mybatis——返回结果类型为集合类型（List、Map）

本章节主要讲解如果Mapper接口的返回类型为集合（List、Map）时，如何定义

一、返回结果类型为List

Mapper接口的方法：

 List<Employee> getAll();

EmployeeMapper.xml映射文件：

<select id="getAll" resultType="com.wcg.mybatis.entity.Employee">
    select id,last_name ,email,gender from tbl_employee
</select>

在resultType定义返回结果List中的元素类型即可：

List<Employee> --> resultType="com.wcg.mybatis.entity.Employee"

测试方法：

@Test
public void selectAllTest(){
    // 获取 SqlSession 的实例 。SqlSession 完全包含了面向数据库执行 SQL 命令所需的所有方法。通过 SqlSession 实例来直接执行已映射的 SQL 语句
    SqlSession sqlSession = null;
    try {
        sqlSession = sessionFactory.openSession();
        // 通过获取接口代理对象来执行sql语句
        EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
        List<Employee> employeeList = mapper.getAll();
        for (Employee employee : employeeList) {
            System.out.println("name: "+ employee.getLastName());
        }
    } finally {
        // 资源关闭，放在finally中确保一定会执行
        sqlSession.close();
    }
}

结果：

DEBUG 05-07 23:46:31,854 ==>  Preparing: select id,last_name ,email,gender from tbl_employee   (BaseJdbcLogger.java:145) 
DEBUG 05-07 23:46:31,905 ==> Parameters:   (BaseJdbcLogger.java:145) 
DEBUG 05-07 23:46:31,927 <==      Total: 3  (BaseJdbcLogger.java:145) 
name: BB
name: CC
name: DD

二、返回结果类型为Map

返回一行数据：

Mapper接口的方法：

Map<String, Object> getEmpById(@Param("id") Integer id);

EmployeeMapper.xml映射文件：

<select id="getEmpById" resultType="map">
    select id,last_name ,email,gender from tbl_employee where id = #{id}
</select>

则Map<String, Object>中，String对应着字段名，Object对应着字段值

测试方法：

@Test
public void selectMapTest(){
    // 获取 SqlSession 的实例 。SqlSession 完全包含了面向数据库执行 SQL 命令所需的所有方法。通过 SqlSession 实例来直接执行已映射的 SQL 语句
    SqlSession sqlSession = null;
    try {
        sqlSession = sessionFactory.openSession();
        // 通过获取接口代理对象来执行sql语句
        EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
        Map<String, Object> empMap = mapper.getEmpById(2);
        Set<Map.Entry<String, Object>> entries = empMap.entrySet();
        Iterator<Map.Entry<String, Object>> iterator = entries.iterator();
        while (iterator.hasNext()){
            Map.Entry<String, Object> next = iterator.next();
            System.out.println(next.getKey()+" : "+next.getValue());
        }
    } finally {
        // 资源关闭，放在finally中确保一定会执行
        sqlSession.close();
    }
}

结果：

DEBUG 05-07 23:45:03,837 ==>  Preparing: select id,last_name ,email,gender from tbl_employee where id = ?   (BaseJdbcLogger.java:145) 
DEBUG 05-07 23:45:03,882 ==> Parameters: 2(Integer)  (BaseJdbcLogger.java:145) 
DEBUG 05-07 23:45:03,937 <==      Total: 1  (BaseJdbcLogger.java:145) 
gender : 0
last_name : BB
id : 2
email : [email protected]

返回多行数据：

Mapper接口的方法：

@MapKey("id")
Map<Integer, Employee> getAllEmp();

EmployeeMapper.xml映射文件：

<select id="getAllEmp" resultType="employee">
    select id,last_name ,email,gender from tbl_employee
</select>

通过@MapKey定义返回Map集合的key是哪个字段的值，Map集合的Value则为每行数据的值

 

测试方法：

@Test
public void selectMapKeyTest(){
    // 获取 SqlSession 的实例 。SqlSession 完全包含了面向数据库执行 SQL 命令所需的所有方法。通过 SqlSession 实例来直接执行已映射的 SQL 语句
    SqlSession sqlSession = null;
    try {
        sqlSession = sessionFactory.openSession();
        // 通过获取接口代理对象来执行sql语句
        EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
        Map<Integer, Employee> empMap = mapper.getAllEmp();
        Set<Map.Entry<Integer, Employee>> entries = empMap.entrySet();
        Iterator<Map.Entry<Integer, Employee>> iterator = entries.iterator();
        while (iterator.hasNext()){
            Map.Entry<Integer, Employee> next = iterator.next();
            System.out.println(next.getKey()+" : "+next.getValue().getLastName());
        }
    } finally {
        // 资源关闭，放在finally中确保一定会执行
        sqlSession.close();
    }
}

结果：

DEBUG 05-07 23:30:54,624 ==>  Preparing: select id,last_name ,email,gender from tbl_employee   (BaseJdbcLogger.java:145) 
DEBUG 05-07 23:30:54,712 ==> Parameters:   (BaseJdbcLogger.java:145) 
DEBUG 05-07 23:30:54,738 <==      Total: 3  (BaseJdbcLogger.java:145) 
2 : BB
4 : CC
5 : DD