JPA教程 - JPA Transient示例

如果我们不想将属性保存到数据库，我们可以使用@Transient注释标记该字段。

例子

以下代码来自Professor.java。

package cn.w3cschool.common;
import java.util.Locale;import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Transient;
@Entitypublic class Professor {@Idprivate int id;private String name;private long salary;@Transient private String convertedName;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;convertedName = convertName(name);}public long getSalary() {return salary;}public void setSalary(long salary) {this.salary = salary;}public String getConvertedName() {return convertedName;}public String toString() {return "Employee " + " id: " + getId() + " name: " + getName() + " converted name: " + getConvertedName() + " salary: " + getSalary();}protected String convertName(String name) {// Convert to upper case Canadian...return name.toUpperCase(Locale.CANADA);}
}

下面的代码来自PersonDaoImpl.java。

package cn.w3cschool.common;import java.util.List;import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.TypedQuery;import org.springframework.transaction.annotation.Transactional;@Transactional
public class PersonDaoImpl {public void test() {Professor emp = new Professor();emp.setId(1);emp.setName("name");emp.setSalary(12345);em.persist(emp);}@PersistenceContextprivate EntityManager em;
}

下载 Transient.zip

以下是数据库转储。

Table Name: PROFESSORRow:Column Name: ID,Column Type: INTEGER:Column Value: 1Column Name: NAME,Column Type: VARCHAR:Column Value: nameColumn Name: SALARY,Column Type: BIGINT:Column Value: 12345

JPA教程 - JPA ID注释示例

来自JPA的@Id注释用于将Java字段标记为数据库表主键列。

public class Person{
@Id
private long id;
...

上面的代码将来自Person类的id字段作为数据库中的表person中的主键列。

例子

下面的代码来自Person.java。

package cn.w3cschool.common;import javax.persistence.Entity;
import javax.persistence.Id;@Entity
public class Person {@Idprivate 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;}@Overridepublic String toString() {return "Person [id=" + id + ", name=" + name + ", surname=" + surname + "]";}
}

下面的代码来自PersonDaoImpl.java。

package cn.w3cschool.common;import java.util.List;import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;import org.springframework.transaction.annotation.Transactional;@Transactional
public class PersonDaoImpl {@PersistenceContextprivate 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();}}

以下代码来自App.java。

package cn.w3cschool.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();}
}

上面的代码生成以下结果。

以下是数据库表转储。

Table Name: PERSONRow:Column Name: ID,Column Type: BIGINT:Column Value: 1Column Name: NAME,Column Type: VARCHAR:Column Value: XMLColumn Name: SURNAME,Column Type: VARCHAR:Column Value: HTMLRow:Column Name: ID,Column Type: BIGINT:Column Value: 2Column Name: NAME,Column Type: VARCHAR:Column Value: JavaColumn Name: SURNAME,Column Type: VARCHAR:Column Value: SQL