day111 - mybatis中的参数问题

mybatis中的参数问题

样例：根据用户名查询用户信息

mybatis中获取参数值的方式有两种#{}和${}

1. 若mapper接口方法的参数为单个的字面量类型

User getUserByUsername(String username);

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

@Test
public void testGetUserByUsername(){
    SqlSession sqlSession = SqlSessionUtil.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    User user = mapper.getUserByUsername("admin");
    System.out.println(user);
}

此时用#{}和${}任意内容获取参数值，注意${}的单引号问题

#{}的本质是占位符 ${}的本质是sql语句拼接

2.若mapper接口方法的参数为多个的字面量类型

/**
 * 验证登录
 * @param username
 * @param password
 * @return
 */
User checkLogin(String username, String password);

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

@Test
public void testCheckLogin(){
    SqlSession sqlSession = SqlSessionUtil.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    User user = mapper.checkLogin("admin","123456");
    System.out.println(user);
}

此时mabatis会将参数放在map集合中，一两种方式进行存储

a> arg0，arg1....
b> param1,param2...

需要通过#{}和${}获取mapper中的值

3.若mapper接口的参数为map集合时

/**
 * 验证登录 以map集合作为参数方式
 * @param map
 * @return
 */
User checkLoginByMap(Map<String, Object> map);

<!--User checkLoginByMap(Map<String, Object> map);-->
<select id="checkLoginByMap" resultType="com.gu.mybatis.pojo.User">
    select * from t_user where username =#{username} and password =#{password}
</select>

@Test
public void testCheckLoginByMap(){
    SqlSession sqlSession = SqlSessionUtil.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    Map< String, Object> map = new HashMap<>();
    map.put("username", "admin");
    map.put("password","123456");
    User user = mapper.checkLoginByMap(map);
    System.out.println(user);
}

需要通过#{}和${}获取mapper中的值

键值要与map集合中的键值一致

4. 若mapper接口方法的参数为实体类类型的参数

/**
 * 添加用户
 * @param user
 */
void insertUser(User user);

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

@Test
public void testInsertUser(){
    SqlSession sqlSession = SqlSessionUtil.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    User user = new User(null,"root","123456",33,"女","hahahaha");
    mapper.insertUser(user);
}

只需要通过#{}和${}访问实体类中的属性名，可以获取相应的属性值

5. 在mapper接口的参数上设置@Param注解

/**
 * 验证登录，使用param注解
 * @param username
 * @param password
 * @return
 */
User checkLoginByParam(@Param("username") String  username,@Param("password") String password);

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

@Test
public void testCheckLoginByParam(){
    SqlSession sqlSession = SqlSessionUtil.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    User user = mapper.checkLoginByParam("admin","123456");
    System.out.println(user);
}

mybatis会将这些参数放在map中，以两种方式存储
* a>以注解的value属性为键，以参数为值
* b>以param1，param2为键，以参数值只需要通过#{}和${}访问map的属性名，可以获取相应的属性值