Mybatis

CRUD(数据和配置使用Mybatis快速入门)

select标签

选择，查询语句:

<select id="getUserById" resultType="com.louis.pojo.User" parameterType="int"></select>

id:就是对应namespace中的方法名(就相当于重写了原来的方法)
resultType：sql语句执行的返回值
parameterType:表示参数类型，和传入的参数有关
namesepace中的包名要和Dao/mapper接口的包名一致。

UserDao接口

//根据id查询用户
User getUserById(Integer id);

UserMapper.xml

<select id="getUserById" resultType="com.louis.pojo.User" parameterType="int">
    select * from mybatis.user where id = #{id};
</select>

测试类

@Test
public void testUserById(){
    SqlSession sqlSession = MybatisUtils.getsqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    System.out.println(mapper.getUserById(1));
    sqlSession.close();
}

insert标签

UserDao接口

//insert一个用户
int addUser(User user);

UserMapper.xml

<!--对象中的属性可以直接取到-->
<insert id="addUser" parameterType="com.louis.pojo.User" >
    insert into mybatis.user (id, name, pwd) values (#{id}, #{name}, #{pwd});
</insert>

测试类

@Test
public void addUser(){
    SqlSession sqlSession = MybatisUtils.getsqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    mapper.addUser(new User(4, "DC", "12wa"));
    sqlSession.close();
}

通过上述方法我们可以执行成功，但在数据库中并没有插入相关的数据，这是事务导致。

解决方法

@Test
public void addUser(){
    SqlSession sqlSession = MybatisUtils.getsqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    int dc = mapper.addUser(new User(4, "DC", "12wa"));
    //解决数据库中未插入的情况，增删改需要提交事务
    if(dc > 0){
        System.out.println("插入成功");
        //提交
        sqlSession.commit();
    }
    sqlSession.close();
}

update标签

UserDao接口

//修改用户
int updateUser(User user);

UserMapper.xml

<update id="updateUser" parameterType="com.louis.pojo.User">
    update mybatis.user set name = #{name}, pwd = #{pwd} where id = #{id};
</update>

测试类

@Test
public void updateUser(){
    SqlSession sqlSession = MybatisUtils.getsqlSession();
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    int i = userMapper.updateUser(new User(3, "微微", "Lzh"));
    if(i > 0){
        sqlSession.commit();
    }
    sqlSession.close();
}

delete标签

UserDao接口

//删除用户
int deleteUser(int id);

UserMapper.xml

<delete id="deleteUser" parameterType="int">
    delete from mybatis.user where id = #{id};
</delete>

测试

@Test
public void deleteUser(){
    SqlSession sqlSession = MybatisUtils.getsqlSession();
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    int result = userMapper.deleteUser(4);
    if(result > 0){
        sqlSession.commit();
    }
    sqlSession.close();
}

增删改在没有设置自动提交的时候需要手动提交事务。

Map

假设我们的实体类或者数据库中的表字段或者参数过多，我们应当考虑使用map。
Map传递参数:直接在sql中取出key即可(parameterType=“map”)
对象传递参数:直接在sql中取对象的属性即可(parameterType=“com.louis.pojo.User”)
只有一个基本类型参数的情况下，可以直接在sql中取到。多个参数用Map，或者注解。

Map示例

UserDao接口

//Map
int addUser2(Map<String, Object> map);

UserMapper.xml

<insert id="addUser2" parameterType="map">
    insert into mybatis.user (id, name, pwd) values (#{userId}, #{userName}, #{password});
</insert>

测试类

@Test
public void addUser2(){
    SqlSession sqlSession = MybatisUtils.getsqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    Map<String, Object> map = new HashMap<>();
    map.put("userId", 5);
    map.put("userName", "咕噜咕噜");
    map.put("password", "xzz");
    int result = mapper.addUser2(map);
    if(result > 0){
        sqlSession.commit();
    }
    sqlSession.close();
}

模糊查询

UserDao接口

//模糊查询
List<User> selectUserLike(String value);

UserMapper.xml

<select id="selectUserLike">
    select * from mybatis.user where name like #{value};
</select>

测试类

@Test
public void selectUserLike(){
    SqlSession sqlSession = MybatisUtils.getsqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    List<User> users = mapper.selectUserLike("%微%");
    for (User user : users) {
        System.out.println(user);
    }
    sqlSession.close();
}

上面使用的方法存在sql注入的情况，优化如下：

UserMapper.xml

<select id="selectUserLike">
    select * from mybatis.user where name like "%" #{value}"%";
</select>

测试类

@Test
public void selectUserLike(){
    SqlSession sqlSession = MybatisUtils.getsqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    List<User> users = mapper.selectUserLike("微");
    for (User user : users) {
        System.out.println(user);
    }
    sqlSession.close();
}