相对持久性单元注入？

Question

我有一个包含多个持久性单元定义文件的 Persistence.xml。

我想根据进入系统的用户注入单元EntityManager对象。

是否可以？

@PersistenceContext (unitName = myUnit)

在这种使用中，我收到警告：“属性值必须是常量”

应用程序框架：JSF 2.1 & Spring 3.0.2

持久层：JPA

Answer 1

可以使用CDI吗？您可以编写一个小类，注入所有不同的上下文，然后通过执行一些逻辑的生产者方法将它们提供给您的类。就像这样：

public class PersistenceContext {
    @PersistenceContext(unitName="myUnit") private EntityManager myEm;
    @PersistenceContext(unitName="yourUnit") private EntityManager yourEm;

    @Produces
    public EntityManager getEntityManager(InjectionPoint ip) {
        if (USER IS ME) {
            return myEm;
        }
        else if (USER IS YOU) {
            return yourEm;
        }
        else {
            NOW PANIC AND FREAK OUT
        }
    }
}

然后你可以像这样编写类：

public class FeedReamer {
    @Inject private EntityManager em;
}

一切都会神奇地发生（可能？）。

如果您不想硬编码类中持久性单元的名称，那么您可以显式获取实体管理器工厂，而不是依赖注入：

    @Produces
    public EntityManager getEntityManager(InjectionPoint ip) {
        String persistenceUnitName = somehowDeterminePersistenceUnitName();
        EntityManagerFactory emf = Persistence.createEntityManagerFactory(persistenceUnitName);
        return emf.createEntityManager();
    }

但是，尽管此方法可以在 J2SE 应用程序中工作，< a href="http://docs.oracle.com/javaee/6/api/javax/persistence/Persistence.html#createEntityManagerFactory%28java.lang.String%29" rel="nofollow">Persistence.createEntityManagerFactory 不保证在 J2EE 中工作。规范中的脚注 42（至少是 EJB 3.0 持久性规范）说：

Java EE 容器可能支持使用这些 Java SE 引导 API；但是，不需要支持此类使用。

此外，我相信创建一个新的 EntityManagerFactory 可能会非常慢；您可能会发现需要缓存查找结果。我相信长时间持有 EntityManagerFactory 并从多个线程访问它应该是安全的（但我不确定）。

Answer 2

正如错误消息所示，Java 注释属性必须是常量值，而不是对变量的引用。这是 Java 语言的限制，而不是 JPA 的限制。您需要找到一种不同的方式来完成您想做的事情。

Answer 3

正如另一篇文章中提到的，注释属性必须是常量。

另一种方法可能是以编程方式获取 EntityManager 实例：

Persistence.getEntityManagerFactory().getEntityManager(persistenceUnitName);

您可以根据自己的条件实现分配持久性单元名称所需的逻辑。显然，这具有与持久性不再由容器管理这一事实相关的所有缺点。

Answer 4

我达成了解决方案。我是春天的新学习者。肯定有更好的解决方案，但我仍然想分享解决方案。

applicationContext.xml

<context:component-scan base-package="com.hakdogan.hakdoganjsfspring"/ 

<tx:annotation-driven transaction-manager="transactionManagerConstant"/ 

<tx:annotation-driven transaction-manager="transactionManagerRelative"/ 

<bean id="odev" class="com.hakdogan.hakdoganjsfspring.entity.Nesne"  / 

<bean id="transactionManagerConstant" 
class="org.springframework.orm.jpa.JpaTransactionManager"> 
    <property name="entityManagerFactory" ref="constant"/> 
    <property name="jpaDialect" ref="jpaDialect" /> 
</bean> 
<bean id="transactionManagerRelative" 
class="org.springframework.orm.jpa.JpaTransactionManager"> 
    <property name="entityManagerFactory" ref="relative"/> 
    <property name="jpaDialect" ref="jpaDialect" /> 
</bean> 
<bean id="jpaDialect" 
class="com.hakdogan.hakdoganjsfspring.util.HibernateExtendedJpaDialect" / 

<bean id="persistenceUnitManager" 
class="org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitMa nager"> 
<property name="persistenceXmlLocations"> 
  <list> 
      <value>classpath*:META-INF/persistence.xml</value> 
      <value>classpath*:META-INF/hk.xml</value> 
  </list> 
</property> 
</bean> 
<bean id="constant" 
class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"> 
<property name="persistenceUnitManager" 
ref="persistenceUnitManager" /> 
<property name="persistenceUnitName" value="JSFSpring" /> 
</bean> 
<bean id="relative" 
class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"> 
<property name="persistenceUnitManager" 
ref="persistenceUnitManager" /> 
</bean> 
<bean id="persistenceManager" 
class="com.hakdogan.hakdoganjsfspring.util.PersistenceManager"/> 
</beans>

PersistenceManager.java

public class PersistenceManager { 
   private LocalContainerEntityManagerFactoryBean persistence; 
   public LocalContainerEntityManagerFactoryBean getPersistence() { 
    return persistence; 
   } 

   @Autowired 
   @Qualifier("relative") 
   public void setPersistence(LocalContainerEntityManagerFactoryBean 
persistence) { 
    this.persistence = persistence; 
   } 
}

PersistDAO.java

@Component("persistDAO") 
@Scope("session") 
public class PersistDAO { 
   @PersistenceContext(unitName="JSFSpring") 
   private EntityManager em; 

