3.2 限制深度

查询动态实体

Java

TreeNodeTable table = TreeNodeTable.$;

List<TreeNode> rootNodes = sqlClient
    .createQuery(table)
    .where(table.parentId().isNull())
    .select(
        table.fetch(
            TreeNodeFetcher.$
                .allScalarFields()
                .recursiveChildNodes(
                    cfg -> cfg.depth(2)
                )
        )
    )
    .execute();

Kotlin

val rootNodes = sqlClient
    .createQuery(TreeNode::class) {
        where(table.parentId.isNull())
        select(
            table.fetchBy {
                allScalarFields()
                `childNodes*` {
                    depth(2)
                }
            }
        )
    }
    .execute()

当前被查询的聚合根被规定为第0层，在其基础上向下查询两层子对象，得到如下的数据

[
    {
        "id":1,
        "name":"Home",
        "childNodes":[
            {
                "id":2,
                "name":"Food",
                "childNodes":[
                    {"id":3,"name":"Drinks"},
                    {"id":6,"name":"Bread"}
                ]
            },
            {
                "id":9,
                "name":"Clothing",
                "childNodes":[
                    {"id":10,"name":"Woman"},
                    {"id":18,"name":"Man"}
                ]
            }
        ]
    }
]

信息

最深的4个对象，并非表现为childNodes属性为[]，而是根本没有childNodes属性。

这表示，这4个对象是否有下级对象是未知的，因为递归过程因人为干预而被提前终止。

查询静态DTO

在src/main/dto文件夹下新建任何一个扩展名为dto的文件，编辑代码如下

export com.yourcompany.yourproject.model.TreeNode
    -> package com.yourcompany.yourproject.model.dto

RecursiveTreeNodeView {
    #allScalars(this)
    
    !depth(2)
    childNodes*
}

编译项目，生成Java/Kotlin类型RecursiveTreeNodeView

Java

TreeNodeTable table = TreeNodeTable.$;

List<RecursiveTreeNodeView> rootNodes = sqlClient
    .createQuery(table)
    .where(table.parentId().isNull())
    .select(
        table.fetch(RecursiveTreeNodeView.class)
    )
    .execute();

Kotlin

val rootNodes = sqlClient
    .createQuery(TreeNode::class) {
        where(table.parentId.isNull())
        select(
            table.fetch(RecursiveTreeNodeView::class)
        )
    }
    .execute()

得到如下结果

[
    RecursiveTreeNodeView(
        id=1, 
        name=Home, 
        childNodes=[
            RecursiveTreeNodeView(
                id=9, 
                name=Clothing, 
                childNodes=[
                    RecursiveTreeNodeView(
                        id=18, 
                        name=Man, 
                        childNodes=null
                    ), 
                    RecursiveTreeNodeView(
                        id=10, 
                        name=Woman, 
                        childNodes=null
                    )
                ]
            ), 
            RecursiveTreeNodeView(
                id=2, 
                name=Food, 
                childNodes=[
                    RecursiveTreeNodeView(
                        id=6, 
                        name=Bread, 
                        childNodes=null
                    ), 
                    RecursiveTreeNodeView(
                        id=3, 
                        name=Drinks, 
                        childNodes=null
                    )
                ]
            )
        ]
    )
]