Mybaits（9）MyBatis级联-2
一、鉴别器和一对多级联
1.完善体检表，分为男雇员体检和女雇员体检表
（1）持久层dao编写
package com.xhbjava.dao; import com.xhbjava.domain.MaleHealthForm; /** * 男性体检表 * @author Mr.wang *@date 2020年2月27日 */ public interface IMaleHealthFormDao { public MaleHealthForm getMaleHealthForm(Long empId); }
package com.xhbjava.dao; import com.xhbjava.domain.FemaleHealthForm; /** * 女体检表 * @author Mr.wang *@date 2020年2月27日 */ public interface IFemaleHealthFormDao { public FemaleHealthForm getFemaleHealthForm(Long empId); }
package com.xhbjava.dao; import com.xhbjava.domain.Employee; /** * 雇员接口 * @author Mr.wang *@date 2020年2月27日 */ public interface IEmployeeDao { public Employee getEmployee(Long id); }
（2）持久层对于的mapper文件编写
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.xhbjava.dao.IMaleHealthFormDao"> <!-- 查询任务 --> <select id="getMaleHealthForm" parameterType="Long" resultType="com.xhbjava.domain.MaleHealthForm"> select id, heart, liver, spleen, lung, kidney, prostate, note from t_male_health_form where emp_id = #{id} </select> </mapper>
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.xhbjava.dao.IFemaleHealthFormDao"> <!-- 查询任务 --> <select id="getFemaleHealthForm" parameterType="Long" resultType="com.xhbjava.domain.FemaleHealthForm"> select id, heart, liver, spleen, lung, kidney, uterus, note from t_female_health_form where emp_id = #{id} </select> </mapper>
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.xhbjava.dao.IEmployeeDao"> <resultMap type="com.xhbjava.domain.Employee" id="employee"> <id column="id" property="id" /> <result column="real_name" property="realName" /> <result column="sex" property="sex" typeHandler="com.xhbjava.typeHandler.SexTypeHandler" /> <result column="birthday" property="birthday" /> <result column="mobile" property="mobile" /> <result column="email" property="email" /> <result column="position" property="position" /> <result column="note" property="note" /> <association property="workcard" column="id" select="com.xhbjava.dao.IWorkCardDao.getWorkCard" /> <collection property="employeeTaskList" column="id" select="com.xhbjava.dao.IEmployeeTaskDao.getEmployeeTaskByEmpId" /> <discriminator javaType="long" column="sex"> <case value="1" resultMap="femaleHealthFormDao"></case> <case value="2" resultMap="maleHealthFormDao"></case> </discriminator> </resultMap> <resultMap type="com.xhbjava.domain.FemaleEmployee" id="femaleHealthFormDao" extends="employee"> <association property="femaleHealthForm" column="id" select="com.xhbjava.dao.IFemaleHealthFormDao.getFemaleHealthForm" /> </resultMap> <resultMap type="com.xhbjava.domain.MaleEmployee" id="maleHealthFormDao" extends="employee"> <association property="maleHealthForm" column="id" select="com.xhbjava.dao.IMaleHealthFormDao.getMaleHealthForm" /> </resultMap> <select id="getEmployee" parameterType="long" resultMap="employee"> select id,rea_name,as realName,sex,birthday,mobile,email,position,note from t_employee where id = #{id} </select> </mapper>
我们来分析下IEmployeeDao.xml:
association:对工牌进行一对一级联，我们在前面分析过。
collection：一对多级联，select元素指向sql，通过column制定的sql字段作为参数进行传递，然后将结果返给雇员属性employeeTaskList。
discriminator：鉴别器，属性column代表使用哪个字段继续鉴别，这里是sex，子元素case用来进行区分，类似Java的switch...case...语句。resultMap属性表示用哪个ResultMap去映射，例如sex=1，则使用
femaleHealthFormDao进行映射。
对于雇员体检表id为employee的resultMap，通过femaleHealthFormDao和maleHealthFormDao通过extends元素继承。从而可以通过assocation元素去执行关联的字段和sql。
（3）编写测试类进测试
@Test public void getEmployeeTaskByEmpId() { Logger logger = Logger.getLogger(MybatisJunitTest.class); Employee employee = employeeDao.getEmployee(1l); System.out.println("===="+employee.getBirthday()); logger.info(employee.getBirthday()); }
2020-02-27 16:34:33,577 0 [ main] DEBUG ache.ibatis.logging.LogFactory - Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
2020-02-27 16:34:34,204 627 [ main] DEBUG source.pooled.PooledDataSource - PooledDataSource forcefully closed/removed all connections.
