Question

我有两个不同的数据源，我需要两个不同的PersistenceManagerFactory。我总是可以写一个persistence.xml文件。但我希望以编程方式表示它。虽然第二个数据源保持相对不变，但第一个数据源可能通过插件添加了它。这些插件可以带有一个或多个JDO注释类。 persitance.xml在这里不是一个好主意，因为我希望它们在运行时加载。

在Hibernate（以及JPA）中，可以通过创建配置对象并向其添加所有带注释的类来实现。每当我看到一个新的插件被加载时，我总是可以关闭SessionFactory并通过查看@Entity注释从插件中重新加载它。

在DataNucleus / JDO中有类似的方法吗？

我尝试在Google上搜索，但我最终都在DataNucleus site解释如何撰写persitence.xml文件。

Answer 1

Scala中的以下代码演示了如何动态创建PersistenceManager。您只需填充地图并将其传递给JDOHelper#getPersistenceManagerFactory。

private val pu  = props(db.driver, db.url, db.username, db.password)
private val pmf = JDOHelper.getPersistenceManagerFactory(pu.asJava)
private val pm  = pmf.getPersistenceManager.asInstanceOf[JDOPersistenceManager]

下面您可以看到一个示例，说明在H2，MongoDB和PostgreSQL的情况下您可能愿意填充此类地图：

  def props(driver: String, url: String, username: String, password: String): Map[String, Any] =
    driver match {
      case "org.h2.Driver" =>
        Map[String, Any](
          "javax.jdo.option.Mapping"                 -> "h2",
          "datanucleus.schema.autoCreateAll"         -> "true",
          "javax.jdo.PersistenceManagerFactoryClass" -> "org.datanucleus.api.jdo.JDOPersistenceManagerFactory",
          "javax.jdo.option.ConnectionDriverName"    -> driver,
          "javax.jdo.option.ConnectionURL"           -> url,
          "javax.jdo.option.ConnectionUserName"      -> username,
          "javax.jdo.option.ConnectionPassword"      -> password
        )

      case "org.postgresql.Driver" =>
        Map[String, Any](
          "datanucleus.schema.autoCreateAll"         -> "true",
          "javax.jdo.PersistenceManagerFactoryClass" -> "org.datanucleus.api.jdo.JDOPersistenceManagerFactory",
          "javax.jdo.option.ConnectionDriverName"    -> driver,
          "javax.jdo.option.ConnectionURL"           -> url,
          "javax.jdo.option.ConnectionUserName"      -> username,
          "javax.jdo.option.ConnectionPassword"      -> password,
          "javax.jdo.option.RetainValues"            -> "true",
          "javax.jdo.option.RestoreValues"           -> "true",
          "javax.jdo.option.Optimistic"              -> "true",
          "javax.jdo.option.NontransactionalWrite"   -> "false",
          "javax.jdo.option.NontransactionalRead"    -> "true",
          "javax.jdo.option.Multithreaded"           -> "true",
          "javax.jdo.option.IgnoreCache"             -> "false"
        )

      case "mongodb.jdbc.MongoDriver" =>
        Map[String, Any](
          "javax.jdo.option.Mapping"                 -> "mongo",
          "datanucleus.schema.autoCreateAll"         -> "true",
          "javax.jdo.PersistenceManagerFactoryClass" -> "org.datanucleus.api.jdo.JDOPersistenceManagerFactory",
          "javax.jdo.option.ConnectionDriverName"    -> driver,
          "javax.jdo.option.ConnectionURL"           -> url,
          "javax.jdo.option.ConnectionUserName"      -> username,
          "javax.jdo.option.ConnectionPassword"      -> password
        )

      case _ => throw new IllegalArgumentException(s"unknown driver %s".format(driver))
    }

jdo：以编程方式在DataNucleus中创建多个持久性单元

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