标签：gsl 后缀 nec alt 意义 一个 通用 otherwise 允许
1、动态SQL的元素：
<select id="findActiveBlogWithTitleLike" resultType="Blog">
SELECT * FROM BLOG
WHERE state = ‘ACTIVE’
<if test="title != null">
AND title like #{title}
</if>
</select>
<select id="findActiveBlogLike" resultType="Blog">
SELECT * FROM BLOG WHERE state = ‘ACTIVE’
<if test="title != null">
AND title like #{title}
</if>
<if test="author != null and author.name != null">
AND author_name like #{author.name}
</if>
</select>
<select id="findActiveBlogLike"
resultType="Blog">
SELECT * FROM BLOG WHERE state = ‘ACTIVE’
<choose>
<when test="title != null">
AND title like #{title}
</when>
<when test="author != null and author.name != null">
AND author_name like #{author.name}
</when>
<otherwise>
AND featured = 1
</otherwise>
</choose>
</select>
<select id="findActiveBlogLike" resultType="Blog">
SELECT * FROM BLOG
WHERE
<if test="state != null">
state = #{state}
</if>
<if test="title != null">
AND title like #{title}
</if>
<if test="author != null and author.name != null">
AND author_name like #{author.name}
</if>
</select>
如果这些条件都没有匹配上将会发生什么?这条 SQL 结束时就会成这样:
SELECT * FROM BLOG WHERE
这会导致查询失败。如果仅仅第二个条件匹配是什么样的?这条 SQL 结束时就会是这 样:
SELECT * FROM BLOG WHERE AND title like ‘someTitle’
这个查询也会失败。这个问题不能简单的用条件来解决,如果你从来没有这样写过,那 么你以后也不会这样来写。
MyBatis 有一个简单的处理,这在 90%的情况下都会有用。而在不能使用的地方,你可 以自定义处理方式。加上一个简单的改变,所有事情都会顺利进行:
<select id="findActiveBlogLike" resultType="Blog">
SELECT * FROM BLOG
<where>
<if test="state != null">
state = #{state}
</if>
<if test="title != null">
AND title like #{title}
</if>
<if test="author != null and author.name != null">
AND author_name like #{author.name}
</if>
</where>
</select>
<trim prefix="WHERE" prefixOverrides="AND |OR "> ... </trim>
<update id="updateAuthorIfNecessary">
update Author
<set>
<if test="username != null">username=#{username},</if>
<if test="password != null">password=#{password},</if>
<if test="email != null">email=#{email},</if>
<if test="bio != null">bio=#{bio}</if>
</set>
where id=#{id}
</update>
<trim prefix="SET" suffixOverrides=","> ... </trim>
<select id="selectPostIn" resultType="domain.blog.Post">
SELECT *
FROM POST P
WHERE ID in
<foreach item="item" index="index" collection="list"
open="(" separator="," close=")">
#{item}
</foreach>
</select>
<select id="selectBlogsLike" resultType="Blog">
<bind name="pattern" value="‘%‘ + _parameter.getTitle() + ‘%‘" />
SELECT * FROM BLOG
WHERE title LIKE #{pattern}
</select>
标签：gsl 后缀 nec alt 意义 一个 通用 otherwise 允许
原文地址：http://www.cnblogs.com/hsa521/p/7678402.html
