目录
1.查询一个实体类对象
<select id="getUserById" resultType="User">
select * from t_user where id=#{id};
</select> @Test
public void test() {
SqlSessionUtils sqlSessionUtils = new SqlSessionUtils();
SqlSession sqlSession = sqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
User user = mapper.getUserById(2);
System.out.println(user);
}表：
查询结果：
假如，我把后面的条件删除，会发生什么情况呢？
2.查询一个list集合
<select id="getAllUser" resultType="User">
select * from t_user;
</select>测试类：
@Test
public void test2(){
SqlSessionUtils sqlSessionUtils = new SqlSessionUtils();
SqlSession sqlSession = sqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
List<User> allUser = mapper.getAllUser();
allUser.forEach(System.out::println);
}查询结果：
3.查询单个数据
<select id="getCount" resultType="java.lang.Integer">
select count(id) from t_user;
</select>测试类：
@Test
public void test3(){
SqlSessionUtils sqlSessionUtils = new SqlSessionUtils();
SqlSession sqlSession = sqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
Integer count = mapper.getCount();
System.out.println(count);
}
表：
查询结果：
4.查询一条数据为map集合
<!--Map<String, Object> getUserToMap(@Param("id") int id);-->
<select id="getUserToMap" resultType="map">
select * from t_user where id = #{id}
</select>测试类：
@Test
public void test4(){
SqlSessionUtils sqlSessionUtils = new SqlSessionUtils();
SqlSession sqlSession = sqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
Map<String, Object> map = mapper.getUserToMap(4);
System.out.println(map);
}
5.查询多条数据为map集合
①方式一
<!--Map<String, Object> getAllUserToMap();-->
<select id="getAllUserToMap" resultType="map">
select * from t_user
</select>测试类：
@Test
public void test5(){
SqlSessionUtils sqlSessionUtils = new SqlSessionUtils();
SqlSession sqlSession = sqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
List<Map<String, Object>> allUserToMap = mapper.getAllUserToMap();
System.out.println(allUserToMap);
}
②方式二
<select id="getAllUserToMap" resultType="map">
select * from t_user
</select>测试类：
@Test
public void test6(){
SqlSessionUtils sqlSessionUtils = new SqlSessionUtils();
SqlSession sqlSession = sqlSessionUtils.getSqlSession();
SelectMapper mapper = sqlSession.getMapper(SelectMapper.class);
Map<String, Object> allUserToMap = mapper.getAllUserToMap();
System.out.println(allUserToMap);
}
运行结果：
