MybatisPlus实现对象嵌套关联查询一对多List集合查询

目录
对象嵌套关联查询一对多List集合查询
mybatis嵌套关联查询如下
一对多查询(经典案例)
条件
数据库
代码实现

对象嵌套关联查询一对多List集合查询

mybatis嵌套关联查询如下
由于我的是一对集合查询，所以我有两个类。
@Data@TableName("tb_user")public class User { @TableId(type= IdType.INPUT) private String id; @TableField("user_name") private String username; private String password; private String name; private String email; private int age; private ArrayList<Authority> list;}
权限类
@Data@TableNamepublic class Authority { @TableId(type = IdType.INPUT) @TableField("aid") private int id; @TableId("aname") private String name;}
测试类
@Test public void ManyToMany(){ User user = userMapper.selectAuthorityById(1); ArrayList <Authority> list = user.getList(); System.out.println(user); for (Authority authority : list) { System.out.println("所对应权限为"+authority.getName()); } }
springboot项目的依赖
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter</artifactId> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.26</version> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <optional>true</optional> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency>  <dependency> <groupId>com.baomidou</groupId> <artifactId>mybatis-plus-boot-starter</artifactId> <version>3.4.0</version> </dependency>
这下面就是我xml文件里面怎么写的嵌套查询语句
<mapper namespace="com.itheima.mybatisplus.mapper.UserMapper">  <resultMap id="authority" type="com.itheima.mybatisplus.domain.User"> <id column="id" property="id"/> <id column="password" property="password"/> <id column="age" property="age"/> <id column="email" property="email"/> <id column="name" property="name"/> <id column="user_name" property="username"/> <collection property="list" ofType="com.itheima.mybatisplus.domain.Authority"> <id property="id" column="aid"/> <id property="name" column="aname"/> </collection> <select id="selectAuthorityById" parameterType="int" resultMap="authority"> SELECT * FROM authority a,tb_user t,user_authority ua WHERE a.aid=ua.authority_id AND t.id=ua.user_id AND t.id=#{id} </select>
数据库的配置我就不放了，直接编写就可以了，看会下面这个xml配置就可以了

一对多查询(经典案例)

条件
查询班级表返回所有学生信息（一对多问题）

数据库
Java技术迷

班级class_info

学生student

代码实现
<!- - <collection property=""- ->
实体类ClassInfo.java
`@Data
public class ClassInfo {

private Long id;
private String name;
private String nameTest; 
private List<Student> studentList;

}ClassInfoMapper.xml<?xml version=”1.0” encoding=”UTF-8”?>
<!DOCTYPE mapper PUBLIC “-//mybatis.org//DTD Mapper 3.0//EN” “">http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<!--    查询班级 返回所有学生的信息   一对多-->
<!--    自定义映射规则-->
<resultMap id="OneToMany" type="com.qcby.zsgc.entity.ClassInfo">
    <result column="name" jdbcType="VARCHAR" property="nameTest" />
    <collection  column="{id1=id,name=name}"
                 property="studentList"
                 select="com.example.demo.mapper.StudentMapper.listByClassInfoId">                 </collection>
</resultMap>
<select id="listAllWithStudent" resultMap="OneToMany">
    select * from class_info

关联StudentMapper.xml中的子查询
<select id="listByClassInfoId" resultType="com.example.demo.entity.Student"> SELECT * FROM student s where class_info_id = #{id1} or name = #{name} </select>
ClassInfoMapper.java
public interface ClassInfoMapper extends BaseMapper<ClassInfo> { IPage<ClassInfo> listAllWithStudent(IPage<ClassInfo> page); }
ClassInfoService.java
public interface ClassInfoService extends IService<ClassInfo> { IPage<ClassInfo> listAllWithStudent(IPage<ClassInfo> page); }
ClassInfoServiceImpl.java
@Servicepublic class ClassInfoServiceImpl extends ServiceImpl<ClassInfoMapper, ClassInfo> implements ClassInfoService { @Autowired private StudentService studentService; @Override public IPage<ClassInfo> listAllWithStudent(IPage<ClassInfo> page) { return this.baseMapper.listAllWithStudent(page); }}
ClassInfoController.java
`@Controller
@RequestMapping(“classInfo”)
public class ClassInfoController {

@Autowired
private ClassInfoService classInfoService;
@RequestMapping("listAllWithStudent")
@ResponseBody
public IPage<ClassInfo> listAllWithStudent(Integer pageNo,Integer pageSize){
    Page<ClassInfo> page = new Page<>(pageNo,pageSize);
    return classInfoService.listAllWithStudent(page);
}

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