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。
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@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
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@Data@TableNamepublic class Authority { @TableId(type = IdType.INPUT) @TableField("aid") private int id; @TableId("aname") private String name;} |
测试类
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@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
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<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> <!--mybatis plus 起步依赖--> <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
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<mapper namespace="com.itheima.mybatisplus.mapper.UserMapper"> <!--返回的对象为authority--> <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
班级class_info
学生student
代码实现
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<!-- 多对一 或者 一对一 --><!-- <association property=""--><!-- 一对多 返回集合--><!- - <collection property=""- -> |
实体类ClassInfo.java
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@Datapublic class ClassInfo { private Long id; private String name; private String nameTest; private List<Student> studentList;} |
ClassInfoMapper.xml
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<?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"><!--名称空间：对应mapper层某个接口的包的全名称--><mapper namespace="com.example.demo.mapper.ClassInfoMapper"> <!-- 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 </select> |
关联StudentMapper.xml中的子查询
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<select id="listByClassInfoId" resultType="com.example.demo.entity.Student"> SELECT * FROM student s where class_info_id = #{id1} or name = #{name} </select> |
ClassInfoMapper.java
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public interface ClassInfoMapper extends BaseMapper<ClassInfo> { IPage<ClassInfo> listAllWithStudent(IPage<ClassInfo> page); } |
ClassInfoService.java
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public interface ClassInfoService extends IService<ClassInfo> { IPage<ClassInfo> listAllWithStudent(IPage<ClassInfo> page); } |
ClassInfoServiceImpl.java
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@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
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@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); } } |
以上为个人经验，希望能给大家一个参考，也希望大家多多支持服务器之家。
原文链接：https://blog.csdn.net/weixin_52366309/article/details/114293133
