 | innerRun  in java.util.concurrent.FutureTask$Sync 
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  
|    166 | run       in java.util.concurrent.FutureTask 
|   1145 | runWorker in java.util.concurrent.ThreadPoolExecutor 
|    615 | run       in java.util.concurrent.ThreadPoolExecutor$Worker 
^    722 | run . . . in java.lang.Thread 
| Error 2013-10-04 17:36:00,730 [localhost-startStop-1] ERROR context.GrailsContextLoader  - Error initializing the application: Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [children] in class [class test.TreeNode] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [treeNode] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [children:'myprop'] 
Message: Error creating bean with name 'pluginManager' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is org.codehaus.groovy.grails.exceptions.GrailsDomainException: Property [children] in class [class test.TreeNode] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [treeNode] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [children:'myprop'] 
    Line | Method 
->>  334 | innerRun  in java.util.concurrent.FutureTask$Sync 
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  
|    166 | run       in java.util.concurrent.FutureTask 
|   1145 | runWorker in java.util.concurrent.ThreadPoolExecutor 
|    615 | run       in java.util.concurrent.ThreadPoolExecutor$Worker 
^    722 | run . . . in java.lang.Thread 
Caused by GrailsDomainException: Property [children] in class [class test.TreeNode] is a bidirectional one-to-many with two possible properties on the inverse side. Either name one of the properties on other side of the relationship [treeNode] or use the 'mappedBy' static to define the property that the relationship is mapped with. Example: static mappedBy = [children:'myprop'] 
->>  334 | innerRun  in java.util.concurrent.FutureTask$Sync 
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  
|    166 | run       in java.util.concurrent.FutureTask 
|   1145 | runWorker in java.util.concurrent.ThreadPoolExecutor 
|    615 | run       in java.util.concurrent.ThreadPoolExecutor$Worker 
^    722 | run . . . in java.lang.Thread 

请您参考如下方法:

一棵树通常每个节点只有一个父节点。您可以这样定义一个树节点，该树节点与其自身具有一对多的关系:

class TreeNode { 
    TreeNode parent 
    static hasMany = [children: TreeNode] 
    static mappedBy = [children: 'parent'] 
} 

class GraphNode { 
    static hasMany = [children: GraphNode] 
    static hasMany = [parents: GraphNode] 
    static mappedBy = [children: 'parents', parents: 'children'] 
}