Doing an Update with JPA

Hello,

To do an Update using JPA/Hibernate, would you use the merge method of the EntityManager class?

Could you also write an UPDATE statement and then execute that query somehow to do the update that way instead?

New to JPA so I'm trying to figure out how best to do it.

Thanks,

mike

When using JPA let the EntityManager to manage the entity objects.
EntityManger.merge should be used.

Also calling merge method explicity is not required, this because:

When using Container Managed Persistance context, the lifecycle of entity bean is managed by EM.
That means any changes in the state of entity will be persisted by the EM in DB at the end of transaction even if merge is not called.

Following is the sample program.

import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.PersistenceContext;
import javax.persistence.PersistenceUnit;

import com.example.bo.Product;

@Stateless
public class ProductManagerBean implements ProductManager {
		
	
	@PersistenceContext(unitName="TestPC")
	EntityManager manager;
	
	
	public void save(){
		
		Product p=new Product();
		p.setName("Pen");
		p.setDescription("Reynold Pen");
		p.setPrice(2300.5);
		p.setQuantity(20);
		
		manager.persist(p);
		System.out.println("Saving successfully");
		//p.setQuantity(50);
		
	}
		
	public String  findByPrimaryKey(int id){
			 if(manager.find(Product.class,id)!=null)
				 return ((Product)manager.find(Product.class,id)).toString();
			 else
				 return "Entity does not exist ";
			
	}
	
	
	public String update(int id,String newName){
			Product p=(Product)manager.find(Product.class,id);
			if(p!=null)
			{
				p.setName(newName);
				return "entity updated successfully";
                                   //Note managre.merge method is not called. But Product will be synchronised with the DB
			}
			 else
				 return "Entity does not exist ";
			
	}

public String delete(int id){
		Product p=(Product)manager.find(Product.class,id);
		if(p!=null)
		{
			manager.remove(p);
			return "entity deleted successfully";
		}
		 else
			 return "Entity does not exist ";
	}

}

Vijay Vishwa wrote:When using JPA let the EntityManager to manage the entity objects.
EntityManger.merge should be used.

Also calling merge method explicity is not required, this because:

When using Container Managed Persistance context, the lifecycle of entity bean is managed by EM.
That means any changes in the state of entity will be persisted by the EM in DB at the end of transaction even if merge is not called.

Following is the sample program.

import javax.ejb.Stateless; import javax.persistence.EntityManager; import javax.persistence.EntityManagerFactory; import javax.persistence.Persistence; import javax.persistence.PersistenceContext; import javax.persistence.PersistenceUnit; import com.example.bo.Product; @Stateless public class ProductManagerBean implements ProductManager { @PersistenceContext(unitName="TestPC") EntityManager manager; public void save(){ Product p=new Product(); p.setName("Pen"); p.setDescription("Reynold Pen"); p.setPrice(2300.5); p.setQuantity(20); manager.persist(p); System.out.println("Saving successfully"); //p.setQuantity(50); } public String findByPrimaryKey(int id){ if(manager.find(Product.class,id)!=null) return ((Product)manager.find(Product.class,id)).toString(); else return "Entity does not exist "; } public String update(int id,String newName){ Product p=(Product)manager.find(Product.class,id); if(p!=null) { p.setName(newName); return "entity updated successfully"; //Note managre.merge method is not called. But Product will be synchronised with the DB } else return "Entity does not exist "; } public String delete(int id){ Product p=(Product)manager.find(Product.class,id); if(p!=null) { manager.remove(p); return "entity deleted successfully"; } else return "Entity does not exist "; } }

Vijay,

That's an awesome explanation!!! The code is a perfect example to compliment your explanation and is easy to follow.

I'm going to try this code on Monday.

Thanks again very much for your terrific reply.

mike