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Hibernate EntityManager

By Priya PedamkarPriya Pedamkar

Home » Software Development » Software Development Tutorials » Hibernate Tutorial » Hibernate EntityManager

Hibernate EntityManager

Introduction to Hibernate EntityManager

Hibernate EntityManager or, also called JPA EntityManager has an important aspect of connecting with the database of a program. One of the most expensive transactions is considered to be the Database connection. In terms of java objects, the ORM helps in the representation of database relations. Relational programming and Oops are the two concepts of ORM. A programmer gives a description for the way the objects are to be represented in a database in ORM framework – Hibernate. EntityManager and EntityManagerFactory are teJPA interfaces which Hibernate provides in implementation. Instances are provided for connecting the same database by EntityManagerFactory.

Syntax:

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From EnttityManagerFactory, EntityManager is created.

@PersistenceContext
EntityManager entityManager;

The container is in-charge of transaction in the beginning and the rolling back as well.

How Hibernate EntityManager Annotation Work?

All instances have the same configuration so as to use the same setting defined by implementation default. Many factories of entity managers can be prepared for connection of different datastores. EntityManager JPA is used in accessing databases in any particular application.

Also used in managing persistence instances of entities, find entities by identity primary key, and also query the overall entities.

persist Instance is managed and persisted.
merge The state of a given entity is merged into the current context of persistence.
remove All entity instances are removed.
flush Synchronize database with persistence context.
getReference Entity Not Found exception is thrown. This happens when the instance happens for the first time.
find Ab entity is searched which specifies class and primary key. If found, returned.
setFlushMode For all the objects of persistence context, set flush mode.
lock With the specified lock mode type, lock the entirety instance from the database.
refresh Overwriting and refreshing the state of instances.
clear Persistence context is cleared. All managed entries are detached. Entities that have not been flushed and are changed, are not persisted.
detach Familiar to method clear. Detached objects will be referenced.
contains Looks over if the entity belongs to current persistence context.
getLockMode Current lock mode for instance.
setProperty Entity manager property set.
getProperties Hints and properties with the entity manager.
createNativeQuery Instance query is created for execution of native sql statement language.
createNamedQuery Instance of query is created four Java Persistence execution.
createQuery Instance of query is created for the execution of Java persistence query language statements.
createNamedStoredProcedureQuery Instance is created for execution of a stored procedure in a database.
createStoredProcedureQuery Instance is created for execution of a stored procedure in a database.
joinTransaction Indicates that JTA transaction is active to the entity manager.
isJoinedToTransaction Tells if the entity manager links to the current transaction.
unwrap Access is allowed to the provider specific API and object is returned.
getDelegate Provider object is returned for entity manager and returned.
close Application is closed by the entity manager.
isOpen Look if the entity manager is open.
getTransaction Resource level entity transaction object is returned.
getEntityManagerFactory Entity manager is provided with an entity manager factory.
getCriteriaBuilder For creation of criteria query objects, criteria builder is returned.
getMetamodel Meta model of the persistence unit is accessed with the Meta model interface and is returned.
createEntityGraph A mutable entity graph is returned and used in a dynamically created entity graph.
getEntityGraph A named entity graph is returned.
getFlushMode For all the objects of persistence context, get flush mode.

persist() is a method of EntityManager to manage the entity and persist the database. We should pass entity to save data.

Examples of Hibernate EntityManager

Below are the examples of Hibernate EntityManager:

Example #1

Code:

package com.concretepage;
import javax.persistence.EntityManager;
import com.concretepage.entity.Employee;
public class JPAWriteDemo {
public static void main(String[] args) {
EntityManager entityManager = JPAUtility.getEntityManager();
entityManager.getTransaction().begin();
Employee employee = new Employee(1, "Mahesh", "Varanasi");
entityManager.persist(employee);
entityManager.getTransaction().commit();
entityManager.close();
JPAUtility.close();
System.out.println("Entity saved.");
}
}
package com.democlass_entitymanager;
import javax.persistence.EntityManager;
import com.concretepage.entity.Employee;
public class JPASelectDemo {
public static void main(String[] args) {
EntityManager entityManager = JPAUtility.getEntityManager();
Employee employee1 = entityManager.find(Employee.class, new Integer(1));
System.out.println("Name:"+ emp.getName()+", City:"+ emp.getCity());
JPAUtility.close();
System.out.println("Done");
}

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Output:

Hibernate EntityManager Example 1

Example #2

Code:

package com.democlass_entitymanager;
import javax.persistence.EntityManager;
import com.concretepage.entity.Employee;
public class JPAUpdateDemo {
public static void main(String[] args) {
EntityManager entityManager = JPAUtility.getEntityManager();
Employee emp = entityManager.find(Employee.class, new Integer(1));
System.out.println("Name:"+ emp.getName()+", City:"+ emp.getCity());
entityManager.getTransaction().begin();
emp.setName("Krishna");
emp.setCity("Allahabad");
entityManager.getTransaction().commit();
emp = entityManager.find(Employee.class, new Integer(1));
entityManager.close();
JPAUtility.close();
System.out.println("Name:"+ emp.getName()+", City:"+ emp.getCity());
System.out.println("Entity updated.");
}
}

Output:

Hibernate EntityManager Example 2

Conclusion

In this article, we learned about hibernate entityManager. The types of methods that can be used are studied which are available in the API. They work with persistence context.

Recommended Articles

This is a guide to Hibernate EntityManager. Here we discuss how Hibernate EntityManager Annotation Works and its Examples along with its Code Implementation. You can also go through our other suggested articles to learn more –

  1. Hibernate Versions
  2. Hibernate Annotations
  3. Hibernate Query Language
  4. Hibernate Generator

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