mybatis之<trim prefix="" suffix="" suffixOverrides="" prefixOverrides=""></trim>

1. <trim prefix="" suffix="" suffixOverrides="" prefixOverrides=""></trim>
prefix:在trim标签内sql语句加上前缀。
suffix:在trim标签内sql语句加上后缀。
suffixOverrides:指定去除多余的后缀内容，如：suffixOverrides=","，去除trim标签内sql语句多余的后缀","。
prefixOverrides:指定去除多余的前缀内容

2.下面是一个往新闻表中插入数据的mybatis语句
<insert id="insertSelective" parameterType="com.cn.module.news.entity.SwapNews" >
insert into swap_news
<trim prefix="(" suffix=")" suffixOverrides="," >
<if test="id != null" >#{id,jdbcType=VARCHAR},</if>
<if test="id == null" >UUID(),</if>
<if test="type != null" >
type,
</if>
<if test="title != null" >
title,
</if>
<if test="stitle != null" >
stitle,
</if>
<if test="author != null" >
author,
</if>
<if test="souce != null" >
souce,
</if>
<if test="tags != null" >
tags,
</if>
<if test="summary != null" >
summary,
</if>
<if test="content != null" >
content,
</if>
<if test="picPath != null" >
pic_path,
</if>
<if test="remarks != null" >
remarks,
</if>
<if test="approvalFlag != null" >
approval_flag,
</if>
<if test="isTop != null" >
is_top,
</if>
<if test="delFlag != null" >
del_flag,
</if>
<if test="createUser != null" >
create_user,
</if>
<if test="createTime != null" >
create_time,
</if>
<if test="updateUser != null" >
update_user,
</if>
<if test="updateTime != null" >
update_time,
</if>
</trim>
<trim prefix="values (" suffix=")" suffixOverrides="," >
<if test="id != null" >
#{id,jdbcType=VARCHAR},
</if>
<if test="type != null" >
#{type,jdbcType=INTEGER},
</if>
<if test="title != null" >
#{title,jdbcType=VARCHAR},
</if>
<if test="stitle != null" >
#{stitle,jdbcType=VARCHAR},
</if>
<if test="author != null" >
#{author,jdbcType=VARCHAR},
</if>
<if test="souce != null" >
#{souce,jdbcType=VARCHAR},
</if>
<if test="tags != null" >
#{tags,jdbcType=VARCHAR},
</if>
<if test="summary != null" >
#{summary,jdbcType=VARCHAR},
</if>
<if test="content != null" >
#{content,jdbcType=LONGVARCHAR},
</if>
<if test="picPath != null" >
#{picPath,jdbcType=VARCHAR},
</if>
<if test="remarks != null" >
#{remarks,jdbcType=VARCHAR},
</if>
<if test="approvalFlag != null" >
#{approvalFlag,jdbcType=INTEGER},
</if>
<if test="isTop != null" >
#{isTop,jdbcType=INTEGER},
</if>
<if test="delFlag != null" >
#{delFlag,jdbcType=INTEGER},
</if>
<if test="createUser != null" >
#{createUser,jdbcType=VARCHAR},
</if>
<if test="createTime != null" >
#{createTime,jdbcType=TIMESTAMP},
</if>
<if test="updateUser != null" >
#{updateUser,jdbcType=VARCHAR},
</if>
<if test="updateTime != null" >
#{updateTime,jdbcType=TIMESTAMP},
</if>
</trim>
</insert>

假设没有指定

suffixOverrides=","

执行的sql语句也许是这样的：insert into swap_news(id,type,title,) values(1,2,哈哈哈,);显然是错误的

指定之后语句就会变成insert into swap_news(id,type,title,) values(1,2,哈哈哈);这样就将“，”去掉了。

前缀也是一个道理这里就不说了。