JPA教程 - JPA表唯一約束示例

JPA教程 - JPA表唯一約束示例

我們可以用@Table注釋添加表約束。

下表為名稱列上的Person表添加了唯一約束。

@Entity
@Table(uniqueConstraints=@UniqueConstraint(columnNames="NAME"))
public class Person {

例子

下面的代碼來自PersonDaoImpl.java。

package cn.w3cschool.common;


import java.util.Calendar;
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");
    p1.setId(1L);
    p1.setDob(Calendar.getInstance());
    
    Person p2 = new Person("Jack");
    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();
  }
  
}

下面的代碼來自Person.java。

package cn.w3cschool.common;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;
import javax.persistence.UniqueConstraint;
@Entity
@Table(uniqueConstraints=@UniqueConstraint(columnNames="NAME"))
public class Person {
  @Id
  private long id;
   
  private String name;
  
  @Temporal(TemporalType.DATE)
  private java.util.Calendar dob;
  
  public Person() {}

  public Person(String name) {
    this.name = name;
  }


  public java.util.Calendar getDob() {
    return dob;
  }

  public void setDob(java.util.Calendar dob) {
    this.dob = dob;
  }

  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 toString() {
    return "\n\nID:" + id + "\nName:" + name + "\n\n"+"Dob"+dob;
  }
}

上面的代碼生成以下結(jié)果。

以下是數(shù)據(jù)庫轉(zhuǎn)儲。

Table Name: PERSON
 Row:
    Column Name: ID,
    Column Type: BIGINT:
    Column Value: 1

    Column Name: DOB,
    Column Type: DATE:
    Column Value: 2014-12-29

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

 Row:
    Column Name: ID,
    Column Type: BIGINT:
    Column Value: 2

    Column Name: DOB,
    Column Type: DATE:
    Column Value: null

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