mybatis文件映射之关联查询初探（一）

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

代码语言：javascript复制

public class Employee {
    private Integer id;
    private String lastName;
    private String gender;
    private String email;
    Department dept;
}

Department.java

代码语言：javascript复制

public class Department {
    private Integer id;
    private String deptName;
}

（省略了getters和setters以及toString方法）

EmployeeMapper.java

代码语言：javascript复制

    public Employee getEmpAndDept(Integer id);

EmployeeMapper.xml

代码语言：javascript复制

    <resultMap type="com.gong.mybatis.bean.Employee" id="MySimpleMap">
        <id column="id" property="id"/>
        <result column="last_name" property="lastName"/>
        <result column="gender" property="gender"/>
        <result column="email" property="email"/>
        <result column="did" property="dept.id"/>
        <result column="dept_name" property="dept.deptName"/>
    </resultMap>
    <select id="getEmpAndDept" resultMap="MySimpleMap">
        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：

代码语言：javascript复制

package com.gong.mybatis.test;

import java.io.IOException;
import java.io.InputStream;
import java.util.Map;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import com.gong.mybatis.bean.Employee;
import com.gong.mybatis.dao.EmployeeMapperPlus;

public class TestMybatis2 {
    
    public SqlSessionFactory getSqlSessionFactory() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream is = Resources.getResourceAsStream(resource);
        return new SqlSessionFactoryBuilder().build(is);
    }

    @Test
    public void test() throws IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession();
        try {
            EmployeeMapperPlus mapper = openSession.getMapper(EmployeeMapperPlus.class);
            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,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=?; (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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