注入两个@PersistenceContext 之一

Question

考虑拥有两个实体管理器工厂：

<bean id="writeEntityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">...</bean>
<bean id="readOnlyEntityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">...</bean>

然后我想要两个 Bean，我将向其中注入正确的持久性上下文：

<bean id="readOnlyManager" class="..MyDatabaseManager">
<bean id="writeManager" class="..MyDatabaseManager">

bean 看起来像：

public class MyDatabaseManager {

    private javax.persistence.EntityManager em;

    public EntityManager(javax.persistence.EntityManager em) {
        this.em = em;
    }
    ...
}

这显然不行，因为EntityManager不是bean，不能这样注入：

No qualifying bean of type 'javax.persistence.EntityManager' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {}

如何在 bean 中限定正确的 EntityManager？我以前用@PersistenceContext注解，但是这个不能用，需要注入。

如何为此类 Bean 指定 PersistenceContext？

更新：我的问题是如何通过 XML 而不是通过注释注入带有限定符的 PersistenceContext。

Answer 1

persistence.xml（2 个不同实体管理器的 2 个持久性单元，基于您的持久性提供程序，我在这里使用 HibernatePersistence）

<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
   <persistence-unit name="pu1">
      <provider>org.hibernate.ejb.HibernatePersistence</provider>
   </persistence-unit>

   <persistence-unit name="pu2">
      <provider>org.hibernate.ejb.HibernatePersistence</provider>
   </persistence-unit>   
</persistence>

确保使用属性 persistenceUnitName 将持久性单元分配给实体管理器

    <bean id="writeEntityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
            <property name="persistenceXmlLocation" value="classpath: of yout persistence xml" />
            <property name="persistenceUnitName" value="pu1" />  
             .....other configuration of em..  
    </bean>

其他 em 也一样。

现在，使用 MyDatabaseManager 的构造函数注入来注入 EntityManager（使用限定符名称 ex. writeEntityManagerFactory ）

<bean id="mdm" class="MyDatabaseManager">
     <constructor-arg ref = "writeEntityManagerFactory"/>
</bean>

Answer 2

假设您使用 spring 来管理事务我会做的是 2 个不同的事务管理器，然后在我的服务中我会使用最合适的事务管理器，如下所示：

配置部分

@Bean
public LocalContainerEntityManagerFactoryBean writeEntityManagerFactory() {

    LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean();
    //Your configuration here
    return factory;
}

@Bean(name={"writeTx"})
public PlatformTransactionManager writeTransactionManager() {

    JpaTransactionManager txManager = new JpaTransactionManager();
    txManager.setEntityManagerFactory(writeEntityManagerFactory().getObject());
    return txManager;
}

@Bean
public LocalContainerEntityManagerFactoryBean readEntityManagerFactory() {

    LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean();
    //Your configuration here
    return factory;
}

@Bean(name={"readTx"})
public PlatformTransactionManager readTransactionManager() {

    JpaTransactionManager txManager = new JpaTransactionManager();
    txManager.setEntityManagerFactory(readEntityManagerFactory().getObject());
    return txManager;
}

服务层

@Transactional(value="readTx")
public List<Object> read(){
    //Your read code here
}

@Transactional(value="writeTx")
public void write(){
    //Your write code here
}

更新答案 我误解了这个问题。

在你的配置类中你可以定义：

@Bean
    public LocalContainerEntityManagerFactoryBean writeEntityManagerFactory() {

        LocalContainerEntityManagerFactoryBean em  = new LocalContainerEntityManagerFactoryBean();
        em.setDataSource(dataSource());
        em.setPackagesToScan(new String[] { "models" });
        JpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
        em.setJpaVendorAdapter(vendorAdapter);
        em.setJpaProperties(hibProps());
        em.setPersistenceUnitName("writer");
        return em;
    }
    @Bean
    public LocalContainerEntityManagerFactoryBean readEntityManagerFactory() {

        LocalContainerEntityManagerFactoryBean em  = new LocalContainerEntityManagerFactoryBean();
        em.setDataSource(dataSource());
        em.setPackagesToScan(new String[] { "models" });
        JpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
        em.setJpaVendorAdapter(vendorAdapter);
        em.setJpaProperties(hibProps());
        em.setPersistenceUnitName("reader");
        return em;
    }   

请查看PersistenceUnitName 值

然后你可以通过以下方式注入它们：

@PersistenceContext(unitName="writer")
private EntityManager emWriter;

@PersistenceContext(unitName="reader")
private EntityManager emReader;

我刚刚测试过，一切都很好

安杰洛

Answer 3

我想你正在尝试将 entityManager 注入到你的管理器类中

public class MyDatabaseManager {

// where you need to qualify your injection    
private javax.persistence.EntityManager em;

    public EntityManager(javax.persistence.EntityManager em) {
        this.em = em;
    }
    ...
}

这是我项目的工作代码

1. META-INF 文件夹中的 Persistence.xml

    <persistence version="1.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">
        <persistence-unit name="PERSISTENCE_UNIT_T" transaction-type="JTA">
            <provider>foo.bar.PersistenceProvider</provider>
            <jta-data-source>jdbc/DB2</jta-data-source>
   
        </persistence-unit>
   
         <persistence-unit name="PERSISTENCE_UNIT_P" transaction-type="JTA">
            <provider>foo.bar.PersistenceProvider</provider>
            <jta-data-source>jdbc/DB2</jta-data-source>
   
        </persistence-unit> 
    </persistence>
   

2. 限定符接口类SelectDataSource

 @Qualifier
    @Retention(RetentionPolicy.RUNTIME)
    @Target({ ElementType.TYPE, ElementType.FIELD, ElementType.METHOD })
    public @interface SelectDataSource{}

1. EntityManager 类

   公共类 EntityManager {

        public EntityManager() {
        }
   
        @Inject
        @SelectDataSource
        private EntityManager entityManager;
   
        // other entity manager methods
   
    }
   

2. Entity Manager Provider 类提供基于上下文的持久化单元

   公共类 EntityManagerProvider {

        @PersistenceContext(unitName = "PERSISTENCE_UNIT_T")
        private EntityManager entityManagerT;
   
        @PersistenceContext(unitName = "PERSISTENCE_UNIT_P")
        private EntityManager entityManagerP;
   
   
        @Produces
        @SelectDataSource
        EntityManager createEntityManager(InjectionPoint injectionPoint) {
   
            if (System.ENV.equalsIgnoreCase("p")) {
                if (entityManagerP != null) {
   
                    return entityManagerP;
                }
            }
   
            return entityManagerT;
        }
   
    }
   

然后可以使用@Inject

将 EntityManager 类注入到您喜欢的任何地方

下面是一篇关于如何使用上下文依赖注入创建托管实体管理器的好文章 https://www.sitepoint.com/cdi-weld-inject-jpa-hibernate-entity-managers/#usingaproducermethod