Spring Grails-GORM中的树状结构

我想在Grails GORM中创建一个树状结构。该结构应为其他物体的容器，并应完全满足以下要求：

• 一个节点应该有0到n个子节点
• 一个节点应该只有一个父节点
• 节点应具有0到n个同级节点

如何在Grails GORM中定义这样的结构

我尝试了以下课程：

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()
    }
}

但在启动时，我得到以下错误：

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

---

树通常每个节点有一个父节点。您可以定义与自身具有一对多关系的树节点，如下所示：

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']
}

如果它有多个父母，它实际上不是计算机科学意义上的树。这种数据结构通常称为有向图。您可以将其建模为与自身的多对多关系，如下所示：

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']
}

---

阿泰洛是对的。要描述关系，必须使用2个域类：

class Node {
    static hasMany = [relations: Relation]
}
class Relation {
    Node fromNode
    Node toNode
    String name //ex. 'son'
    String reverseName // ex. 'father'
}

---

如何插入和删除节点？如何扩展与属性（如dateCreated）的关系？插入和删除，与任何其他grails域对象相同。在

GraphNode

示例中，调用

node.addToParents（parent）

或

node.addToChildren（child）

在保存前添加父级或子级。如果希望关系本身具有属性，最好将关系建模为单独的实体，例如，

GraphNode

和

GraphEdge

。添加

mappedBy

告诉gorm

children

是通过

parent

映射的。这不起作用，因为我的类与您发布的不同。将此添加到您发布的类：

static mappedBy=[children:'parent']

。@tim_yates的可能重复并非同一主题的每个问题都是重复的！我认为，您需要添加'static belongsTo=[parent:TreeNode]'