Mybatis代理开发、动态sql、核心配置文件

咕咕星

发布于 2021-01-05 09:49:28

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发布于 2021-01-05 09:49:28

文章被收录于专栏：咕咕星

1、Mybatis代理开发

只需要编写Mapper 接口，Mybatis 框架根据接口定义创建接口的动态代理对象

Mapper 接口开发需要遵循以下规范：

Mapper.xml文件中的namespace与mapper接口的全限定名相同

2、MyBatis动态sql

在Mapper.xml文件中可以使用：<where>、<if>、<foreach>等标签

例子一：

<select id="findUserByCondition" resultType="user" parameterType="user">
    select * from user
    <where>
        <if test="id!=0">
            and id = #{id}
        </if>
        <if test="username!=null">
            and username = #{username}
        </if>
    </where>
</select>

@Test
//MyBatis动态sql
public void test6() throws IOException {
    InputStream resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
    SqlSession sqlSession = sqlSessionFactory.openSession();

    //测试数据
    User condition  = new User();
    condition.setUsername("lisi");

    //获得MyBatis框架生成的UserMapper接口的实现类
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    User userByCondition = userMapper.findUserByCondition(condition );
    System.out.println(userByCondition);

    sqlSession.close();

}

例子二：

<select id="findUserByIds" resultType="user" parameterType="list">
    select * from user
    <where>
        <foreach collection="list" item="id" open="id in (" close=")" separator=",">
            #{id}
        </foreach>
    </where>
</select>

@Test
//MyBatis动态sql
public void test7() throws IOException {
    InputStream resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
    SqlSession sqlSession = sqlSessionFactory.openSession();

    //测试数据
    List arrayList = new ArrayList();
    arrayList.add(1);
    arrayList.add(2);

    //获得MyBatis框架生成的UserMapper接口的实现类
    UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
    List<User> userList = userMapper.findUserByIds(arrayList);
    System.out.println(userList);

    sqlSession.close();

}

foreach标签的属性：

collection：代表要遍历的集合元素，注意编写时不要写#{}
open：代表语句的开始部分
close：代表结束部分
item：代表遍历集合的每个元素，生成的变量名
sperator：代表分隔符

3、SQL片段抽取

<!--将重复的sql提取出来-->
<sql id="selectAll">select * from user</sql>

<select id="findUserByIds" resultType="user" parameterType="list">
    <!--用include引用-->
    <include refid="selectAll"></include>
    <where>
        <foreach collection="list" item="id" open="id in (" close=")" separator=",">
            #{id}
        </foreach>
    </where>
</select>