7.1 Hibernate：內置生成器 – assigned

assigned 是 Hibernate 內置的默認生成器策略，應用程序應該對持久化對象的惟一標識符賦值。

特色：能夠跨數據庫，人爲控制主鍵生成，建議儘可能避免。

1 使用 XML

1.1 持久化類定義：

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 定義映射：

<?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 單元測試：

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();
    }

}

單元測試拋出異常 org.hibernate.id.IdentifierGenerationException，提示保存前必須爲此類的惟一標識賦值。

org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned beforeQuery calling 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)

1.4 修改單元測試代碼，添加對ID的賦值：

@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();
}

保存後運行，測試經過，數據庫中已經查詢到新增數據（測試結果略） 。

注意：

• 持久化類定義惟一標識屬性的類型設爲 java.lang.Integer，不能設置爲原始類型 int，不然第一次運行單元測試即經過，由於 int 默認初始值爲 0，而 java.lang.Integer 必須手動賦值，不然爲 null。
• XML 映射文件中 <generator class="assigned" /> 能夠省略，默認生成器策略即爲 assigned。

2 使用註解（annotation）

使用註解定義持久化類：

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 = 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 + "]";
    }

}

運行【1.3 單元測試】，測試結果相同。

如下註解能夠省略：

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