数据库多层数据运用递归算法生成树形数据

妖狐艹你老母 2022-06-13 03:50 140阅读 0赞

第一步：准备表结构及对应的表数据

1.表结构

create table City  
(  
id char(32) not null,  
name varchar2(30),  
parent\_id char(32) //父级字段  
)

2.插入数据

insert into City (id, name, parent\_id) values (1, '书籍', 0);  
insert into City (id, name, parent\_id) values (2, '科普书籍', 1);  
insert into City (id, name, parent\_id) values (3, '教科书籍', 1);  
insert into City (id, name, parent\_id) values (4, '童话书籍', 1);  
insert into City (id, name, parent\_id) values (5, '语文', 3);  
insert into City (id, name, parent\_id) values (6, '数学', 3);  
insert into City (id, name, parent\_id) values (7, '九年级上册语文书', 5);  
insert into City (id, name, parent\_id) values (8, '九年级下册语文书', 5);  
insert into City (id, name, parent\_id) values (9, '九年级上册数学书', 6);  
insert into City (id, name, parent\_id) values (10, '九年级下册数学书', 6);  
insert into City (id, name, parent\_id) values (11, '十万个为什么', 2);  
insert into City (id, name, parent\_id) values (12, '格林童话', 4);

第二步：建立Entity的Bean对象

1.建立Bean

public class CityEntity  implements Serializable \{  
private String id;  
private String name;  
private String parent\_id;  
  
//getter，setter  
\}

2.建立对外输出的响应Bean

public class CityResponse \{  
    private String id;  
    private String name;  
    private String parent\_id;  
    private List children = new ArrayList();  
  
    //getter，setter  
    public CityResponse() \{  
    \}  
  
    public CityResponse(CityEntity entity) \{  
        this.set(entity);  
    \}  
  
    public CityResponse set(CityEntity entity) \{  
        this.id = entity.getId;  
        this.name = entity.getName;  
        this.parentId = entity.getParentId;  
  
        return this;  
    \}  
\}  
  
第三步 进行递归遍历，生成树形接口

1.测试代码：

public class CityTest \{  
@Test  
public void cityTree() throws Exception\{  
System.out.println(recursiveTree(1));  
\}

2.递归方法

public CityResponse getTreeModule(String id) throws Exception \{  
        CityResponse firstTreeResponse = new CityResponse();  
        //根据id获取节点对象(SELECT \* FROM City c WHERE c.id=?)  
        CityEntity entity = cityService.findById(id);  
        firstTreeResponse.set(entity);  
        //查询id下的所有子节点(SELECT \* FROM City c WHERE c.parent\_id=?)  
        List<CityEntity> entities = cityService.findByParentId(id);  
        List<CityResponse> treeResponses = new ArrayList<CityResponse>();  
        CityResponse secondTreeResponse = null;  
        for (CityEntity cityEntity : entities) \{  
            secondTreeResponse = new CityResponse();  
            treeResponses.add(secondTreeResponse.set(CityEntity));  
        \}  
        CityResponse cityTreeResponse = null;  
        for (CityResponse child : treeResponses) \{  
             cityTreeResponse = getTreeModule(child.getId());//开始递归  
            firstTreeResponse.getChildren().add(cityTreeResponse);  
        \}  
        return firstTreeResponse;  
    \}  
  
3.输出(省略)