1、普通的写法
<update id="updateBatch" parameterType="java.util.List">
<foreach collection="list" item="item" index="index" open="" close="" separator=";">
update course
<set>
name=${item.name}
</set>
where id = ${item.id}
</foreach>
</update>
一条记录update一次,性能比较差,容易造成阻塞。
MySQL没有提供直接的方法来实现批量更新,但可以使用case when语法来实现这个功能。
UPDATE course
SET name = CASE id
WHEN 1 THEN 'name1'
WHEN 2 THEN 'name2'
WHEN 3 THEN 'name3'
END,
title = CASE id
WHEN 1 THEN 'New Title 1'
WHEN 2 THEN 'New Title 2'
WHEN 3 THEN 'New Title 3'
END
WHERE id IN (1,2,3)
这条sql的意思是,如果id为1,则name的值为name1,title的值为New Title1;依此类推。
在Mybatis中的配置则如下:
2、
<update id="updateBatch" parameterType="list">
update course
<trim prefix="set" suffixOverrides=",">
<trim prefix="peopleId =case" suffix="end,">
<foreach collection="list" item="i" index="index">
<if test="i.peopleId!=null">
when id=#{i.id} then #{i.peopleId}
</if>
</foreach>
</trim>
<trim prefix=" roadgridid =case" suffix="end,">
<foreach collection="list" item="i" index="index">
<if test="i.roadgridid!=null">
when id=#{i.id} then #{i.roadgridid}
</if>
</foreach>
</trim>
<trim prefix="type =case" suffix="end," >
<foreach collection="list" item="i" index="index">
<if test="i.type!=null">
when id=#{i.id} then #{i.type}
</if>
</foreach>
</trim>
<trim prefix="unitsid =case" suffix="end," >
<foreach collection="list" item="i" index="index">
<if test="i.unitsid!=null">
when id=#{i.id} then #{i.unitsid}
</if>
</foreach>
</trim>
</trim>
where
<foreach collection="list" separator="or" item="i" index="index" >
id=#{i.id}
</foreach>
</update>
foreach的主要用在构建in条件中,它可以在SQL语句中进行迭代一个集合。foreach元素的属性主要有 item,index,collection,open,separator,close。item表示集合中每一个元素进行迭代时的别名,index指 定一个名字,用于表示在迭代过程中,每次迭代到的位置,open表示该语句以什么开始,separator表示在每次进行迭代之间以什么符号作为分隔 符,close表示以什么结束,在使用foreach的时候最关键的也是最容易出错的就是collection属性,该属性是必须指定的,但是在不同情况 下,该属性的值是不一样的,主要有一下3种情况:
下面分别来看看上述三种情况的示例代码:
1.单参数List的类型: <select id="dynamicForeachTest" resultType="Blog"> select * from t_blog where id in <foreach collection="list" index="index" item="item" open="(" separator="," close=")"> #{item} </foreach> </select> 上述collection的值为list,对应的Mapper是这样的 public List<Blog> dynamicForeachTest(List<Integer> ids); 测试代码: @Test public void dynamicForeachTest() { SqlSession session = Util.getSqlSessionFactory().openSession(); BlogMapper blogMapper = session.getMapper(BlogMapper.class); List<Integer> ids = new ArrayList<Integer>(); ids.add(1); ids.add(3); ids.add(6); List<Blog> blogs = blogMapper.dynamicForeachTest(ids); for (Blog blog : blogs) System.out.println(blog); session.close(); } 2.单参数array数组的类型: <select id="dynamicForeach2Test" resultType="Blog"> select * from t_blog where id in <foreach collection="array" index="index" item="item" open="(" separator="," close=")"> #{item} </foreach> </select> 上述collection为array,对应的Mapper代码: public List<Blog> dynamicForeach2Test(int[] ids); 对应的测试代码: @Test public void dynamicForeach2Test() { SqlSession session = Util.getSqlSessionFactory().openSession(); BlogMapper blogMapper = session.getMapper(BlogMapper.class); int[] ids = new int[] {1,3,6,9}; List<Blog> blogs = blogMapper.dynamicForeach2Test(ids); for (Blog blog : blogs) System.out.println(blog); session.close(); } 3.自己把参数封装成Map的类型 <select id="dynamicForeach3Test" resultType="Blog"> select * from t_blog where title like "%"#{title}"%" and id in <foreach collection="ids" index="index" item="item" open="(" separator="," close=")"> #{item} </foreach> </select> 上述collection的值为ids,是传入的参数Map的key,对应的Mapper代码: public List<Blog> dynamicForeach3Test(Map<String, Object> params); 对应测试代码: @Test public void dynamicForeach3Test() { SqlSession session = Util.getSqlSessionFactory().openSession(); BlogMapper blogMapper = session.getMapper(BlogMapper.class); final List<Integer> ids = new ArrayList<Integer>(); ids.add(1); ids.add(2); ids.add(3); ids.add(6); ids.add(7); ids.add(9); Map<String, Object> params = new HashMap<String, Object>(); params.put("ids", ids); params.put("title", "中国"); List<Blog> blogs = blogMapper.dynamicForeach3Test(params); for (Blog blog : blogs) System.out.println(blog); session.close(); }