We can set if the mapping column can have null value or if the column should have unique value.
@Column(unique=true, nullable=false)
private String name;
The code above sets the name column to be unique and nullable.
The following code is from Person.java.
package com.java2s.common; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.Table; @Entity @Table(name="EMP") public class Person { @Id private long id; @Column(unique=true, nullable=false) 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 App.java.
package com.java2s.common; 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"); dao.test(); context.close(); Helper.checkData(); } }
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); Person p2 = new Person("Jack", "Kook"); p2.setId(2L); save(p1); save(p2); 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 table dump.
Table Name: EMP Row: Column Name: ID, Column Type: BIGINT: Column Value: 1 Column Name: NAME, Column Type: VARCHAR: Column Value: Tom Column Name: SURNAME, Column Type: VARCHAR: Column Value: Smith Row: Column Name: ID, Column Type: BIGINT: Column Value: 2 Column Name: NAME, Column Type: VARCHAR: Column Value: Jack Column Name: SURNAME, Column Type: VARCHAR: Column Value: Kook