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Hibernate- SELECT Operation

Hibernate - SELECT Operation

We have following methods to perform SELECT Operation in Hibernate

Object	get(Class , Serializable id) 
Object	load(Class, Serializable id) throws ObjectNotFoundException
Parameter get load
Database retrieval It always hits the database It does not hit database
Proxy It returns real object It returns proxy object
Id not found If it does not get the object with id, it returns null If it does get the object with id, it throws ObjectNotFoundException
Use If you are not sure if object with id exists or not, you can use get If you are sure about existence of object, you can use load


Example

public class EmployeeSelect {
	public static void main(String[] args) { 
 
 //1.Load Configuration 
 Configuration cfg = new Configuration();
 cfg.configure("hibernate.cfg.xml");
 
 //2.Create Session
 SessionFactory sf = cfg.buildSessionFactory();
 Session session = sf.openSession();
 
 
 //3.Perform Operations
 Object ob = session.load(EmployeeBo.class, new Integer(1));
 EmployeeBo bo = (EmployeeBo) ob;
 
 System.out.println("SELECTED DATA\n ================");
 System.out.println("EID : "+bo.getEid());
 System.out.println("NAME : "+bo.getName());
 System.out.println("ADDRESS : "+bo.getAddress());
	}
}
------------------------------------------------------
log4j:WARN No appenders could be found for logger org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
Hibernate: select employeebo0_.eid as eid0_0_, employeebo0_.name as name0_0_, employeebo0_.address as address0_0_ from employee employeebo0_ where employeebo0_.eid=?

SELECTED DATA
 ================
EID : 1
NAME : Satya
ADDRESS : VIJYAYAWADA

Get vs load

public class App {
   public static void main(String[] args) {
     Configuration cfg = new Configuration();
     cfg.configure("hibernate.cfg.xml");
     
     SessionFactory factory = cfg.buildSessionFactory();
     Session session = factory.openSession(); 
     
     System.out.println("get : Database retrieval");
     Student bo1 = (Student) session.get(Student.class, new Integer(101));  
     Student bo2 = (Student) session.get(Student.class, new Integer(101));  
      
     System.out.println("get : ID not found.... ");
     Student bo3 = (Student) session.get(Student.class, new Integer(102));
     System.out.println(bo3);
     
     System.out.println("load : Database retrieval");
     Student bo4 = (Student) session.load(Student.class, new Integer(101));  
     Student bo5 = (Student) session.load(Student.class, new Integer(101));  
      
     System.out.println("load : ID not found.... ");
     Student bo6 = (Student) session.load(Student.class, new Integer(102));
     System.out.println(bo6);	
 }

}
---------------------------------------------------------------
get : Database retrieval
Hibernate: select student0_.sno as sno0_0_, student0_.name as name0_0_, student0_.address as address0_0_ from student student0_ where student0_.sno=?

Hibernate: select student0_.sno as sno0_0_, student0_.name as name0_0_, student0_.address as address0_0_ from student student0_ where student0_.sno=?
//Two times it hits the Database

get : ID not found.... 
Hibernate: select student0_.sno as sno0_0_, student0_.name as name0_0_, student0_.address as address0_0_ from student student0_ where student0_.sno=?
null
//No Error , it showing null


load : Database retrieval  
//data with same id already loaded at get() call, it just returns Proxy Object

load : ID not found.... 
Hibernate: select student0_.sno as sno0_0_, student0_.name as name0_0_, student0_.address as address0_0_ from student student0_ where student0_.sno=?
Exception in thread "main" org.hibernate.ObjectNotFoundException: No row with the given identifier exists: [rewrite.Student#102]
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