MyBatis之selectByExample与selectBy

mapper接口

List<Content> selectByExampleWithBLOBs(ContentExample example);
List<Content> selectByExample(ContentExample example);

mapper.xml

<select id="selectByExampleWithBLOBs" parameterType="com.ljf.blog.pojo.ContentExample" resultMap="ResultMapWithBLOBs">
    select
    <if test="distinct">
      distinct
    </if>
    <include refid="Base_Column_List" />
    ,
    <include refid="Blob_Column_List" />
    from t_contents
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
    <if test="orderByClause != null">
      order by ${orderByClause}
    </if>
</select>

<select id="selectByExample" parameterType="com.ljf.blog.pojo.ContentExample" resultMap="BaseResultMap">
    select
    <if test="distinct">
      distinct
    </if>
    <include refid="Base_Column_List" />
    from t_contents
    <if test="_parameter != null">
      <include refid="Example_Where_Clause" />
    </if>
    <if test="orderByClause != null">
      order by ${orderByClause}
    </if>
</select>

两段SQL查询返回的resultMap不同，一个是BaseResultMap，另一个是ResultMapWithBLOBs

<resultMap id="BaseResultMap" type="com.ljf.blog.pojo.Content">
    <id column="cid" jdbcType="INTEGER" property="cid" />
    <result column="title" jdbcType="VARCHAR" property="title" />
    <result column="slug" jdbcType="VARCHAR" property="slug" />
    <result column="created" jdbcType="INTEGER" property="created" />
    <result column="modified" jdbcType="INTEGER" property="modified" />
    <result column="author_id" jdbcType="INTEGER" property="authorId" />
    <result column="type" jdbcType="VARCHAR" property="type" />
    <result column="status" jdbcType="VARCHAR" property="status" />
    <result column="tags" jdbcType="VARCHAR" property="tags" />
    <result column="categories" jdbcType="VARCHAR" property="categories" />
    <result column="thumbImg" jdbcType="VARCHAR" property="thumbimg" />
    <result column="hits" jdbcType="INTEGER" property="hits" />
    <result column="comments_num" jdbcType="INTEGER" property="commentsNum" />
    <result column="allow_comment" jdbcType="BIT" property="allowComment" />
    <result column="allow_ping" jdbcType="BIT" property="allowPing" />
    <result column="allow_feed" jdbcType="BIT" property="allowFeed" />
</resultMap>
<resultMap extends="BaseResultMap" id="ResultMapWithBLOBs" type="com.ljf.blog.pojo.Content">
    <result column="content" jdbcType="LONGVARCHAR" property="content" />
</resultMap>

• ResultMapWithBLOBs 定义时，继承了BaseResultMap，并且自己特殊的字段，该字段通常是longvarchar类型，本例中content就为特殊字段。
• content字段类型为text。故如需检索的字段中包含大字段类型时，必须用selectByExampleWithBLOBs，不检索大字段时，用selectByExample就足够了。update同样如此。

文章表 t_contents