Mybatis动态拼接sql
需求：查询某张表时条件不确定，可能有一个，可能有多个，也可能没有条件

<!-- 动态sql -->
<select id="fingUserList" parameterType="com.hl.myabtis.first.beas.UserQueryVo" resultType="com.hl.myabtis.first.beas.UserCustomer">
        select * from user
<!-- where可以自动去掉条件中的第一个and -->
<where>
    <if test="userCustomer!=null">
        <if test="userCustomer.sex!=null and userCustomer.sex!=''">
        and user.sex=#{userCustomer.sex}
        </if>
        <if test="userCustomer.address!=null and userCustomer.address!=''">
        and user.address like '$%{userCustomer.address}%'
        </if>
    </if>
</where>

mapper接口：

public List<UserCustomer> fingUserList(UserQueryVo userQueryVo) throws Exception;

测试：

@Test
    public void findUserCount() throws Exception{
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper usermapper = sqlSession.getMapper(UserMapper.class);
        //构建一个包装类
        UserQueryVo userQueryVo = new UserQueryVo();
        //构建一个增强类
        UserCustomer userCustomer = new UserCustomer();
        userCustomer.setAddress("明月");
        userCustomer.setSex('1');
        //包装类包装这增强类作为查询条件
        userQueryVo.setUserCustomer(userCustomer);
        //不加任何条件
        int result = usermapper.findUserCount(null);
        System.out.println(result);
        sqlSession.close();
    }