当前位置:Gxlcms > 数据库问题 > Mybatis动态sql

Mybatis动态sql

时间:2021-07-01 10:21:17 帮助过:8人阅读

List<User> users = userMapper.queryUserByWhere(user); for (User u: users) { System.out.println(u); } // 和spring整合后由spring管理 sqlSession.close(); }

执行测试方法,查看控制台日志:

DEBUG [main] - ==>  Preparing: SELECT id, username, birthday, sex, address FROM `user` WHERE sex = ? AND username LIKE ‘%张%‘ 
DEBUG [main] - ==> Parameters: 1(String)
DEBUG [main] - <==      Total: 4
User [id=10, username=张三, sex=1, birthday=Thu Jul 10 00:00:00 CST 2014, address=北京市]
User [id=16, username=张小明, sex=1, birthday=null, address=河南郑州]
User [id=24, username=张三丰, sex=1, birthday=null, address=河南郑州]
User [id=27, username=张飞, sex=1, birthday=Mon Dec 25 00:00:00 CST 2017, address=蜀国]

假设现在不需要性别这个条件了,注释掉 user.setSex("1"),测试结果如下:

DEBUG [main] - ==>  Preparing: SELECT id, username, birthday, sex, address FROM `user` WHERE sex = ? AND username LIKE ‘%张%‘ 
DEBUG [main] - ==> Parameters: null
DEBUG [main] - <==      Total: 0

这显然不合理。

按照之前所学的,要解决这个问题,需要编写多个sql,查询条件越多,需要编写的sql就更多了,显然这样是不靠谱的。

解决方案,使用动态sql的if标签。

 

(4)使用if标签

    <!-- 根据条件查询用户 -->
    <select id="queryUserByWhere" parameterType="user" resultType="user">
        SELECT id, username, birthday, sex, address FROM `user`
        WHERE 1=1
        <if test="sex != null and sex !=‘‘">
            AND sex = #{sex}
        </if>
        <if test="username != null and username != ‘‘">
            AND username LIKE ‘%${username}%‘
        </if>
    </select>

注意字符串类型的数据需要要做不等于空字符串校验。另外,为什么where后加上 1=1,因为如果不加这个,当代码中注释掉 user.setSex("1") 时,打印出来的sql语句就是 “where      and username like...”,显然语法错误。

还是注释掉 user.setSex("1"),再次执行测试方法,查看控制台日志:

DEBUG [main] - ==>  Preparing: SELECT id, username, birthday, sex, address FROM `user` WHERE 1=1 AND username LIKE ‘%张%‘ 
DEBUG [main] - ==> Parameters: 
DEBUG [main] - <==      Total: 4
User [id=10, username=张三, sex=1, birthday=Thu Jul 10 00:00:00 CST 2014, address=北京市]
User [id=16, username=张小明, sex=1, birthday=null, address=河南郑州]
User [id=24, username=张三丰, sex=1, birthday=null, address=河南郑州]
User [id=27, username=张飞, sex=1, birthday=Mon Dec 25 00:00:00 CST 2017, address=蜀国]

 

2. where标签

上面的sql还有where 1=1 这样的语句,很麻烦。可以使用where标签进行改造。

    <!-- 根据条件查询用户 -->
    <select id="queryUserByWhere" parameterType="user" resultType="user">
        SELECT id, username, birthday, sex, address FROM `user`
        <where>
            <if test="sex != null and sex !=‘‘">
                AND sex = #{sex}
            </if>
            <if test="username != null and username != ‘‘">
                AND username LIKE ‘%${username}%‘
            </if>
        </where>
    </select>

 

3. sql片段

Sql中可将重复的sql提取出来,使用时用include引用即可,最终达到sql重用的目的。

把上面例子中的id, username, birthday, sex, address提取出来,作为sql片段,如下:

    <!-- sql片段 -->
    <select id="queryUserBySql" parameterType="user" resultType="user">
        <!-- SELECT id, username, birthday, sex, address FROM `user` -->
        <!-- 使用include标签加载sql片段;refid是sql片段id -->
        SELECT <include refid="userFields" /> FROM `user`
        <!-- where标签可以自动添加where关键字,同时处理sql语句中第一个and关键字 -->
        <where>
            <if test="sex != null">
                AND sex = #{sex}
            </if>
            <if test="username != null and username != ‘‘">
                AND username LIKE
                ‘%${username}%‘
            </if>
        </where>
    </select>

    <!-- 声明sql片段 -->
    <sql id="userFields">
        id, username, birthday, sex, address
    </sql>

 

4. foreach标签

向sql传递数组或List,mybatis使用foreach解析,如下:

根据多个id查询用户信息,查询sql:

SELECT * FROM user WHERE id IN (1,10,24)

(1)UserMapper.java添加方法(存在三种形式)

    //根据多个id查询用户信息
    public List<User> queryUserByIds(Integer[] ids);
    public List<User> queryUserByIds(List<Integer> ids);
    public List<User> queryUserByIds(QueryVo vo);

 

