GORM中的樹結構（grails）

Question

我想在GORM中定義一個樹結構。這裏是我的模型：

class Tree { 
    String name 
    Level rootLevel 

    static hasOne = [rootLevel: Level] 
    static hasMany = [levels: Level] 
    static mappedBy = [levels:"parentTree"] 
} 

class Level { 
    String name 
    Tree parentTree 
    Level parentLevel 
    Set<Level> subLevels 

    static belongsTo = [parentTree: Tree] 
    static hasMany = [subLevels: Level] 
} 

插入似乎工作正常，但是當我無法加載一個具有許多級別和子級別的樹。 我想我錯過了關係中的某些東西： - 樹應該有一個對rootLevel的引用（並且可選地指向所有子元素） -a Level應該引用其父級別，其子級別和全局父樹

你能指出我得到一個像這樣的樹結構的正確方向嗎？ 感謝

Answer 1

我結束了這個解決方案（感謝朋友）：

class Tree { 
    String name 
    Level rootLevel 

    static hasMany = [levels: Level] 
    static mappedBy = [rootLevel: "parentTree", levels: "owningTree"] 

    static constraints = {rootLevel(nullable: true)} 
} 

和

class Level { 
    String name 
    Tree parentTree 
    Tree owningTree 
    Level parentLevel 
    Set<Level> subLevels 

    static belongsTo = [owningTree: Tree, parentLevel: Level] 
    static hasMany = [subLevels: Level] 
    static mappedBy = [parentTree: "rootLevel", owningTree: "levels", subLevels: "parentLevel"] 

    static constraints = { 
     parentTree(nullable: true) 
     parentLevel(nullable: true) 
    } 
} 

我失蹤了樹和水平（owningTree和parentTree）兩者之間的關係和一些的mappedBy配置來幫助休眠。

Answer 2

我不喜歡你的樹結構，所以我創建了自己:)

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() 
    } 
} 

對於確保所有樹節點被裝載，就可以隨時使用急於/非延遲獲取每個treeNode父母和孩子。但是，如果你的樹結構非常大，可能會有性能損失...

至於渴望/懶惰抓取。看看這裏：Using lazy property fetching in Grails/Gorm

Answer 3

The problem is that levels are filled with the parent Tree id, but when you load the Tree, you have the following error "More than one row with the given identifier was found" for the Level class.

你的問題似乎是，你有多個單一的根節點爲每棵樹。這是一種不尋常的方法。要使其正常工作，您必須將實體Tree中的Level rootLevel替換爲Set<Level> roots。