MyBatis經常使用標籤

• 動態 SQL

  • if 條件判斷

    <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>

  • choose (when, otherwise)條件查詢

    <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>

  • trim (where, set)

    • where：元素只會在至少有一個子元素的條件返回 SQL 子句的狀況下才去插入「WHERE」子句。並且，若語句的開頭爲「AND」或「OR」，where 元素也會將它們去除。

      <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:經過自定義 trim 元素來定製 where 元素的功能

      <trim prefix="WHERE" prefixOverrides="AND |OR ">
      ... 
      </trim>

    • set:元素能夠用於動態包含須要更新的列，而捨去其它的

      <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>

  • foreach：對一個集合進行遍歷，一般是在構建 IN 條件語句的時候

    <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>

  • bind：元素能夠從 OGNL 表達式中建立一個變量並將其綁定到上下文

    <select id="selectBlogsLike" resultType="Blog">
        <bind name="pattern" value="'%' + _parameter.getTitle() + '%'" />
        SELECT * FROM BLOG
        WHERE title LIKE #{pattern}
    </select>