The @Id annotation from JPA is for marking a Java field as the database table primary key column.
public class Person{ @Id private long id; ...
The code above mark id field from Person class as the primary key column in table person in database.
The following code is from Person.java.
package com.java2s.common; import javax.persistence.Entity; import javax.persistence.Id; @Entity public class Person { @Id private long id; private String name; private String surname; 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; } @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 { @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 following code is from App.java.
package com.java2s.common; import java.util.List; import org.springframework.context.support.ClassPathXmlApplicationContext; public class App { public static void main(String[] args) { ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext( "applicationContext.xml"); PersonDaoImpl dao = (PersonDaoImpl) context.getBean("personDao"); Person p1 = new Person("XML", "HTML"); p1.setId(1L); Person p2 = new Person("Java", "SQL"); p2.setId(2L); dao.save(p1); dao.save(p2); List<Person> persons = dao.getAll(); for (Person person : persons) { System.out.println(person); } context.close(); Helper.checkData(); } }
The code above generates the following result.
The following is the database table dump.
Table Name: PERSON Row: Column Name: ID, Column Type: BIGINT: Column Value: 1 Column Name: NAME, Column Type: VARCHAR: Column Value: XML Column Name: SURNAME, Column Type: VARCHAR: Column Value: HTML Row: Column Name: ID, Column Type: BIGINT: Column Value: 2 Column Name: NAME, Column Type: VARCHAR: Column Value: Java Column Name: SURNAME, Column Type: VARCHAR: Column Value: SQL