Mybatis学习笔记7 - select查询的相关属性使用-优快云博客

本文详细介绍了在MyBatis框架中如何处理返回类型为集合List和Map的情况，包括正确的resultType设置、@MapKey注解的使用，以及通过示例代码展示了具体的实现方式。

1、当接口的返回类型是集合List时，resultType要写集合中元素的类型

示例如下：

接口定义：
package com.mybatis.dao;

import com.mybatis.bean.Employee;

import java.util.*;

public interface EmployeeMapper {
    public List<Employee> getEmpByLastName(String lastName);
}

mapper定义：
<?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">
<mapper namespace="com.mybatis.dao.EmployeeMapper">
    <select id="getEmpByLastName" resultType="com.mybatis.bean.Employee">
        select * from tbl_employee where last_name like #{lastName}
    </select>
</mapper>

测试代码：
package com.mybatis.demo;

import java.io.*;
import java.util.*;

import com.mybatis.bean.Employee;
import com.mybatis.dao.EmployeeMapper;
import org.apache.ibatis.io.*;
import org.apache.ibatis.session.*;
import org.junit.Test;

public class MyTest {
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void testSelect() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession(true);
        try {
            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
            List<Employee> employees = mapper.getEmpByLastName("%e%");
            for (Employee emp : employees) {
                System.out.println(emp);
            }
        } finally {
            openSession.close();
        }
    }
}

2、@MapKey注解：指定使用哪个实体的属性作为key

示例如下：

接口定义：
package com.mybatis.dao;

import com.mybatis.bean.Employee;
import org.apache.ibatis.annotations.MapKey;

import java.util.*;

public interface EmployeeMapper {
    //返回一条记录的map；key就是列名，值就是对应的值
    public Map<String, Object> getEmpByIdReturnMap(Integer id);

    //多条记录封装一个map：Map<Integer,Employee>:键是这条记录的主键，值是记录封装后的javaBean
    //@MapKey:告诉mybatis封装这个map的时候使用哪个属性作为map的key
    @MapKey("id")
    public Map<Integer, Employee> getEmpReturnMap(String lastName);
}

mapper定义：
<?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">
<mapper namespace="com.mybatis.dao.EmployeeMapper">
    <!--public Map<String, Object> getEmpByIdReturnMap(Integer id);-->
    <select id="getEmpByIdReturnMap" resultType="map">
 		select * from tbl_employee where id=#{id}
 	</select>

    <!--public Map<Integer, Employee> getEmpReturnMap(String lastName);  -->
    <select id="getEmpReturnMap" resultType="com.mybatis.bean.Employee">
 		select * from tbl_employee where last_name like #{lastName}
 	</select>
</mapper>

测试代码：
package com.mybatis.demo;

import java.io.*;
import java.util.*;

import com.mybatis.bean.Employee;
import com.mybatis.dao.EmployeeMapper;
import org.apache.ibatis.io.*;
import org.apache.ibatis.session.*;
import org.junit.Test;

public class MyTest {
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void testSelectOne() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession(true);
        try {
            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
            Map<String, Object> employee = mapper.getEmpByIdReturnMap(1);
            System.out.println(employee);
        } finally {
            openSession.close();
        }
    }

    @Test
    public void testSelectMany() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession(true);
        try {
            EmployeeMapper mapper = openSession.getMapper(EmployeeMapper.class);
            Map<Integer, Employee> employee = mapper.getEmpReturnMap("%e%");
            System.out.println(employee);
        } finally {
            openSession.close();
        }
    }
}

转载于:https://www.cnblogs.com/xidian2014/p/10350041.html