mybatis文件映射之关联查询初探（一）

概述现在有一数据库mybatis，两张数据表 tbl_department tbl_employee 其中tbl_employee表中的d_id关联tbl_department表中的id字段 Employ

现在有一数据库mybatis，两张数据表

tbl_department

 

tbl_employee

 

其中tbl_employee表中的d_ID关联tbl_department表中的ID字段

Employee.java

public class Employee {    private Integer ID;     String lastname;     String gender;     String email;    Department dept;}

Department.java

 Department {     String deptname;}

（省略了getters和setters以及toString方法）

EmployeeMapper.java

    public Employee getEmpAndDept(Integer ID);

EmployeeMapper.xml

    <resultMap type="com.gong.mybatis.bean.Employee" ID="MySimpleMap">        ID column="ID" property="ID"/>        result ="last_name"="lastname"="gender"="gender"="email"="email"="dID"="dept.ID"="dept_name"="dept.deptname"/>    </resultMap>    select ID="getEmpAndDept" resultMap>        SELECT e.ID,e.last_name,e.gender,e.email,d.dept_name,d.ID dID         FROM tbl_employee e,tbl_department d        WHERE e.d_ID = d.ID and e.ID=#{ID};    select>

说明：可以支持级联属性映射，由于我们在select标签中为tbl_department中的ID取了别名，因此可以直接在resultMap中对dID进行级联映射。

最后进行测试：

package com.gong.mybatis.test;import java.io.IOException; java.io.inputStream; java.util.Map; org.apache.ibatis.io.Resources; org.apache.ibatis.session.sqlSession; org.apache.ibatis.session.sqlSessionFactory; org.apache.ibatis.session.sqlSessionFactoryBuilder; org.junit.Test; com.gong.mybatis.bean.Employee; com.gong.mybatis.dao.EmployeeMapperPlus; TestMybatis2 {        public sqlSessionFactory getsqlSessionFactory() throws IOException {        String resource = "mybatis-config.xml";        inputStream is = Resources.getResourceAsstream(resource);        return new sqlSessionFactoryBuilder().build(is);    }    @Test    voID test()  IOException {        sqlSessionFactory sqlSessionFactory = getsqlSessionFactory();        sqlSession openSession = sqlSessionFactory.openSession();        try {            EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.);            Employee employee = mapper.getEmpAndDept(3);            System.out.println(employee);            System.out.println(employee.getDept());            openSession.commit();        } finally {            openSession.close();        }            }}

输出：

DEBUG 01-20 12:15:43,557 ==> Preparing: SELECT e.ID,d.ID dID FROM tbl_employee e,tbl_department d WHERE e.d_ID = d.ID and e.ID=?; (BaseJdbcLogger.java:145)
DEBUG 01-20 12:15:43,611 ==> Parameters: 3(Integer) (BaseJdbcLogger.java:145)
DEBUG 01-20 12:15:43,652 <== Total: 1 (BaseJdbcLogger.java:145)
Employee [ID=3,lastname=小红,gender=0,email=xiaohong@qq.com,dept=Department [ID=1,deptname=开发部]]
Department [ID=1,deptname=开发部]

说明关联查询是成功的。

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