With this example we are going to demonstrate how to delete with a condition in JPA. The Java Persistence API provides Java developers with an object/relational mapping facility for managing relational data in Java applications.
Here, we are using JPA to delete an entity using a condition.
DeleteWithCondition class
In DeleteWithCondition class we create an EntityManagerFactory interface to interact with the entity manager factory for MyPeristenceUnit, that is defined in persistence.xml file. We create an EntityManager, using the createEntityManager() API method. Then, we create new Employee objects. The new objects are written to the database, using the persist(java.lang.Object entity) API method of EntityManager. The getTransaction().begin() and getTransaction().commit() methods are used before and after the EntityManager invokes a method so that a transaction begins and ends. The Employee object can be deleted using the createQuery(String qlString) API method of EntityManager, with an sql String query to delete a specified employee.
package com.javacodegeeks.snippets.enterprise;
import java.util.Date;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;
public class DeleteWithCondition {
public static void main(String[] args) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("MyPersistenceUnit");
EntityManager em = emf.createEntityManager();
// create entities
em.getTransaction().begin();
Employee employee = new Employee();
employee.setName("Jack");
employee.setSurname("Thomson");
employee.setTitle("QA Engineer");
employee.setCreated(new Date());
em.persist(employee);
employee = new Employee();
employee.setName("John");
employee.setSurname("Peterson");
employee.setTitle("Software Engineer");
employee.setCreated(new Date());
em.persist(employee);
employee = new Employee();
employee.setName("Mary");
employee.setSurname("Nicholson");
employee.setTitle("Project Manager");
employee.setCreated(new Date());
em.persist(employee);
em.getTransaction().commit();
// delete with condition
em.getTransaction().begin();
Query query = em.createQuery("DELETE FROM Employee e WHERE title like '%Engineer%'");
long rows = query.executeUpdate();
System.out.println("Rows deleted: " + rows);
em.getTransaction().commit();
em.close();
emf.close();
}
}
Employee Class
The Employee class is an entity class, annotated with the javax.persistence.Entity annotation. It uses the @Id annotation to define its id property, and the @GeneratedValue annotation with strategy set to GenerationType.AUTO so that the id gets auto-generated values.
package com.javacodegeeks.snippets.enterprise;
import java.util.Date;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
@Entity
public class Employee {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private Long id;
private String name;
private String surname;
private String title;
private Date created;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSurname() {
return surname;
}
public void setSurname(String surname) {
this.surname = surname;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public Date getCreated() {
return created;
}
public void setCreated(Date created) {
this.created = created;
}
@Override
public String toString() {
return "Employee [id=" + id + ", name=" + name + ", surname=" + surname
+ ", title=" + title + "]";
}
}
persistence.xml
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0">
<persistence-unit name="MyPersistenceUnit" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<properties>
<property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect" />
<property name="hibernate.hbm2ddl.auto" value="update" />
<property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver" />
<property name="hibernate.connection.username" value="jcg" />
<property name="hibernate.connection.password" value="jcg" />
<property name="hibernate.connection.url" value="jdbc:mysql://localhost/companydb" />
</properties>
</persistence-unit>
</persistence>
Output:
Rows deleted: 2
This was an example of how to delete with a condition in JPA.
