Mybatis 总结

1.如何传递多个参数

 mybatis中，如果接口有多个参数，那么在mapper.xml中，可以通过#{0,jdbcType=VARCHAR},#{1,jdbcType=VARCHAR}或#{param1,jdbcType=VARCHAR},#{param2,jdbcType=VARCHAR}来获取。

2.加强版的分支、选择判断

<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>

3.避免Where 空条件的尴尬

<select id="findActiveBlogLike" resultType="Blog">
 SELECT * FROM BLOG
 <where>
     <if test="state != null">
         and state = #{state}
     </if>
 </where> 
</select>

4.$与#的区别

1  select * from T_PRINT_LAYOUT where  D_RECID = ${recId}

最后生成的SQL为：

1 select * from T_PRINT_LAYOUT where  D_RECID = 1

即：直接将参数值替换到了原来${recId}的位置，相当于硬拼SQL

1  select * from T_PRINT_LAYOUT where  D_RECID = #{recid,jdbcType=DECIMAL}

最后生成的SQL为：

1 select * from T_PRINT_LAYOUT where  D_RECID = ?

即：#{...}被识别为一个SQL参数

参考：mybatis 使用经验小结