<resultMap>是Maybatis的結(jié)果集封裝，搭配<select><association>等標(biāo)簽的resultMap屬性使用屬性：id:該封裝規(guī)則的唯一標(biāo)識type:封裝出來的類型，可以是jdk自帶的，比如Map，應(yīng)該可以是自定義的，比如EmployeeautoMapping:自動封裝，如果數(shù)據(jù)庫字段和javaBean的字段名一樣，可以使用這種方式，但是不建議采取，還是老老實實寫比較穩(wěn)妥，如果非要使用此功能，那就在全局配置中加上mapUnderscoreToCamelCase=TRUE，它會使經(jīng)典數(shù)據(jù)庫字段命名規(guī)則翻譯成javaBean的經(jīng)典命名規(guī)則，如：a_column翻譯成aColumnextends:繼承其他封裝規(guī)則，和Java中的繼承一樣，也特別適合這樣的場景子標(biāo)簽：<id>用來標(biāo)識出對象的唯一性，比如用表的主鍵，如：<id column="employee_id" property="empId"/>column指定數(shù)據(jù)庫字段名或者其別名property指定javaBean的屬性名還有jdbcType,javaType,typeHandler,分別數(shù)據(jù)庫類型，屬性的java類型，數(shù)據(jù)庫與Java類型匹配處理器默認的類型匹配處理器有：145012_VWtp_3049601.png以上羅列的資料不全，可以參考官方文檔的如下章節(jié)145150_qXkB_3049601.png<result>非主鍵的映射規(guī)則<result column="dept_name" property="deptName"/><association>屬性：property:同<id>標(biāo)簽javaType:同<id>標(biāo)簽select:指定嵌套SQL，可以是本XML或者其他XML文件中的<select>fetchType:延遲加載，lazy打開延遲加載;eager積極加載column:同<id>標(biāo)簽resultMap:不使用嵌套SQL，而是使用復(fù)雜SQL一次取出關(guān)聯(lián)的對象，并封裝，對應(yīng)下面的方式三resultSet:引用根據(jù)<select>標(biāo)簽得到的resultSets，如：SELECT * FROM BLOG WHERE ID = #{id}SELECT * FROM AUTHOR WHERE ID = #{id} <select id="selectBlog" resultSets="blogs,authors" resultMap="blogResult" statementType="CALLABLE">{call getBlogsAndAuthors(#{id,jdbcType=INTEGER,mode=IN})} </select> <resultMap id="blogResult" type="Blog"><id property="id" column="id" /><result property="title" column="title"/><association property="author" javaType="Author" resultSet="authors" column="author_id" foreignColumn="id"><id property="id" column="id"/><result property="username" column="username"/><result property="password" column="password"/><result property="email" column="email"/><result property="bio" column="bio"/></association> </resultMap>autoMapping:同<id>標(biāo)簽columnPrefix:關(guān)聯(lián)多張表查詢時，為了使列明不重復(fù)，使用此功能可以減少開發(fā)量<select id="selectBlog" resultMap="blogResult">selectB.id as blog_id,B.title as blog_title,A.id as author_id,A.username as author_username,A.password as author_password,A.email as author_email,A.bio as author_bio,CA.id as co_author_id,CA.username as co_author_username,CA.password as co_author_password,CA.email as co_author_email,CA.bio as co_author_biofrom Blog Bleft outer join Author A on B.author_id = A.idleft outer join Author CA on B.co_author_id = CA.idwhere B.id = #{id} </select> 抽取出共同的resultMap，因為作者和其他作者都具有同樣的屬性，因此有：<resultMap id="authorResult" type="Author"><id property="id" column="author_id"/><result property="username" column="author_username"/><result property="password" column="author_password"/><result property="email" column="author_email"/><result property="bio" column="author_bio"/> </resultMap> <resultMap id="blogResult" type="Blog"><id property="id" column="blog_id" /><result property="title" column="blog_title"/><association property="author"resultMap="authorResult" /><association property="coAuthor"resultMap="authorResult"columnPrefix="co_" /> </resultMap>foreignColumn:外鍵列notNullColumn:不為空的列，如果指定了列，那么只有當(dāng)字段不為空時，Mybatis才會真正創(chuàng)建對象，才能得到我們想要的值typeHandler:同<id>標(biāo)簽方式一：<!-- 嵌套方式 --><resultMap type="com.jv.bean.Employee" id="EmpAndDeptMethod2"><id column="employee_id" property="employeeId"/><result column="first_name" property="firstName"/><result column="last_name" property="lastName"/><result column="gendor" property="gendor"/><result column="birthday" property="birthday"/><!-- 可以將下面這部分抽離出來單獨使用一個resultMap進行標(biāo)記，然后在association標(biāo)簽中使用resultMap指向該標(biāo)記 --><association property="dept" javaType="com.jv.bean.DepartMent"><id column="dept_id" property="deptId"/><result column="dept_name" property="deptName"/><result column="dept_desc" property="deptDesc"/></association></resultMap><select id="getEmployeeDetailInfo2" resultMap="EmpAndDeptMethod2">select employee_id,first_name,last_name,gendor,birthday,a.dept_id,dept_name,dept_desc from employee a,department bwhere a.dept_id=b.dept_idand a.employee_id=#{id}</select>方式二：<!-- 分布查詢 --><!-- 該功能有一個很重要的用途：可以支持延遲加載（按需加載），需要在全局配置文件中增加： lazyLoadingEnabled 打開延遲加載aggressiveLazyLoading 設(shè)置為TRUE是使用時全部加載，false是按需加載這兩個配置。--><resultMap type="com.jv.bean.Employee" id="EmpAndDeptMethod3"><id column="employee_id" property="employeeId"/><result column="first_name" property="firstName"/><result column="last_name" property="lastName"/><result column="gendor" property="gendor"/><result column="birthday" property="birthday"/><association property="dept"select="com.jv.dao.DepartMentMapper.getDepartMentByIdNew" column="dept_id"></association><association property="post"select="com.jv.dao.PostMapper.getPostById" column="post_id"></association></resultMap><select id="getEmployeeDetailInfo3" resultMap="EmpAndDeptMethod3">select employee_id,first_name,last_name,gendor,birthday,dept_id,post_idfrom employee awhere a.employee_id=#{id}</select>方式三：<!