Mybatis Mapper xml映射配置知识总结

 写的很乱，可以参照着比较完整的看。

 

 

 1、 
SQL映射文件中的顶级元素

  
cache –
配置给定命名空间的缓存。
         <cache
                  eviction="FIFO"
                  flushInterval="60000"
                  size="512"
        readOnly="true"/>
 
   cache-ref –
从其他命名空间引用缓存配置。
          <cache-ref namespace="com.someone.application.data.SomeMapper"/>
 
   resultMap
– 最复杂,也是最有力量的元素,用来描述如何从数据库结果集中来加
载你的对象。
          <resultMap id="userResultMap" type="User">
          <id property="id" column="user_id" />
          <result property="username" column="username"/>
           <result property="password" column="password"/>
          </resultMap>
             引用它的语句使用 resultMap 属性就行了(注意我们去掉了 resultType 属性)。比如:
          <select id="selectUsers" parameterType="int" resultMap="userResultMap">
                 select user_id, user_name, hashed_password
                 from some_table
                where id = #{id}
           </select>
 
          sql
– 可以重用的
SQL 块,也可以被其他语句引用。
                  这个元素可以被用来定义可重用的 SQL 代码段,可以包含在其他语句中。比如:
                         <sql id="userColumns"> id,username,password </sql>
                  这个 SQL 片段可以被包含在其他语句中,例如:
                    <select id="selectUsers" parameterType="int" resultType="hashmap">
                                        select <include refid="userColumns"/>
                                        from some_table
                                       where id = #{id}
                   </select>
 
          insert
– 映射插入语句
                      <insert id="insertAuthor" parameterType="domain.blog.Author">
                               insert into Author (id,username,password,email,bio)
                               values (#{id},#{username},#{password},#{email},#{bio})
                        </insert>
           update
– 映射更新语句
                        <update id="updateAuthor" parameterType="domain.blog.Author">
                                update Author set
                                     username = #{username},
                                    password = #{password},
                                    email = #{email},
                                    bio = #{bio}
                          where id = #{id}
                    </update>
 
            delete
– 映射删除语句
                   <delete id="deleteAuthor" parameterType="int">
                                delete from Author where id = #{id}
                     </delete>
 
              select
– 映射查询语句
                
<select id="selectPerson" parameterType="int" resultType="java.util.HashMap">
                                 SELECT * FROM PERSON WHERE ID = #{id}
                       </select>
                          (与Ibaits不同的是参数注释方式由#id#变为#{id},parameterClass变为parameterType，resultClass 变为resultType)
2、 动态SQL
 
              if
                 在动态 SQL 中所做的最通用的事情是包含部分 where 字句的条件。比如:
                           <select id="findActiveBlogWithTitleLike"
                                  parameterType="Blog" resultType="Blog">
                                          SELECT * FROM BLOG
                                          WHERE state = ‘ACTIVE’
                                   <if test="title != null">
                                             AND title like #{title}
                                  </if>
                              </select>
 
            choose, when, otherwise
 
                  <select id="findActiveBlogLike"
                                 
c4ba
 parameterType="Blog" 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
 
                 <select id="findActiveBlogLike"
                                  parameterType="Blog" 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>
 
                 如果 where 元素没有做出你想要的,你可以使用 trim 元素来自定义。比如,和 where 元素相等的
                 trim 元素是:
                                  <trim prefix="WHERE" prefixOverrides="AND |OR ">
                                  ...
                                  </trim>
 
                      set 元素可以被用于动态包含更新的列,而不包含不需更新的。
                 比如:
                                  <update id="updateAuthorIfNecessary"
                                      parameterType="domain.blog.Author">
                                     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
                 另外一个动态 SQL 通用的必要操作是迭代一个集合, 通常是构建在 IN 条件中的。 比如:
                                  <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>