In this tutorial, we will learn how to remove an object from a database table using JPA. In this tutorial, we will use the Hibernate framework as a JPA provider.
The Java Persistence API (JPA) is the Java standard for mapping Java objects to a relational database. Mapping Java objects to database tables and vice versa is called Object-relational mapping (ORM).
The Java Persistence API (JPA) is the Java standard for mapping Java objects to a relational database. Mapping Java objects to database tables and vice versa is called Object-relational mapping (ORM).
In JPA the EntityManager is an interface that is associated with a persistence context. It is used to interact with the persistence context. We use remove(Object entity)method to remove a managed Entity.
Let's start implementing this tutorial via creating a simple maven project in Eclipse IDE.
Use How to Create a Simple Maven Project in Eclipse article to create a simple Maven project in Eclipse IDE.
3. Add jar Dependencies to pom.xml
<<project
xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>net.javaguides.hibernate</groupId>
<artifactId>hibernate-tutorial</artifactId>
<version>0.0.1-SNAPSHOT</version>
</parent>
<artifactId>jpa-crud-example</artifactId>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencies>
<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.13</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>5.3.7.Final</version>
</dependency>
</dependencies>
<build>
<sourceDirectory>src/main/java</sourceDirectory>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
</plugins>
</build>
</project>
4. Creating the JPA Entity Class(Persistent class)
Create a Student entity class under net.javaguides.hibernate.entity package as follows.
package net.javaguides.hibernate.entity;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name = "student")
public class Student {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private int id;
@Column(name = "first_name")
private String firstName;
@Column(name = "last_name")
private String lastName;
@Column(name = "email")
private String email;
public Student() {
}
public Student(String firstName, String lastName, String email) {
this.firstName = firstName;
this.lastName = lastName;
this.email = email;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
@Override
public String toString() {
return "Student [id=" + id + ", firstName=" + firstName + ", lastName=" + lastName + ", email=" + email + "]";
}
}
5. JPA remove() Entity
Let's use the EntityManager interface remove() method to remove or delete entity from the database.
package net.javaguides.hibernate; import javax.persistence.EntityManager; import javax.persistence.EntityTransaction; import net.javaguides.hibernate.entity.Student; import net.javaguides.hibernate.util.JPAUtil; /** * JPA example * @author Ramesh Fadatare * */ public class CRUDOperations { public void removeEntity() { EntityManager entityManager = JPAUtil.getEntityManagerFactory().createEntityManager(); entityManager.getTransaction().begin(); Student student = entityManager.find(Student.class, 1); System.out.println("student id :: " + student.getId()); System.out.println("student firstname :: " + student.getFirstName()); System.out.println("student lastname :: " + student.getLastName()); System.out.println("student email :: " + student.getEmail()); entityManager.remove(student); entityManager.getTransaction().commit(); entityManager.close(); } }
6. Create a JPA configuration file
Create an XML file named as persistence.xml under src/main/java/META-INF folder and write the following code in it.
<persistence
xmlns="http://xmlns.jcp.org/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
version="2.1">
<persistence-unit name="PERSISTENCE">
<description> Hibernate JPA Configuration Example</description>
<provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
<class>net.javaguides.hibernate.entity.Student</class>
<properties>
<property name="javax.persistence.jdbc.driver"
value="com.mysql.cj.jdbc.Driver" />
<property name="javax.persistence.jdbc.url"
value="jdbc:mysql://localhost:3306/hibernate_db" />
<property name="javax.persistence.jdbc.user" value="root" />
<property name="javax.persistence.jdbc.password"
value="root" />
<property name="hibernate.show_sql" value="true" />
<property name="hibernate.hbm2ddl.auto" value="create-drop" />
</properties>
</persistence-unit>
</persistence>
7. Create a JPA helper class
Create a helper class to bootstrap a JPA EntityManagerFactory.
package net.javaguides.hibernate.util;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
public class JPAUtil {
private static final String PERSISTENCE_UNIT_NAME = "PERSISTENCE";
private static EntityManagerFactory factory;
public static EntityManagerFactory getEntityManagerFactory() {
if (factory == null) {
factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
}
return factory;
}
public static void shutdown() {
if (factory != null) {
factory.close();
}
}
}
8. Create the main class and run an application
Here is the main class to persist student object using the EntityManager.persist() method.
MainApp.java
package net.javaguides.hibernate;
public class App {
public static void main(String[] args) {
CRUDOperations crudOperations = new CRUDOperations();
crudOperations.removeEntity();
}
}
Learn complete JPA at JPA Tutorial - Java Persistence API
Learn Hibernate ORM Framework at Hibernate Tutorial
References
Hibernate Framework
Java
JPA
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