MyBatis获取参数值方式

MyBatis获取参数值的两种方式：${}与#{}

${}的本质就是字符串拼接，#{}的本质就是占位符赋值 

${}使用字符串拼接的方式拼接sql，若为字符串类型或日期类型的字段进行赋值时，需要手动加单引号；
但是#{}使用占位符赋值的方式拼接sql，此时为字符串类型或日期类型的字段进行赋值时，可以自动添加单引号

情况一：mapper接口方法参数为单个字面量类型

@Test
public void testMybatis() throws IOException {
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    ParameterMapper parameterMapper = sqlSession.getMapper(ParameterMapper.class);
    List<User> result = parameterMapper.getUserByUsername("张三");
    result.forEach(user -> System.out.println(user));
}

<!--User getUserByUsername(String username);-->
<select id="getUserByUsername" resultType="User">
select * from t_user where username = #{username}
</select>

情况二：mapper接口方法参数为多个

• 使用arg0，arg1，…… 或 param1，param2，…… 为键，参数为值
• 只需通过#{}或${}以键的方式访问值即可

@Test
public void testMybatis() throws IOException {
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    ParameterMapper parameterMapper = sqlSession.getMapper(ParameterMapper.class);
    List<User> result = parameterMapper.checkLogin("张三", "123456");
    result.forEach(user -> System.out.println(user));
}

<!--User checkLogin(String username, String password)-->
<select id="checkLogin" resultType="User">
    select * from t_user where username = #{arg0} and password = #{arg1}
</select>

情况三：mapper接口方法参数有多个，可以手动放在一个map中存储

• 只需通过#{}或${}以键的方式访问值即可

@Test
public void testMybatis() throws IOException {
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    ParameterMapper parameterMapper = sqlSession.getMapper(ParameterMapper.class);
    Map<String, Object> mp = new HashMap<>();
    mp.put("username", "张三");
    mp.put("password", "123456");
    List<User> result = parameterMapper.checkLoginByMap(mp);
    result.forEach(user -> System.out.println(user));
}

<!--List<User> checkLoginByMap(Map<String, Object> mp)-->
<select id="checkLoginByMap" resultType="User">
    select * from t_user where username = #{username} and password = #{password}
</select>

情况四：参数是一个实体类类型

• 直接通过属性名访问属性值

@Test
public void testMybatis() throws IOException {
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    ParameterMapper parameterMapper = sqlSession.getMapper(ParameterMapper.class);
    User user = new User("Alice", "666666", 22, "女", "666@163.com");
    int result = parameterMapper.insertUser(user);
    System.out.println(result);
}

<!--int insertUser(User user)-->
<insert id="insertUser">
    insert into t_user values(null, #{username}, #{password}, #{age}, #{sex}, #{email})
</insert>

情况五：通过@param命名参数

• 以@param注解的值 或 param1，param2，……为键，以参数为值

@Test
public void testMybatis() throws IOException {
    SqlSession sqlSession = SqlSessionUtils.getSqlSession();
    ParameterMapper parameterMapper = sqlSession.getMapper(ParameterMapper.class);
    List<User> result = parameterMapper.checkLoginByParam("Alice", "666666");
    result.forEach(User -> System.out.println(User));
}

<!--List<User> checkLoginByParam(@Param("username") String username, @Param("password") String password)-->
<select id="checkLoginByParam" resultType="User">
    select * from t_user where username = #{username} and password = #{password}
</select>

建议整合为两种情况

• 参数是实体类对象
• 否则全都用@param