业务需求

数据库原本为oracle后转为postgresql（后续简称为pgsql），原本使用start with …connect by prior在pgsql中无法使用，转为RECURSIVE但无法达到前者父子结构排序结果集（需求：查询所有子节点），sql语句转为java代码实现。
需求：打分：小项可打分，小项的父自动计算分数，前端要显示扁平list
界面如下：

开发语言：
springboot+beetsql+vue

oracle实现树结构

1、Controller.java层 ：前端调此处请求

/*** 获取监测指标树形*/@RequestMapping(path = "${mda.model.name}/standard/entity/pjzbtx/lwPjdx/getZbjcpjTreeList", method = RequestMethod.POST)public IPage<LwZbjcpj> getZbjcpjTreeList(@RequestBody PageDTO<LwZbjcpj, LwZbjcpjQuery> request) {return zbjcpjService.getZbjcpjTreeList(request);}

2、service层： 逻辑结构 （zbjcpjService.java），重点：this.entityMapper.queryZbjcpjTree接口

public IPage<LwZbjcpj> getZbjcpjTreeList(PageDTO<LwZbjcpj, LwZbjcpjQuery> request) {Page<LwZbjcpj> page = new Page<>();page.setCurrent(request.getPageNo());page.setSize(request.getPageSize());String pjpcdxId = request.getSimpleCondition().getPjpcdxId();List<LwZbjcpj> zbjcpjTreeList = this.entityMapper.queryZbjcpjTree(pjpcdxId);page.setTotal(zbjcpjTreeList.size());page.setRecords(zbjcpjTreeList);return page;}

3、mapper层：sql语句（数据库交互）(LwZbjcpjMapper.java—接口 )

这里的queryZbjcpjTree接口对应pjpc.md中写的sql语句命名为queryZbjcpjTree

@Mapper
@SqlResource("pjpc")
public interface LwZbjcpjMapper extends BaseExtMapper<LwZbjcpj> {public List<LwZbjcpj>  queryZbjcpjTree(@Param("pjpcdxId") String pjpcdxId);public List<String>  queryZbjcpjParentId(@Param("pjpcdxId") String pjpcdxId, @Param("id") String id);}

4、pjpc.md文件 某业务相关sql语句

queryZbjcpjTree
===
*根据批次对象id查所有子节点
with query as(select zbjc.id,zbjc.pjzb_id,zbjc.pjpcdx_id,mxzb.zbmc,mxzb.sjzb,mxzb.zbcx,zbjc.pjfs,zbjc.xzfs,zbjc.zpfsfrom lw_zbjcpj zbjcleft join lw_pjmxzb mxzbon zbjc.pjzb_id = mxzb.idwhere zbjc.pjpcdx_id = #{pjpcdxId})select t.*, level,CONNECT_BY_ISLEAF AS isleaffrom query tstart with sjzb = '0'connect by prior pjzb_id = sjzbqueryZbjcpjParentId
===
*根据批次对象id和id查所有父节点id
with query as(select zbjc.id,zbjc.pjzb_id,zbjc.pjpcdx_id,mxzb.zbmc,mxzb.sjzb,mxzb.zbcx,zbjc.pjfs,zbjc.xzfs,zbjc.zpfsfrom lw_zbjcpj zbjcleft join lw_pjmxzb mxzbon zbjc.pjzb_id = mxzb.idwhere zbjc.pjpcdx_id =  #{pjpcdxId})
select idfrom querystart with id = #{id}
connect by prior sjzb = pjzb_id

pgsql实现树结构

构造树节点类：尤其重要，树结构,关键属性：
private String id;
private String pid;
private String name;
private List<TreeNode> children;

@Data
@EqualsAndHashCode(callSuper = false)
public class ZbjcpjTreeNode {private String id;private String pjzbId;  // 子private String sjzb; // 父private String zbmc;private String pjfs;private String xzfs;private String zpfs;private int level;private int isleaf;List<ZbjcpjTreeNode> children;
}

1、Controller.java层

/*** 获取监测指标树形*/@RequestMapping(path = "${mda.model.name}/standard/entity/pjzbtx/lwPjdx/getZbjcpjTreeList", method = RequestMethod.POST)public IPage<ZbjcpjTreeNode> getZbjcpjTreeList(@RequestBody PageDTO<LwZbjcpj, LwZbjcpjQuery> request) {return zbjcpjService.getZbjcpjTreeList(request);}

2、service层

解析：getTreeNode把实体类转为有children的树结构；this.entityMapper.queryZbjcpjTreepgsql查回的具有父子关系无树形的结果集；接下来遍历结果集转为树结构（含children的list）;先序遍历树即可得到扁平数据列表
treeToList树转扁平list, flattenTree先序递归，有子则继续遍历

