三. 根据员工编号嵌套result 查询。
为了根据不同的情况，可以查询出不同的结果，那么需要将sex 当成一个参数传递进去。
UserMapper.java 提供接口:
public User getUserByIdWithResultString(@Param(value="id") int id, @Param(value="sex") String sex);
UserMapper.xml sql语句:
<resultMap type="user" id="userResultMapWithDiscriminatorResult"> <!-- 员工的基本属性。 --> <id property="id" column="id"/> <result property="name" column="name"/> <result property="sex" column="sex"/> <result property="age" column="age"/> <result property="description" column="description"/> <!-- 分类选择 --> <discriminator javaType="string" column="sex"> <case value="男" resultMap="boyHealthyMapWithResult"></case> <case value="女" resultMap="girlHealthyMapWithResult"></case> </discriminator> </resultMap> <select id="getUserByIdWithResultString" resultMap="userResultMapWithDiscriminatorResult"> <!--因为表中id,description 等大量字段重复，为了保证不被合并，这里要用别名进行区分。--> select u.id as id,u.name as name,u.sex as sex,u.age as age,u.description as description, b.id as bid,b.height as bheight,b.weight as bweight,b.xin as bxin,b.gan as bgan,b.qianleixian as bqianleixian,b.description as bdescription, g.id as gid,g.height as gheight,g.weight as gweight,g.xin as gxin,g.gan as ggan,g.zigong as gzigong,g.description as gdescription from user u,boy_healthy b,girl_healthy g where u.id=#{id} and <!--这里的 sex, 指的是前台传入的参数。 这里的写法，见下文。--> <if test='sex=="男"'> u.id=b.userId </if> <if test='sex=="女"'> u.id=g.userId </if> </select> <!-- 嵌套结果 --> <resultMap type="boyBean" id="boyHealthyMapWithResult" extends="userResultMapWithDiscriminator"> <collection property="healthyList" ofType="boyHealthy" javaType="ArrayList"> <id property="id" column="bid"/> <result property="height" column="bheight"/> <result property="weight" column="bweight"/> <result property="xin" column="bxin"/> <result property="gan" column="bgan"/> <result property="qianleixian" column="bqianleixian"/> <result property="description" column="bdescription"/> </collection> </resultMap> <resultMap type="girlBean" id="girlHealtyMapWithResult" extends="userResultMapWithDiscriminator"> <collection property="healthyList" ofType="girlHealthy" javaType="ArrayList"> <id property="id" column="gid"/> <result property="height" column="gheight"/> <result property="weight" column="gweight"/> <result property="xin" column="gxin"/> <result property="gan" column="ggan"/> <result property="zigong" column="gzigong"/> <result property="description" column="gdescription"/> </collection> </resultMap>
测试方法:
@Test public void getByIdWithResultTest(){ SqlSession sqlSession=SqlSessionFactoryUtils.getSession(); UserMapper userMapper=sqlSession.getMapper(UserMapper.class); User user=userMapper.getUserByIdWithResultString(1,"男"); System.out.println("员工信息:"+user); if("男".equals(user.getSex())){ BoyBean boyBean=(BoyBean)user; List<BoyHealthy> boyHList=boyBean.getHealthyList(); boyHList.forEach(n ->System.out.println(n)); }else{ GirlBean girlBean=(GirlBean)user; List<GirlHealthy> girlHList=girlBean.getHealthyList(); girlHList.forEach(n ->System.out.println(n)); } }
如果传入的参数是女性，为2 的话。
User user=userMapper.getUserByIdWithResultString(2,“女”);
会发现，动态 if 语句中的写法是:
<if test='sex=="男"'> u.id=b.userId </if> <if test='sex=="女"'> u.id=g.userId </if>
这是为了区分字符串的。 如果写成 if test=“sex==‘男’” ,那么会把男当成char 类型，会报 数字格式化异常 NumberFormatExeption。
当然，也可以 利用 toString() 进行替换。
<if test="sex eq '男'.toString()"> u.id=b.userId </if> <if test="sex eq '女'.toString()"> u.id=g.userId </if>
也可以利用
"
进行转义。
<if test="sex=="男""> u.id=b.userId </if> <if test="sex=="女""> u.id=g.userId </if>
上面扩充的是一个集合。 当然，通常是扩充一下 bean, 添加一些其余的属性。 如在Bean 中，添加其他属性。
四. Bean扩充 对象中属性。
有的时候，普通的对象是无法正确的封装数据展示的，常常会用bean 继承这个对象，然后扩充 这个对象，添加某些属性，达到数据封装的目的。
如 在BoyBean 和GirlBean 中添加其余的属性， 正常的属性，非集合形式。
在BoyBean 中添加 heightDesc 的属性。
/*关于身高的描述*/ private String heightDesc;
在GirlBean 中添加weightDesc 的属性.
/*关于体重的描述*/ private String weightDesc;
UserMapper.java 中接口:
public User getUserByIdWithResultBeanString(@Param(value="id") int id, @Param(value="sex") String sex);
UserMapper.xml sql语句:
<resultMap type="user" id="userResultMapWithDiscriminatorBean"> <!-- 员工的基本属性。 --> <id property="id" column="id"/> <result property="name" column="name"/> <result property="sex" column="sex"/> <result property="age" column="age"/> <result property="description" column="description"/> <!-- 分类选择 --> <discriminator javaType="string" column="sex"> <!-- 扩充的对象为 boyBean --> <case value="男" resultType="boyBean"> <!-- 继续扩充其他的属性。 --> <result property="heightDesc" column="beanDesc"/> </case> <case value="女" resultType="girlBean"> <result property="weightDesc" column="beanDesc"/> </case> </discriminator> </resultMap> <select id="getUserByIdWithResultBeanString" resultMap="userResultMapWithDiscriminatorBean"> select distinct u.id as id,u.name as name,u.sex as sex,u.age as age,u.description as description, if(u.sex='男','男性身高描述','女性身高描述') as beanDesc from user u,boy_healthy b,girl_healthy g where u.id=#{id} and <if test="sex=="男""> u.id=b.userId </if> <if test="sex=="女""> u.id=g.userId </if> </select>
测试方法:
@Test public void getUserByIdWithResultBeanStringTest(){ SqlSession sqlSession=SqlSessionFactoryUtils.getSession(); UserMapper userMapper=sqlSession.getMapper(UserMapper.class); User user=userMapper.getUserByIdWithResultBeanString(2,"女"); System.out.println("员工信息:"+user); if("男".equals(user.getSex())){ BoyBean boyBean=(BoyBean)user; System.out.println("描述是:"+boyBean.getHeightDesc()); }else{ GirlBean girlBean=(GirlBean)user; System.out.println("描述是:"+girlBean.getWeightDesc()); } }
控制台打印输出:
如果是男性的话:
User user=userMapper.getUserByIdWithResultBeanString(1,"男");
这就是discriminator 的基本用法。
谢谢!!!