-- 嵌套方式 --><resultMap type="com.jv.bean.Employee" id="EmpAndDeptMethod2"><id column="employee_id" property="employeeId"/><result column="first_name" property="firstName"/><result column="last_name" property="lastName"/><result column="gendor" property="gendor"/><result column="birthday" property="birthday"/><!-- 可以將下面這部分抽離出來單獨使用一個resultMap進行標(biāo)記，然后在association標(biāo)簽中使用resultMap指向該標(biāo)記 --><association property="dept" resultMap="deptMap"></association></resultMap><resultMap id="deptMap" javaType="com.jv.bean.DepartMent"><id column="dept_id" property="deptId"/><result column="dept_name" property="deptName"/><result column="dept_desc" property="deptDesc"/></resultMap><select id="getEmployeeDetailInfo2" resultMap="EmpAndDeptMethod2">select employee_id,first_name,last_name,gendor,birthday,a.dept_id,dept_name,dept_desc from employee a,department bwhere a.dept_id=b.dept_idand a.employee_id=#{id}</select><collection>和association很像，collection是負責(zé)處理多行的結(jié)果集，如：方式一：使用嵌套SQL<resultMap id="blogResult" type="Blog"><collection property="posts" javaType="ArrayList" column="id" ofType="Post" select="selectPostsForBlog"/> </resultMap><select id="selectBlog" resultMap="blogResult">SELECT * FROM BLOG WHERE ID = #{id} </select><select id="selectPostsForBlog" resultType="Post">SELECT * FROM POST WHERE BLOG_ID = #{id} </select>方式二：使用復(fù)雜查詢-在collection中直接配置封裝規(guī)則<select id="selectBlog" resultMap="blogResult">selectB.id as blog_id,B.title as blog_title,B.author_id as blog_author_id,P.id as post_id,P.subject as post_subject,P.body as post_body,from Blog Bleft outer join Post P on B.id = P.blog_idwhere B.id = #{id} </select> <resultMap id="blogResult" type="Blog"><id property="id" column="blog_id" /><result property="title" column="blog_title"/><collection property="posts" ofType="Post"><id property="id" column="post_id"/><result property="subject" column="post_subject"/><result property="body" column="post_body"/></collection> </resultMap>方式三：使用復(fù)雜查詢-抽取封裝規(guī)則放到resultMap中<select id="selectBlog" resultMap="blogResult">selectB.id as blog_id,B.title as blog_title,B.author_id as blog_author_id,P.id as post_id,P.subject as post_subject,P.body as post_body,from Blog Bleft outer join Post P on B.id = P.blog_idwhere B.id = #{id} </select> <resultMap id="blogResult" type="Blog"><id property="id" column="blog_id" /><result property="title" column="blog_title"/><collection property="posts" ofType="Post" resultMap="blogPostResult" columnPrefix="post_"/> </resultMap><resultMap id="blogPostResult" type="Post"><id property="id" column="id"/><result property="subject" column="subject"/><result property="body" column="body"/> </resultMap>方式二和方式三只有在封裝的方式上有區(qū)別<descriminator>負責(zé)根據(jù)返回的字段的值封裝不同的類型，如：<resultMap id="vehicleResult" type="Vehicle"><id property="id" column="id" /><result property="vin" column="vin"/><result property="year" column="year"/><result property="make" column="make"/><result property="model" column="model"/><result property="color" column="color"/><discriminator javaType="int" column="vehicle_type"><case value="1" resultMap="carResult"/><case value="2" resultMap="truckResult"/><case value="3" resultMap="vanResult"/><case value="4" resultMap="suvResult"/></discriminator> </resultMap> <resultMap id="carResult" type="Car" extends="vehicleResult"><result property="doorCount" column="door_count" /> </resultMap>上面的配置就是如果vehicle_type的值是1，那么封裝的結(jié)果為carResult，同事carResult又繼承了vehicleResult的所有普通封裝規(guī)則，最后的它結(jié)果可以按照下面的配置理解<resultMap id="carResult" type="Vehicle"><id property="id" column="id" /><result property="vin" column="vin"/><result property="year" column="year"/><result property="make" column="make"/><result property="model" column="model"/><result property="color" column="color"/><result property="doorCount" column="door_count"/> </resultMap><constructor>使用構(gòu)造器注入屬性值，可能會問既然通過<id>和<result>就可以給屬性注入值了，為什么還有一個構(gòu)造器注入的，原因是有的JavaBean沒有提供屬性的getter和setter方法。<constructor><idArg column="id" javaType="int" name="id" /><arg column="age" javaType="_int" name="age" /><arg column="username" javaType="String" name="username" /> </constructor> 為了維護更方便，推薦在使用構(gòu)造器注入的時候加上name屬性，該屬性值與構(gòu)造器參數(shù)名字相同（需要編譯參數(shù)加上-parameters，Jdk版本為1.8，而且Mybatis的參數(shù)useActualParamName設(shè)置為true(默認值為true)），也可以使用@param("paramName")指定特殊的參數(shù)名。轉(zhuǎn)載于:https://my.oschina.net/u/3049601/blog/1613921

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