Mybatis之动态sql

	/**
	 * 更新数据，比如密码或者年龄
	 * @param user  User对象，其中封装了用户密码或者用户的年龄
	 * @return 受影响的行数，成功返回1，否则返回0
	 */
	Integer update(User user);

 	<update id="update" parameterType="cn.tedu.spring.entity.User">
	 	update user 
	 	set
	 	<if test="password!=null">
	 		password=#{password}
	 	</if>
	 	<if test="age!=null">
	 		age=#{age}
	 	</if>
	 	where id=#{id}
	 </update>

	@Test
	public void testUpdate() {
		//加载Spring的配置文件
		AbstractApplicationContext ac
			= new ClassPathXmlApplicationContext(
				"spring-mvc.xml",
				"spring-dao.xml");
		
		//获取UserMapper的bean，这个是spring通过扫描mapper.xml文件自动为mybatis自动创建的，首字母小写
		UserMapper userMapper
			= ac.getBean(
				"userMapper", UserMapper.class);
		//新建一个User对象
		User user=new User();
		user.setId(3);  //设置id
		user.setAge(33);  //设置年龄
		int affectRows=userMapper.update(user);
		System.out.println(affectRows);
		ac.close();
	}

	/**
	 * 查找用户信息，根据用户名或者用户id查询
	 * @param user  User对象，其中封装了用户名或者用户id
	 * @return 用户对象
	 */
	User findUser(User user);

<!-- 
		User findUser(User user); 
		不能同时查询，缺少连接符号 and or
	-->
	<select id="findUser" parameterType="cn.tedu.spring.entity.User" resultType="cn.tedu.spring.entity.User">
		select * from user 
		where 
		<if test="id!=null">
			id=#{id}
		</if>
		
		<if test="username!=null">
			username=#{username}
		</if>
		
	</select>

@Test
	public void testFind() {
		//加载Spring的配置文件
		AbstractApplicationContext ac
			= new ClassPathXmlApplicationContext(
				"spring-mvc.xml",
				"spring-dao.xml");
		
		//获取UserMapper的bean，这个是spring通过扫描mapper.xml文件自动为mybatis自动创建的，首字母小写
		UserMapper userMapper
			= ac.getBean(
				"userMapper", UserMapper.class);
		//新建一个User对象
		User user=new User();
		user.setId(3);  //设置id
		//根据id查找
		System.out.println(userMapper.findUser(user));
		ac.close();
	}

<select>
	select * from user where
    <choose>
    	<when test="password!=null">
        	password=#{password}
        </when>
        
        <otherwise>
        	id=#{id}
        </otherwise>
    </choose>
</select>

<select id="findUser" parameterType="cn.tedu.spring.entity.User" resultType="cn.tedu.spring.entity.User" >
	select * from user 
    where 
    <if test="password!=null">
    	password=#{password}
    </if>
    
    <if test="username!=null">
    	and username=#{username}
    </if>
    
</select>

select 字段 from 表名
	<where>
		.....
	</where>

<select id="findUser" parameterType="cn.tedu.spring.entity.User" resultType="cn.tedu.spring.entity.User" >
	select * from user 
    <where>
        <if test="password!=null">
           and password=#{password}
        </if>

        <if test="username!=null">
            and username=#{username}
        </if>
    </where>
    
</select>

<update id="update" parameterType="cn.tedu.spring.entity.User">
	 	update user 
	 	set
	 	<if test="password!=null">
	 		password=#{password},
	 	</if>
	 	
	 	<if test="age!=null">
	 		age=#{age},
	 	</if>
	 	
	 	<if test="username!=null">
	 		username=#{username}
	 	</if>
	 	
	 	where id=#{id}
	 </update>

update table_name 
	<set>
		......
	</set>

<update id="update" parameterType="cn.tedu.spring.entity.User">
	 	update user 
	 	<set>
            <if test="password!=null">
                password=#{password},
            </if>

            <if test="age!=null">
                age=#{age},
            </if>

            <if test="username!=null">
                username=#{username}
            </if>
	 	</set>
	 	where id=#{id}
	 </update>