JPA entities and persistence with Hibernate(hbm2ddl.auto)
Assuming that you have your project set up complete, we are proceeding in this tutorial with the demonstration of the JPA entity creation. In this tutorial we will create an entity called Student and will use Hibernate's auto generation property to persist the entity in the database.
int id String firstName String lastName String Standerd
Now click Finish to complete the wizard and generate the code. Once you are through the code will be presented to you with the fields you created and pre generated getters and setters method for the fields. Also there shall be Serializable Interface implemented and auto generated serial version id. initially the fields generated looks like following code snippet.
@Id
private int id;
private String firstName;
private String lastName;
private String standerd;
private static final long serialVersionUID = 1L;
Also we want to make sure that our columns are not null, so we use @NotNull annotation which is a validation constraint to ensure the not null property on the table column, also we want to limit the length of the fields so we are using @Length annotation with property max. This will make sure when the table is generated it has limited length defined for the columns. So after the basic tuning here is how our code looks like.
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private int id;
@NotNull
@Length(max=20)
private String firstName;
@NotNull
@Length(max=20)
private String lastName;
@NotNull
@Length(max=5)
private String standerd;
private static final long serialVersionUID = 1L;
@Entity
@NamedQuery(name="Student.getAll",query="SELECT s FROM Student s")
public class Student implements Serializable {
...
package com.em.jpa.entity;
import java.io.Serializable;
import java.lang.String;
import javax.persistence.*;
import javax.validation.constraints.NotNull;
import org.hibernate.validator.constraints.Length;
/**
* Entity implementation class for Entity: Student
*
*/
@Entity
@NamedQuery(name="Student.getAll",query="SELECT s FROM Student s")
public class Student implements Serializable {
@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private int id;
@NotNull
@Length(max=20)
private String firstName;
@NotNull
@Length(max=20)
private String lastName;
@NotNull
@Length(max=5)
private String standerd;
private static final long serialVersionUID = 1L;
public Student() {
super();
}
public int getId() {
return this.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 getStanderd() {
return standerd;
}
public void setStanderd(String standerd) {
this.standerd = standerd;
}
}
<persistence-unit name="DemoEJB">
<jta-data-source>java:jboss/datasources/school</jta-data-source>
...
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.1" 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">
<persistence-unit name="DemoEJB">
<jta-data-source>java:jboss/datasources/school</jta-data-source>
<properties>
<property name="hibernate.hbm2ddl.auto" value="update"/>
</properties>
</persistence-unit>
</persistence>
Our persistence unit is now ready to work, when you deploy the application you will notice the creation of table named Student in the database and on checking the structure you will find that table has been created in database.
Please feel free to comment if you find some error in the program or there is some problem in the implementation of the program. In the next part we will describe the use of EJB, we are going to divide the EJB part in two subpart, that would be using Local and Remote interface implementation.
