一.更新多条数据,每条数据都不一样
背景描述:通常如果需要一次更新多条数据有两个方式,(1)在业务代码中循环遍历逐条更新。(2)一次性更新所有数据(更准确的说是一条sql语句来更新所有数据,逐条更新的操作放到数据库端,在业务代码端展现的就是一次性更新所有数据)。两种方式各有利弊,下面将会对两种方式的利弊做简要分析,主要介绍第二种方式在mybatis中的实现。
1.逐条更新(java实现)
这种方式显然是最简单,也最不容易出错的,即便出错也只是影响到当条出错的数据,而且可以对每条数据都比较可控,更新失败或成功,从什么内容更新到什么内容,都可以在逻辑代码中获取。代码可能像下面这个样子:
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updateBatch(List<MyData> datas){ for (MyData data : datas){ try { myDataDao.update(data); //更新一条数据,mybatis中如下面的xml文件的update } catch (Exception e){ ... //如果更新失败可以做一些其他的操作,比如说打印出错日志等 } } } //mybatis中update操作的实现 <update> update mydata set ... where ... </update> |
这种方式最大的问题就是效率问题,逐条更新,每次都会连接数据库,然后更新,再释放连接资源(虽然通过连接池可以将频繁连接数据的效率大大提高,抗不住数据量大),这中损耗在数据量较大的时候便会体现出效率问题。这也是在满足业务需求的时候,通常会使用上述提到的第二种批量更新的实现(当然这种方式也有数据规模的限制,后面会提到)。
2.逐条更新(mybatis实现)
通过循环,依次执行多条update的sql
前提条件:
要实现批量更新,首先得设置mysql支持批量操作,在jdbc链接中需要附加&allowMultiQueries=true属性才行
例如:
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jdbc:mysql://localhost:3306/dbname?characterEncoding=utf8&zeroDateTimeBehavior=convertToNull&allowMultiQueries=true |
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< 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。
3.sql批量更新(主力实现)
(1)、实际实践(传入的是List<Map<String, Object>>)
务必注意:一定要加where条件,里面的id为需要更新的数据的id;如果不加where条件,则会全部更新,但是需要更新且有数据的更新为传递的数据,没有数据的则更新为null,此时更新出错
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< update id = "updateChartParamByAccountAndChartid" parameterType = "list" > update followme_parameters < trim prefix = "set" suffixOverrides = "," > < trim prefix = "signal_source =case" suffix = "end," > < foreach collection = "list" item = "item" index = "index" > < if test = "item.signalSource!=null" > when account=#{item.account} and chart_id=#{item.chartId} then #{item.signalSource} </ if > </ foreach > </ trim > < trim prefix = "rate =case" suffix = "end," > < foreach collection = "list" item = "item" index = "index" > < if test = "item.rate!=null" > when account=#{item.account} and chart_id=#{item.chartId} then #{item.rate} </ if > </ foreach > </ trim > </ trim > where id in < foreach collection = "list" item = "item" index = "index" separator = "," open = "(" close = ")" > #{item.id} </ foreach > </ update > |
另外文章的样板
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< 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 > |
(2)、下面逐步讲解
一条sql语句来批量更新所有数据,下面直接看一下在mybatis中通常是怎么写的(去掉mybatis语法就是原生的sql语句了,所有就没单独说sql是怎么写的)。
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< update id = "updateBatch" parameterType = "java.util.List" > update mydata_table set status= < foreach collection = "list" item = "item" index = "index" separator = " " open = "case ID" close = "end" > when #{item.id} then #{item.status} </ foreach > where id in < foreach collection = "list" index = "index" item = "item" separator = "," open = "(" close = ")" > #{item.id,jdbcType=BIGINT} </ foreach > </ update > |
其中when...then...是sql中的"switch" 语法。这里借助mybatis的语法来拼凑成了批量更新的sql,上面的意思就是批量更新id在updateBatch参数所传递List中的数据的status字段。还可以使用实现同样的功能,代码如下:
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< update id = "updateBatch" parameterType = "java.util.List" > update mydata_table < trim prefix = "set" suffixOverrides = "," > < trim prefix = "status =case" suffix = "end," > < foreach collection = "list" item = "item" index = "index" > when id=#{item.id} then #{item.status} </ foreach > </ trim > </ trim > where id in < foreach collection = "list" index = "index" item = "item" separator = "," open = "(" close = ")" > #{item.id,jdbcType=BIGINT} </ foreach > </ update > < trim > |
属性说明
1.prefix,suffix 表示在trim标签包裹的部分的前面或者后面添加内容
2.如果同时有prefixOverrides,suffixOverrides 表示会用prefix,suffix覆盖Overrides中的内容。
3.如果只有prefixOverrides,suffixOverrides 表示删除开头的或结尾的xxxOverides指定的内容。
上述代码转化成sql如下:
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update mydata_table set status = case when id = #{item.id} then #{item.status} //此处应该是<foreach>展开值 ... end where id in (...); |
当然这是最简单的批量更新实现,有时候可能需要更新多个字段,那就需要将
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< trim prefix = "status =case" suffix = "end," > < foreach collection = "list" item = "item" index = "index" > when id=#{item.id} then #{item.status} </ foreach > </ trim > |
复制拷贝多次,更改prefix和when...then...的内容即可.而如果当需要为某个字段设置默认值的时候可以使用else
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< trim prefix = "status =case" suffix = "end," > < foreach collection = "list" item = "item" index = "index" > when id=#{item.id} then #{item.status} </ foreach > else default_value </ trim > |
