7.1 Hibernate：内置生成器 -- assigned

assigned

是 Hibernate 内置的默认生成器策略，应用程序应该对持久化对象的唯一标识符赋值。

特点：可以跨数据库，人为控制主键生成，建议尽量避免。

1 使用 XML

1.1 持久化类定义：

package hibernate;

import java.util.Date;

public class Person {

private Integer id;

private String account;

private String name;

private Date birth;

public Person() {}

public Person(String account, String name, Date birth) {
this.account = account;
this.name = name;
this.birth = birth;
}

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getAccount() {
return account;
}

public void setAccount(String account) {
this.account = account;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Date getBirth() {
return birth;
}

public void setBirth(Date birth) {
this.birth = birth;
}

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

}

1.2 定义映射：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="hibernate.Person" table="PERSON">
<id name="id" type="int">
<column name="ID" />
<generator class="assigned" />
</id>
<property name="account" type="java.lang.String">
<column name="ACCOUNT" />
</property>
<property name="name" type="java.lang.String">
<column name="NAME" />
</property>
<property name="birth" type="java.util.Date">
<column name="BIRTH" />
</property>
</class>
</hibernate-mapping>

1.3 单元测试：

package hibernate;

import java.util.Date;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.junit.Test;

public class HibernateTest {

@Test
public void test() {
Configuration configuration = new Configuration().configure("hibernate.cfg.xml");
SessionFactory sessionFactory = configuration.buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Person person = new Person("admin", "Nick", new Date(System.currentTimeMillis()));
session.save(person);
transaction.commit();
session.close();
sessionFactory.close();
}

}

单元测试抛出异常

org.hibernate.id.IdentifierGenerationException

，指明保存前必须为此类的唯一标识赋值。

org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned beforeQuery call
4000
ing save(): hibernate.Person
at org.hibernate.id.Assigned.generate(Assigned.java:33)
at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:105)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:192)
at org.hibernate.event.internal.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:38)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:177)
at org.hibernate.event.internal.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:32)
at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:73)
at org.hibernate.internal.SessionImpl.fireSave(SessionImpl.java:689)
at org.hibernate.internal.SessionImpl.save(SessionImpl.java:681)
at org.hibernate.internal.SessionImpl.save(SessionImpl.java:676)
at hibernate.HibernateTest.test(HibernateTest.java:20)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:678)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)

修改单元测试代码，添加对ID的赋值：

@Test
public void test() {
Configuration configuration = new Configuration().configure("hibernate.cfg.xml");
SessionFactory sessionFactory = configuration.buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();
Person person = new Person("admin", "Nick", new Date(System.currentTimeMillis()));
person.setId(999);
session.save(person);
transaction.commit();
session.close();
sessionFactory.close();
}

保存后运行，测试通过，数据库中已经查询到新增数据（测试结果略）

注意：

持久化类定义唯一标识属性的类型设为

java.lang.Integer

，不能设置为原始类型

int

，否则第一次运行单元测试即通过，因为

int

默认初始值为 0，而

java.lang.Integer

必须手动赋值，否则为

null

。

XML 映射文件中

<generator class="assigned" />

可以省略，默认生成器策略即为

assigned

。

2 使用注解（annotation）

使用注解定义持久化类：

package hibernate;

import java.util.Date;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

import org.hibernate.annotations.GenericGenerator;

@Entity
@Table
public class Person {

@Id
@GeneratedValue(generator = "assignedGenerator")
@GenericGenerator(name = "assignedGenerator", strategy = "assigned")
private Integer id;

private String account;

private String name;

private Date birth;

public Person() {}

public Person(String account, String name, Date birth) {
this.account = account;
this.name = name;
this.birth = birth;
}

public Integer getId() {
return id;
}

public void setId(Integer id) {
this.id = id;
}

public String getAccount() {
return account;
}

public void setAccount(String account) {
this.account = accoun
c3dc
t;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public Date getBirth() {
return birth;
}

public void setBirth(Date birth) {
this.birth = birth;
}

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

}

运行【1.3 单元测试】，测试结果相同。

以下注解可以省略：

@GeneratedValue(generator = "assignedGenerator")
@GenericGenerator(name = "assignedGenerator", strategy = "assigned")