   @Autowired 
   private PersistenceManager persistenceManager; 

   @Autowired 
   private Nesne nesne; 

   private List<Odev> kayitListesi; 
   private List<Event> eventListesi; 
   private String myUnit = "hakdogan"; 

   public Nesne getNesne() { 
     return nesne; 
   } 

   public void setNesne(Nesne nesne) { 
     this.nesne = nesne; 
   } 

   @Transactional(isolation = Isolation.SERIALIZABLE, propagation = 
    Propagation.REQUIRED) 
   public String kaydet(){ 
      em.persist(nesne); 
      return "/liste.xhtml"; 
   } 

   @Transactional(propagation = Propagation.REQUIRED, readOnly=true) 
   public List<Odev> getKayitListesi() { 
      return kayitListesi = (List<Odev>) 
      em.createNamedQuery("Odev.findAll").getResultList(); 
   } 

   @Transactional(readOnly=true) 
   public List<Event> getEventListesi() { 
      persistenceManager.getPersistence().setPersistenceUnitName(myUnit); 
      EntityManager emt =        persistenceManager.getPersistence().getNativeEntityManagerFactory().createEntityManager(); 
    return eventListesi = (List<Event>) 
    emt.createNamedQuery("Event.findAll").getResultList(); 
   } 
} 

Answer 5

我的解决方案不是解决方案:)

applicationContext.xml:

<context:component-scan base-package="com.hakdogan.hakdoganjsfspring"/>
<context:annotation-config />
<tx:annotation-driven transaction-manager="transactionManagerConstant"/>
<tx:annotation-driven transaction-manager="transactionManagerRelative"/>

<bean id="jpaDialect" class="com.hakdogan.hakdoganjsfspring.util.HibernateExtendedJpaDialect" />
<bean id="transactionManagerConstant" class="org.springframework.orm.jpa.JpaTransactionManager">
    <property name="entityManagerFactory" ref="constant"/>
    <property name="jpaDialect" ref="jpaDialect" />
</bean>

<bean id="transactionManagerRelative" class="org.springframework.orm.jpa.JpaTransactionManager">
    <property name="entityManagerFactory" ref="relative"/>
    <property name="jpaDialect" ref="jpaDialect" />
</bean>

<bean id="constant" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
   <property name="persistenceUnitManager" ref="persistenceUnitManager" />
   <property name="persistenceUnitName" value="JSFSpring" />
</bean>

<bean id="relative" class="org.springframework.orm.jpa.LocalEntityManagerFactoryBean">
   <property name="jpaVendorAdapter" ref="jpaVendorAdapter"/>
   <property name="persistenceUnitName" value="hakdogan" />
</bean>

<bean id="jpaVendorAdapter" class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
   <property name="database" value="MYSQL"/>
   <property name="showSql" value="true"/>
   <property name="generateDdl" value="false"/>
   <property name="databasePlatform" value="org.hibernate.dialect.MySQL5InnoDBDialect"/>
</bean>

<bean id="persistenceUnitManager" class="org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager">
  <property name="persistenceXmlLocations">
   <list>
      <value>classpath*:META-INF/persistence.xml</value>
   </list>
  </property>
</bean>

<bean id="persistenceManager" class="com.hakdogan.hakdoganjsfspring.util.PersistenceManager"/>
<bean id="odev" class="com.hakdogan.hakdoganjsfspring.entity.Odev" scope="prototype" />

</beans>

PersistenceManager.java:

public class PersistenceManager {


@Autowired
private LocalEntityManagerFactoryBean persistence;
private PersistenceProvider provider;

 public EntityManager getBaglam(String unitName){
    if(null == provider)
        provider = persistence.getPersistenceProvider();

    if(!unitName.equals(persistence.getPersistenceUnitName()))
        persistence.setPersistenceUnitName(unitName);

    return provider.createEntityManagerFactory(unitName, null).createEntityManager();
 }
}

PersistDAO.java:

@Component("persistDAO")
@Scope("session")
public class PersistDAO {

   @PersistenceContext(unitName="JSFSpring")
   private EntityManager em;


@Autowired
private PersistenceManager persistenceManager;

private List<Odev> kayitListesi;
private List<Event> eventListesi;
private List<Musteriler> musteriListesi;    

private String myUnit = "hakdogan";


@Transactional(propagation = Propagation.REQUIRED, readOnly=true)
public List<Odev> getKayitListesi() {
    return kayitListesi = (List<Odev>) em.createNamedQuery("Odev.findAll").getResultList();
}

@Transactional(isolation = Isolation.SERIALIZABLE, propagation = Propagation.REQUIRED)
public List<Event> getEventListesi() {
    return persistenceManager.getBaglam(myUnit).createQuery("SELECT e FROM Event e").getResultList();
}

@Transactional(isolation = Isolation.SERIALIZABLE, propagation = Propagation.REQUIRED)
public List<Musteriler> getMusteriListesi() {
    return persistenceManager.getBaglam("musteri").createNamedQuery("Musteriler.findAll").getResultList();
}
}

没有 LocalEntityManagerFactoryBean persistenceUnitManager 等属性。因此，我无法设置单位名称。

代价就是创建EntityManagerFactory 的发生。试图减慢项目进度。

我正在寻找春季有效的解决方案。

谢谢。