/*** 转为树节点* @param lwZbjcpj* @return*/private ZbjcpjTreeNode getTreeNode(LwZbjcpj lwZbjcpj) {ZbjcpjTreeNode treeNode = new ZbjcpjTreeNode();try {BeanUtils.copyProperties(treeNode, lwZbjcpj);} catch (IllegalAccessException | InvocationTargetException e) {// TODO Auto-generated catch blocke.printStackTrace();}return treeNode;}/*** 根据pjpcdxId查所有子节点  * @param request* @return*/public IPage<ZbjcpjTreeNode> getZbjcpjTreeList(PageDTO<LwZbjcpj, LwZbjcpjQuery> request) {Page<ZbjcpjTreeNode> page = new Page<>();page.setCurrent(request.getPageNo());page.setSize(request.getPageSize());String pjpcdxId = request.getSimpleCondition().getPjpcdxId();List<LwZbjcpj> zbjcpjTreeList = this.entityMapper.queryZbjcpjTree(pjpcdxId);
//	     存储  子元素Map<String, ZbjcpjTreeNode> childMap = new LinkedHashMap<>();for (LwZbjcpj zbjcpj : zbjcpjTreeList) {ZbjcpjTreeNode zbjcNode = this.getTreeNode(zbjcpj);childMap.put(zbjcpj.getPjzbId(), zbjcNode);}//	     树结构List<ZbjcpjTreeNode> tree = new ArrayList<ZbjcpjTreeNode>();for (String zbid: childMap.keySet()) {ZbjcpjTreeNode treeNode = childMap.get(zbid);if (treeNode.getSjzb() == null || "0".equals(treeNode.getSjzb())) { // 根节点tree.add(treeNode);} else { // 子节点ZbjcpjTreeNode parentNode = childMap.get(treeNode.getSjzb());if (parentNode.getChildren()==null) {parentNode.setChildren(new ArrayList<>());}parentNode.getChildren().add(treeNode);}}
//	     将树形结构转换为列表List<ZbjcpjTreeNode> flattenedList = treeToList(tree);page.setTotal(flattenedList.size());page.setRecords(flattenedList);return page;}private List<ZbjcpjTreeNode> treeToList(List<ZbjcpjTreeNode> tree) {List<ZbjcpjTreeNode> flattenedList = new ArrayList<ZbjcpjTreeNode>();for (ZbjcpjTreeNode node:tree) {
//			拉平树flattenTree(node, flattenedList);}return flattenedList;}//	递归先序遍历转为扁平数据结构private void flattenTree(ZbjcpjTreeNode node, List<ZbjcpjTreeNode> flattenedList) {flattenedList.add(node);if (node.getChildren() != null) {for(ZbjcpjTreeNode child:node.getChildren()) {flattenTree(child, flattenedList);}}}

3、mapper层无改变，接口名不修改

4、pjpc.md文件

queryZbjcpjTree与queryZbjcpjParentId两个pgsql语句

queryZbjcpjTree
===
*根据批次对象id查所有子节点  
WITH RECURSIVE query AS (SELECT zbjc.id,zbjc.pjzb_id,zbjc.pjpcdx_id,mxzb.zbmc,mxzb.sjzb,mxzb.zbcx,zbjc.pjfs,zbjc.xzfs,zbjc.zpfsFROM lw_zbjcpj zbjcLEFT JOIN lw_pjmxzb mxzb ON zbjc.pjzb_id = mxzb.idWHERE zbjc.pjpcdx_id = #{pjpcdxId}
),
tree AS (SELECT t.*, 1 AS levelFROM query tWHERE sjzb = '0'UNION ALLSELECT q.*, tree.level + 1FROM query qJOIN tree ON q.sjzb = tree.pjzb_id
)
SELECT tree.*, CASE WHEN EXISTS (SELECT 1 FROM query q WHERE q.sjzb = tree.pjzb_id) THEN 0 ELSE 1 END AS isleafFROM tree;queryZbjcpjParentId
===
*根据批次对象id和id查所有父节点id
WITH RECURSIVE query AS (SELECT zbjc.id,zbjc.pjzb_id,zbjc.pjpcdx_id,mxzb.zbmc,mxzb.sjzb,mxzb.zbcx,zbjc.pjfs,zbjc.xzfs,zbjc.zpfsFROM lw_zbjcpj zbjcLEFT JOIN lw_pjmxzb mxzb ON zbjc.pjzb_id = mxzb.idWHERE zbjc.pjpcdx_id = #{pjpcdxId}
),
tree AS (SELECT id, pjzb_id, sjzbFROM queryWHERE id = #{id}UNION ALLSELECT q.id, q.pjzb_id, q.sjzbFROM query qJOIN tree ON q.pjzb_id = tree.sjzb
)
SELECT id FROM tree;

queryZbjcpjTree的结果集为：level为1在一起，level为2气候，依次往后排，无法达到oracle使用start with…connect by prior就能达到排序的效果，因此使用java代码实现扁平数据树形展示

总结：俩要点，第一：结果集转为带children的树结构；第二：将树转为list扁平结构；算法使用到递归与迭代。

树其他链接

前后端构建侧边栏多级动态导航栏—树形结构