还有更常见的情况就是需要对要更新的数据进行判断,只有符合条件的数据才能进行更新,这种情况可以这么做:
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< trim prefix = "status =case" suffix = "end," > < foreach collection = "list" item = "item" index = "index" > < if test = "item.status !=null and item.status != -1" > when id=#{item.id} then #{item.status} </ if > </ foreach > </ trim > |
这样的话只有要更新的list中status != null && status != -1的数据才能进行status更新.其他的将使用默认值更新,而不会保持原数据不变.如果要保持原数据不变呢?即满足条件的更新,不满足条件的保持原数据不变,简单的来做就是再加一个,因为mybatis中没有if...else...语法,但可以通过多个实现同样的效果,如下:
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< trim prefix = "status =case" suffix = "end," > < foreach collection = "list" item = "item" index = "index" > < if test = "item.status !=null and item.status != -1" > when id=#{item.id} then #{item.status} </ if > < if test = "item.status == null or item.status == -1" > when id=#{item.id} then mydata_table.status //这里就是原数据 </ if > </ foreach > </ trim > |
整体批量更新的写法如下:
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< update id = "updateBatch" parameterType = "java.util.List" > update mydata_table < trim prefix = "set" suffixOverrides = "," > < trim prefix = "status =case" suffix = "end," > < foreach collection = "list" item = "item" index = "index" > < if test = "item.status !=null and item.status != -1" > when id=#{item.id} then #{item.status} </ if > < if test = "item.status == null or item.status == -1" > when id=#{item.id} then mydata_table.status//原数据 </ if > </ foreach > </ trim > </ trim > where id in < foreach collection = "list" index = "index" item = "item" separator = "," open = "(" close = ")" > #{item.id,jdbcType=BIGINT} </ foreach > </ update > |
4.批量更新(单个字段,传参list),实际是sql批量更新的简化版本而已
(1)、单个字段方法1
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< update id = "updateByBatch" parameterType = "java.util.List" > update t_goods set NODE_ID= < foreach collection = "list" item = "item" index = "index" separator = " " open = "case" close = "end" > when GOODS_ID=#{item.goodsId} then #{item.nodeId} </ foreach > where GOODS_ID in < foreach collection = "list" index = "index" item = "item" separator = "," open = "(" close = ")" > #{item.goodsId,jdbcType=BIGINT} </ foreach > </ update > |
(2)、单个字段方法2
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< update id = "updateByBatch" parameterType = "java.util.List" > UPDATE t_goods SET NODE_ID = CASE < foreach collection = "list" item = "item" index = "index" > WHEN GOODS_ID = #{item.goodsId} THEN #{item.nodeId} </ foreach > END WHERE GOODS_ID IN < foreach collection = "list" index = "index" item = "item" open = "(" separator = "," close = ")" > #{item.goodsId} </ foreach > </ update > |
以上单字段更新实际执行:
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UPDATE t_goods SET NODE_ID = CASE WHEN GOODS_ID = ? THEN ? END WHERE GOODS_ID IN ( ? ) |
5.sql批量更新(通过insert实现)
传入的是List<Map<String,Object>>
直接运行插入,如果有插入的数据转为更新该条数据
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< insert id = "updateChartParamByAccountAndChartid" > insert into followme_parameters (account,chart_id,signal_source,rate) values < foreach collection = "list" separator = "," index = "index" item = "item" > (#{item.account},#{item.chartId},#{item.signalSource},#{item.rate}) </ foreach > ON duplicate KEY UPDATE signal_source=values(signal_source),rate=values(rate) </ insert > |
二.更新多条数据,更新的内容一样.
1.传map/传String
NODE_ID从map中取出来,goodsIdList是字符串拼接好的(如下面的"1,2,5")
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< update id = "updateByBatchPrimaryKey" parameterType = "java.util.Map" > UPDATE t_goods SET NODE_ID = #{nodeId} WHERE GOODS_ID IN (${goodsIdList}) </ update > |
实际的sql
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UPDATE t_goods SET NODE_ID = ? WHERE GOODS_ID IN ( 1 , 2 , 5 ); |
2.传map/传list
NODE_ID从map中取出来,goodsIdList是用list拼接出来的
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< update id = "updateByBatchPrimaryKey" parameterType = "java.util.Map" > UPDATE t_goods SET NODE_ID = #{nodeId} WHERE GOODS_ID IN < foreach collection = "list" index = "index" item = "item" open = "(" separator = "," close = ")" > #{item.goodsId} </ foreach > </ update > |
实际的sql
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UPDATE t_goods SET NODE_ID = ? WHERE GOODS_ID IN ( 1 , 2 , 5 ); |
参考文章:
主力:https://blog.csdn.net/xyjawq1/article/details/74129316/
辅助:https://www.jianshu.com/p/041bec8ae6d3
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原文链接:https://www.cnblogs.com/eternityz/p/12284760.html