先来个 public List<User> queryUserByIds(QueryVo vo); 改造QueryVo.java

如下图在pojo中定义list属性ids存储多个用户id,并添加getter/setter方法。

public class QueryVo implements Serializable { //序列化,对象转成二进制进行传输。

	private static final long serialVersionUID = 1L;

	private User user;
	
	List<Integer> idsList;
	
	Integer[] ids;
	
	public List<Integer> getIdsList() {
		return idsList;
	}
	public void setIdsList(List<Integer> idsList) {
		this.idsList = idsList;
	}
	public Integer[] getIds() {
		return ids;
	}
	public void setIds(Integer[] ids) {
		this.ids = ids;
	}
	public User getUser() {
		return user;
	}
	public void setUser(User user) {
		this.user = user;
	}

}

 

(2)Mapper.xml文件

UserMapper.xml添加sql,如下:

    <!--根据多个id查询用户信息 (1,2,3)-->
    <select id="queryUserByIds" parameterType="QueryVo" resultType="user">
        SELECT * FROM `user`
        <where>
            id IN
            <!-- foreach标签,进行遍历 -->
            <!-- collection:遍历的集合,这里是QueryVo的ids属性 -->
            <!-- item:遍历的项目,可以随便写,,但是和后面的#{}里面要一致 -->
            <!-- open:在前面添加的sql片段 -->
            <!-- close:在结尾处添加的sql片段 -->
            <!-- separator:指定遍历的元素之间使用的分隔符 -->
            <foreach collection="idsList" item="item" separator="," open="(" close=")">
                #{item}
            </foreach>
        </where>
    </select>

或者将 id IN 放进 open 中,如下:

<foreach collection="idslist" item="item" separator="," open="id IN (" close=")">

 

(4)测试方法

    //根据多个ID查询用户
    @Test
    public void testID() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);

        // 获取sqlSession,和spring整合后由spring管理
        SqlSession sqlSession = sqlSessionFactory.openSession();

        //SqlSEssion会帮我生成一个实现类  (需要我们给接口,它帮我们生成实现类,返回给我们的还是接口)
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        QueryVo vo = new QueryVo();
        List<Integer> ids = new ArrayList<>();
        ids.add(10);
        ids.add(16);
        ids.add(22);
        vo.setIdsList(ids);

        List<User> users = userMapper.queryUserByIds(vo);
        for (User u: users) {
            System.out.println(u);
        }

        // 和spring整合后由spring管理
        sqlSession.close();

    }

执行测试方法,查看控制台日志:

DEBUG [main] - ==>  Preparing: SELECT * FROM `user` WHERE id IN ( ? , ? , ? ) 
DEBUG [main] - ==> Parameters: 10(Integer), 16(Integer), 22(Integer)
DEBUG [main] - <==      Total: 3
User [id=10, username=张三, sex=1, birthday=Thu Jul 10 00:00:00 CST 2014, address=北京市]
User [id=16, username=张小明, sex=1, birthday=null, address=河南郑州]
User [id=22, username=陈小明, sex=1, birthday=null, address=河南郑州]

 

在实现一个 public List<User> queryUserByIds(Integer[] ids);

修改UserMapper.xml,如下:

    <!--根据多个id查询用户信息 (1,2,3)-->
    <select id="queryUserByIds" parameterType="QueryVo" resultType="user">
        SELECT * FROM `user`
        <where>
            id IN
            <foreach collection="array" item="item" separator="," open="(" close=")">
                #{item}
            </foreach>
        </where>
    </select>

【注意】:当传递的参数是数组时,collection的值一定要是array,否则会报错。同样地,当传递的参数是list的时候,collection的值一定要是list。而当传入的参数是个对象(比如QueryVo)时,直接使用对象里面的属性名(比如上例中是idsList)。

测试方法:

    //根据多个ID查询用户
    @Test
    public void testID2() throws Exception {
        //加载核心配置文件
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        //创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);

        // 获取sqlSession,和spring整合后由spring管理
        SqlSession sqlSession = sqlSessionFactory.openSession();

        //SqlSEssion会帮我生成一个实现类  (需要我们给接口,它帮我们生成实现类,返回给我们的还是接口)
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

        Integer[] ids = new Integer[3];
        ids[0] = 16;
        ids[1] = 22;
        ids[2] = 10;

        List<User> users = userMapper.queryUserByIds(ids);
        for (User u: users) {
            System.out.println(u);
        }

        // 和spring整合后由spring管理
        sqlSession.close();

    }

执行测试方法,查看日志:

DEBUG [main] - ==>  Preparing: SELECT * FROM `user` WHERE id IN ( ? , ? , ? ) 
DEBUG [main] - ==> Parameters: 16(Integer), 22(Integer), 10(Integer)
DEBUG [main] - <==      Total: 3
User [id=10, username=张三, sex=1, birthday=Thu Jul 10 00:00:00 CST 2014, address=北京市]
User [id=16, username=张小明, sex=1, birthday=null, address=河南郑州]
User [id=22, username=陈小明, sex=1, birthday=null, address=河南郑州]

   

【注意】:拿到需求,可以先定义接口,然后在写sql。这样比较有头绪。

 

Mybatis动态sql

标签:app   管理   his   user   tor   ids   htm   方法   int   

人气教程排行