标签：prim code too tle and date bar 增加 primary
https://www.cnblogs.com/zjfjava/p/8882614.html
trim标记是一个格式化的标记，主要用于拼接sql的条件语句（前缀或后缀的添加或忽略），可以完成set或者是where标记的功能。
trim属性主要有以下四个
<update id="updateByPrimaryKey" parameterType="Object">
update student set
<trim suffixOverrides="," >
<if test="name != null ">
NAME=#{name},
</if>
<if test="hobby != null ">
HOBBY=#{hobby},
</if>
</trim> where id=#{id}
</update>
如果name和hobby的值都不为空的话，会执行如下语句
update student set NAME=‘XX‘,HOBBY=‘XX‘ /*,*/ where id=‘XX‘
会忽略最后一个“，” ；
<select id="selectByNameOrHobby" resultMap="BaseResultMap">
select * from student
<trim prefix="WHERE" prefixOverrides="AND | OR">
<if test="name != null and name.length()>0"> AND name=#{name}
</if>
<if test="hobby != null and hobby.length()>0"> AND hobby=#{hobby}
</if>
</trim>
</select>
如果name和hobby的值都不为空的话，会执行如下语句
select * from user WHERE /*and*/ name = ‘xx’ and hobby= ‘xx’
会为<trim>片段添加 "WHERE" 前缀，并忽略第一个 “and” ；
当然，避免出现“WHERE AND”还有其他方法，如下
<!--将where提取出来，并加上“1=1”的查询条件 -->
select * from student
where 1=1
<trim suffixOverrides=",">
<if test="name != null and name != ‘‘">
and NAME = #{name}
</if>
<if test="hobby != null and hobby != ‘‘">
and HOBBY = #{hobby}
</if>
</trim>
<insert id="insert" parameterType="Object">
insert into student <trim prefix="(" suffix=")" suffixOverrides="," >
<if test="name != null ">
NAME,
</if>
<if test="hobby != null ">
HOBBY,
</if>
</trim> <trim prefix="values(" suffix=")" suffixOverrides="," >
<if test="name != null ">
#{name},
</if>
<if test="hobby != null ">
#{hobby},
</if>
</trim>
</insert>
可以为生成格式正确的insert语句。
标签：prim code too tle and date bar 增加 primary
原文地址：https://www.cnblogs.com/yuluoxingkong/p/10178890.html
