About Bijoy K J

Website:
bijoy has written 2 articles so far, you can find them below.

The find method in jpa example

We already discussed the fundamentals of JPA earlier. We also discussed the select query in  JPA which returns object(s) which satisfies the mentioned condition  in an earlier chapter. In this chapter we are looking into the find method in JPA which can be used to find a particular object based on   a primary key value specified.

The find method in jpa example

Here Open JPA is using as implementation.The steps in creating an Open JPA project is already discussed in the earlier chapter.We need the same set up here also.The same entity class and persistence.xml is using here also.In this chapter we are searching for a particular Student object using the find() method EntityManager .We are trying to acess an object which is already existing in the table.

Student.java

import java.io.Serializable;
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(name = "Student")
@Table(name = "student")
public class Student implements Serializable {

/**
*
*/
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int id;
private String name;
private String level;

public Student() {

}

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

@Column(name = "name")
public void setName(String name) {
this.name = name;
}

public String getLevel() {
return level;
}

@Column(name = "level")
public void setLevel(String level) {
this.level = level;
}

public String toString() {
return "ID = " + getId() + " ; Name : = " + getName() + " ; Level : = "
+ getLevel();
}

}

persistence.xml

org.apache.openjpa.persistence.PersistenceProviderImpl com.jpa.entity.Student

We already inserted the data in the previous example. We are retrieving a Student object. In this case the primary key is 1. Since Strategy.AUTO is used in the entity , we cannot guarantee the existence of an object with primary key 1. We need to verify the primary key values of existing objects in table and we need to give the appropriate primary key to get a valid object as output.

TransactionSample.java

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import com.jpa.entity.Student;

public class TransactionSample {

public void retrieveObjects() {
EntityManagerFactory entityManagerFactory = Persistence
.createEntityManagerFactory("OpenJPASample");
EntityManager entitymanager = entityManagerFactory
.createEntityManager();
if (null != entitymanager) {
Student student = new Student();
student.setId(1);
Student student1 = entitymanager.find(Student.class, 1);
if (null != student1) {
System.out.println("Retrived object .. " + student1);
} else {
System.out.println("No object found...");
}

}
}

public static void main(String[] args) {
TransactionSample sample = new TransactionSample();
sample.retrieveObjects();
}
}

Output

Run the TransactionSample.java. Based on the primary key value given , the object will be retrieved.

See Related Posts

JPA Overview

JPA Example

Updating a record using JPA

JPA Delete Example

JPQL

JPQL Update Query Example

JPQL Delete Query

Caching

Overview to JPA Caching

Locking in JPA

Locking in JPA

Relational Mappings in JPA

One To One Mapping in JPA

One To Many mapping in JPA

Many To Many Mapping in JPA

Many To One Mapping in JPA