Mybatis如何实现延迟加载及缓存

2023-07-14 07:12:03 130

一、延迟加载

1、在mybatis.xml配置文件中，开启延迟加载

2、配置mapper文件

1、一对一

*一方









select*fromstudentwhereid=#{id}

*另一方


select*fromgradewhereid=#{id}

*测试

Studentstudent=smapper.selectStudentGradeById(4);
System.out.println(student);
//student.hashCode();
System.out.println(student.getGrade());

2、一对多

*一方







select*fromgradewhereid=#{id}

*多方


select*fromstudentwheregrade_id=#{grade_id}

*测试

Gradegrade=gmapper.selectById(1);
System.out.println(grade);
//student.hashCode();
System.out.println(grade.getStudents());

二、缓存

1、一级缓存

1、概念

一级缓存是SqlSession范围的缓存，当调用SqlSession的修改，添加，删除，commit()，close()等方法时，就会清空一级缓存。

2、测试

//Studentstudent1=smapper.selectStudentGradeById(1);
//Studentstudent2=smapper.selectStudentGradeById(1);
//System.out.println(student1==student2);//true
//********************************
Studentstudent1=smapper.selectStudentGradeById(1);
Studentstudent=newStudent();
student.setName("杜兰特");
student.setAge(28);
student.setSex(1);
smapper.insertStudent(student);
Studentstudent2=smapper.selectStudentGradeById(1);
System.out.println(student1==student2);//false

2、二级缓存

1、开启二级缓存

1、对象需要实现Serializable接口

2、在mybatis.xml配置文件中，开启二级缓存

3、配置mapper文件

select*fromstudentwhereid=#{id}

2、测试

SqlSessionsqlSession1=sqlSessionFactory.openSession();
StudentMappermapper1=sqlSession1.getMapper(StudentMapper.class);
Studentstudent1=mapper1.selectStudentGradeById(1);
sqlSession1.close();
SqlSessionsqlSession2=sqlSessionFactory.openSession();
StudentMappermapper2=sqlSession2.getMapper(StudentMapper.class);
Studentstudent2=mapper2.selectStudentGradeById(1);
sqlSession2.close();
//只查询了一次数据库。二级缓存存储的是数据，并不是对象
System.out.println(student1==student2);//false

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Mybatis如何实现延迟加载及缓存

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