2020-02-27 16:34:34,205 628 [ main] DEBUG source.pooled.PooledDataSource - PooledDataSource forcefully closed/removed all connections.
2020-02-27 16:34:34,205 628 [ main] DEBUG source.pooled.PooledDataSource - PooledDataSource forcefully closed/removed all connections.
2020-02-27 16:34:34,206 629 [ main] DEBUG source.pooled.PooledDataSource - PooledDataSource forcefully closed/removed all connections.
2020-02-27 16:34:34,222 645 [ main] DEBUG org.apache.ibatis.io.VFS - Class not found: org.jboss.vfs.VFS
2020-02-27 16:34:34,222 645 [ main] DEBUG org.apache.ibatis.io.JBoss6VFS - JBoss 6 VFS API is not available in this environment.
2020-02-27 16:34:34,224 647 [ main] DEBUG org.apache.ibatis.io.VFS - Class not found: org.jboss.vfs.VirtualFile
2020-02-27 16:34:34,225 648 [ main] DEBUG org.apache.ibatis.io.VFS - VFS implementation org.apache.ibatis.io.JBoss6VFS is not valid in this environment.
2020-02-27 16:34:34,227 650 [ main] DEBUG org.apache.ibatis.io.VFS - Using VFS adapter org.apache.ibatis.io.DefaultVFS
2020-02-27 16:34:34,229 652 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Find JAR URL: file:/F:/my_project/Mybatis06/target/classes/com/xhbjava/dao
2020-02-27 16:34:34,230 653 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Not a JAR: file:/F:/my_project/Mybatis06/target/classes/com/xhbjava/dao
2020-02-27 16:34:34,391 814 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: IEmployeeDao.class
2020-02-27 16:34:34,393 816 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: IEmployeeDao.xml
2020-02-27 16:34:34,394 817 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: IEmployeeTaskDao.class
2020-02-27 16:34:34,395 818 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: IEmployeeTaskDao.xml
2020-02-27 16:34:34,396 819 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: IEmployeeTaskDao1.xml
2020-02-27 16:34:34,397 820 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: IFemaleHealthFormDao.class
2020-02-27 16:34:34,398 821 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: IFemaleHealthFormDao.xml
2020-02-27 16:34:34,399 822 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: IMaleHealthFormDao.class
2020-02-27 16:34:34,400 823 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: IMaleHealthFormDao.xml
2020-02-27 16:34:34,401 824 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: ITaskDao.class
2020-02-27 16:34:34,402 825 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: ITaskDao.xml
2020-02-27 16:34:34,403 826 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: IWorkCardDao.class
2020-02-27 16:34:34,404 827 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: IWorkCardDao.xml
2020-02-27 16:34:34,405 828 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Listing file:/F:/my_project/Mybatis06/target/classes/com/xhbjava/dao
2020-02-27 16:34:34,407 830 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Find JAR URL: file:/F:/my_project/Mybatis06/target/classes/com/xhbjava/dao/IEmployeeDao.class
2020-02-27 16:34:34,408 831 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Not a JAR: file:/F:/my_project/Mybatis06/target/classes/com/xhbjava/dao/IEmployeeDao.class
2020-02-27 16:34:34,411 834 [ main] DEBUG rg.apache.ibatis.io.DefaultVFS - Reader entry: ����
从日志中我们可以看到所有级联都成功了，但是也引发了性能问题，这就是N+1问题。
