JPA Tutorial - JPA Find By ID Example

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Once we saved an entity to database we can retrieve them back by using the find method from EntityManager.

The following code shows how to use the find method with entity id.

Person emp =  em.find(Person.class, 1L);

Example

The following code is from Person.java.

package com.java2s.common;
import static javax.persistence.FetchType.LAZY;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Lob;
import javax.persistence.Table;

@Entity
@Table(name="EMP")
public class Person {
  @Id
  @Column(name = "EMP_ID")
  private long id;
  
  @Basic
  private String name;
  private String surname;
  
  @Lob 
  @Basic(fetch=LAZY)
  private byte[] picture;
  
  public Person() {}

  public Person(String name, String surname) {
    this.name = name;
    this.surname = surname;
  }
  
  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 byte[] getPicture() {
    return picture;
  }

  public void setPicture(byte[] picture) {
    this.picture = picture;
  }

  @Override
  public String toString() {
    return "Person [id=" + id + ", name=" + name + ", surname=" + surname + "]";
  }
}

The following code is from PersonDaoImpl.java.

package com.java2s.common;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import org.springframework.transaction.annotation.Transactional;

@Transactional
public class PersonDaoImpl {
  public void test(){
    Person p1 = new Person("Tom", "Smith");
    p1.setId(1L);
    p1.setPicture("asdf".getBytes());
    Person p2 = new Person("Jack", "Kook");
    p2.setId(2L);
    p1.setPicture("java2s.com".getBytes());
    
    save(p1);
    save(p2);

    listAll();
    
    Person emp =  em.find(Person.class, 1L);
    if (emp != null) {
      em.remove(emp);
    }
    listAll();
  }
  private void listAll(){
    List<Person> persons = getAll();
    for (Person person : persons) {
      System.out.println(person);
    }

  }
  @PersistenceContext
  private EntityManager em;
  
  
  public Long save(Person person) {
    em.persist(person);
    return person.getId();
  }
  
  public List<Person>getAll() {
    return em.createQuery("SELECT p FROM Person p", Person.class).getResultList();
  }
  
}

The code above generates the following result.

The following is the database dump.

Table Name: EMP
 Row:
    Column Name: EMP_ID,
    Column Type: BIGINT:
    Column Value: 2

    Column Name: NAME,
    Column Type: VARCHAR:
    Column Value: Jack

    Column Name: PICTURE,
    Column Type: BLOB:
    Column Value: null

    Column Name: SURNAME,
    Column Type: VARCHAR:
    Column Value: Kook

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