Mybatis中的lazyloading

男娘i 2022-06-14 06:48 108阅读 0赞

test代码  
package cn.test.test;

import java.util.List;

import org.apache.ibatis.session.SqlSession;  
import org.junit.Test;

import cn.test.entity.Classes;  
import cn.test.entity.Student;  
import cn.test.utils.MyBatisUtils;

public class TestLoading \{

/**
     * 测试延迟加载
     */
    @Test
    public void testLazy(){
        SqlSession session = MyBatisUtils.openSession();
    
        List<Classes> cs = session.selectList("selectClasses");
    
        MyBatisUtils.close();
    
        // 不访问任何的查询结果.
        // System.out.println("不访问查询结果");
    
        // 访问查询结果中的班级数据
        for(Classes c : cs){
            System.out.println(c.getName());
            for(Student s : c.getStudents()){
                System.out.println(s.getName());
            }
        }
    }

\}  
结果的输出  
时  
:  
08:04:23,854 DEBUG classes.selectClasses:139 - ==> Preparing: select \* from tb\_class  
08:04:23,992 DEBUG classes.selectClasses:139 - ==> Parameters:  
08:04:24,060 TRACE classes.selectClasses:145 - <== Columns: ID, NAME, BEGIN\_TIME, TEACHER\_NAME  
08:04:24,068 TRACE classes.selectClasses:145 - <== Row: 1, 京南, 2016-12-23 00:00:00, 老马  
08:04:24,186 TRACE classes.selectClasses:145 - <== Row: 2, 京北, 2017-02-10 00:00:00, 老高  
08:04:24,187 DEBUG classes.selectClasses:139 - <== Total: 2  
京南  
08:04:24,189 DEBUG student.selectStudentsByClass:139 - ==> Preparing: select id, name, age from tb\_student where class\_id = ?  
08:04:24,189 DEBUG student.selectStudentsByClass:139 - ==> Parameters: 1(BigDecimal)  
08:04:24,191 TRACE student.selectStudentsByClass:145 - <== Columns: ID, NAME, AGE  
08:04:24,191 TRACE student.selectStudentsByClass:145 - <== Row: 1, 小张, 25  
08:04:24,192 TRACE student.selectStudentsByClass:145 - <== Row: 2, 小王, 25  
08:04:24,193 DEBUG student.selectStudentsByClass:139 - <== Total: 2  
小张  
小王  
京北  
08:04:24,193 DEBUG student.selectStudentsByClass:139 - ==> Preparing: select id, name, age from tb\_student where class\_id = ?  
08:04:24,194 DEBUG student.selectStudentsByClass:139 - ==> Parameters: 2(BigDecimal)  
08:04:24,195 TRACE student.selectStudentsByClass:145 - <== Columns: ID, NAME, AGE  
08:04:24,195 TRACE student.selectStudentsByClass:145 - <== Row: 3, 小丽, 25  
08:04:24,197 TRACE student.selectStudentsByClass:145 - <== Row: 4, 小李, 25  
08:04:24,197 DEBUG student.selectStudentsByClass:139 - <== Total: 2  
小丽  
小李

结果的输出:  
时

08:07:46,646 DEBUG classes.selectClasses:139 - ==> Preparing: select \* from tb\_class  
08:07:46,759 DEBUG classes.selectClasses:139 - ==> Parameters:  
08:07:46,852 TRACE classes.selectClasses:145 - <== Columns: ID, NAME, BEGIN\_TIME, TEACHER\_NAME  
08:07:46,864 TRACE classes.selectClasses:145 - <== Row: 1, 京南, 2016-12-23 00:00:00, 老马  
08:07:46,960 TRACE classes.selectClasses:145 - <== Row: 2, 京北, 2017-02-10 00:00:00, 老高  
08:07:46,961 DEBUG classes.selectClasses:139 - <== Total: 2  
08:07:46,962 DEBUG student.selectStudentsByClass:139 - ==> Preparing: select id, name, age from tb\_student where class\_id = ?  
08:07:46,963 DEBUG student.selectStudentsByClass:139 - ==> Parameters: 1(BigDecimal)  
08:07:46,964 TRACE student.selectStudentsByClass:145 - <== Columns: ID, NAME, AGE  
08:07:46,965 TRACE student.selectStudentsByClass:145 - <== Row: 1, 小张, 25  
08:07:46,965 TRACE student.selectStudentsByClass:145 - <== Row: 2, 小王, 25  
08:07:46,966 DEBUG student.selectStudentsByClass:139 - <== Total: 2  
京南  
小张  
小王  
08:07:46,967 DEBUG student.selectStudentsByClass:139 - ==> Preparing: select id, name, age from tb\_student where class\_id = ?  
08:07:46,968 DEBUG student.selectStudentsByClass:139 - ==> Parameters: 2(BigDecimal)  
08:07:46,970 TRACE student.selectStudentsByClass:145 - <== Columns: ID, NAME, AGE  
08:07:46,970 TRACE student.selectStudentsByClass:145 - <== Row: 3, 小丽, 25  
08:07:46,973 TRACE student.selectStudentsByClass:145 - <== Row: 4, 小李, 25  
08:07:46,973 DEBUG student.selectStudentsByClass:139 - <== Total: 2  
京北  
小丽  
小李

核心配置文件:mybatis.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <configuration>
    
        
        <settings>
            
            <setting name="lazyLoadingEnabled" value="true"/>
            
            <setting name="aggressiveLazyLoading" value="false"/>
        </settings>
    
        
        <typeAliases>
            
            
            
            <package name="cn.test.entity"/>
            <package name="java.lang" />
        </typeAliases>
    
        <environments default="development">
            <environment id="development">
                <transactionManager type="JDBC"></transactionManager>
                <dataSource type="POOLED">
                    <property name="driver" value="oracle.jdbc.driver.OracleDriver"/>
                    <property name="url" value="jdbc:oracle:thin:@192.168.1.96:1521:Orcl"/>
                    <property name="username" value="hr"/>
                    <property name="password" value="zrb"/>
                </dataSource>
            </environment>
        </environments>
        <mappers>
            
            
            <mapper resource="cn/test/entity/classes.xml"/>
            <mapper resource="cn/test/entity/student.xml"/>
        </mappers>
    </configuration>