mybatis文件映射之利用延迟加载解决collection分布查询（六）

发布时间：2020-12-14 18:03:05 所属栏目：大数据来源：网络整理

导读：Employee.java public class Employee { private Integer id; String lastName; String gender; String email; Department dept;} Department.java Department { String deptName; private ListEmployee employee;} EmployeeMapperPlus.java interface Emplo

Employee.java

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

Department.java

 Department {
     String deptName;
    private List<Employee> employee;
}

EmployeeMapperPlus.java

interface EmployeeMapperPlus {
    public List<Employee> getEmpsByDeptId(Integer id);
}

EmployeeMapperPlus.xml

    <select id="getEmpsByDeptId" resultType="com.gong.mybatis.bean.Employee">
        select * from tbl_employee where d_id=#{deptId}
    </select>

DepartmentMapper.java

 DepartmentMapper {    
    public Department getDeptByIdStep(Integer id);
}

DepartmentMapper.xml

    resultMap type="com.gong.mybatis.bean.Department" id="MyDeptStep">
        id column="id" property="id"/>
        result ="dept_name"="deptName"collection property="employee" select="com.gong.mybatis.dao.EmployeeMapperPlus.getEmpsByDeptId"
        column>    
        collection>
    resultMap="getDeptByIdStep" resultMap
        select id,dept_name from tbl_department where id=#{id}
    >

同样的在mybatis配置文件中：

    settingssetting name="lazyLoadingEnabled" value="true"="aggressiveLazyLoading"="false"/>
    >

最后进行测试：

package com.gong.mybatis.test;

import java.io.IOException;
 java.io.InputStream;
 java.util.List;
 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.Department;
 com.gong.mybatis.bean.Employee;
 com.gong.mybatis.dao.DepartmentMapper;
 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 test2()  IOException {
        SqlSessionFactory sqlSessionFactory = getSqlSessionFactory();
        SqlSession openSession = sqlSessionFactory.openSession();
        try {
            DepartmentMapper mapper = openSession.getMapper(DepartmentMapper.);
            Department department = mapper.getDeptByIdStep(1);
            System.out.println(department.getDeptName());
            openSession.commit();
        } finally {
            openSession.close();
        }
        
    }

}

首先我们只需要部门的名字：

结果：

DEBUG 01-20 19:35:58,093 ==> Preparing: select id,dept_name from tbl_department where id=? (BaseJdbcLogger.java:145)
DEBUG 01-20 19:35:58,167 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:145)
DEBUG 01-20 19:35:58,299 <== Total: 1 (BaseJdbcLogger.java:145)
开发部

sql语句只发送了一次。

接下来我们需要部门里面员工信息：

添加：

System.out.println(department.getEmployee());

结果：

DEBUG 01-20 19:50:48,861 ==> Preparing: select id,dept_name from tbl_department where id=? (BaseJdbcLogger.java:145)
DEBUG 01-20 19:50:48,948 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:145)
DEBUG 01-20 19:50:49,123 <== Total: 1 (BaseJdbcLogger.java:145)
开发部
DEBUG 01-20 19:50:49,125 ==> Preparing: select * from tbl_employee where d_id=? (BaseJdbcLogger.java:145)
DEBUG 01-20 19:50:49,126 ==> Parameters: 1(Integer) (BaseJdbcLogger.java:145)
DEBUG 01-20 19:50:49,129 <== Total: 2 (BaseJdbcLogger.java:145)
[Employee [id=1,lastName=xiximayou,gender=1,email=xiximayou@qq.com,dept=null],Employee [id=3,lastName=小红,gender=0,email=xiaohong@qq.com,dept=null]]

发送了两条sql语句。

（编辑：李大同）

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