java - em.persist 似乎不会在 postgreSQL 数据库上保留数据

Question

我有一个简单的 java main，它必须在 PostgreSQL 数据库上写入 bean 数据。我使用实体管理器来保存或更新对象。我使用在 persistence.xml 文件中指定的 hibernate 和 toplink 驱动程序连接。当我调用 em.persist(obj) 时，数据库中没有保存任何内容，我不知道为什么。这是我的简单代码:

private static void importa(FileReader f) throws IOException {

  EntityManagerFactory emf = Persistence
  .createEntityManagerFactory("orpt2");
  EntityManager em = emf.createEntityManager();

dispositivoMedico = new DispositivoMedico();
dispositivoMedico.setCategoria("prova");
dispositivoMedico.setCodice("323");
em.persist(dispositivoMedico);

这是我的 persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<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="orpt2">
   <class>it.ariadne.orpt2.entities.AccessoriScheda</class>
    <class>it.ariadne.orpt2.entities.CampiSchede</class>
  <class>it.ariadne.orpt2.entities.CampiSchedeSalvati</class>
  <class>it.ariadne.orpt2.entities.CampoAggiuntivo</class> 
   <class>it.ariadne.orpt2.entities.Categorie</class>
  <class>it.ariadne.orpt2.entities.CategorieCampi</class>
  <class>it.ariadne.orpt2.entities.CategorieCampiPK</class>
  <class>it.ariadne.orpt2.entities.ClasseCivab</class> 
  <class>it.ariadne.orpt2.entities.DecodificaStato</class>
  <class>it.ariadne.orpt2.entities.DispositivoMedico</class>
   <class>it.ariadne.orpt2.entities.Ente</class>
    <class>it.ariadne.orpt2.entities.FormaNegoziazione</class>
  <class>it.ariadne.orpt2.entities.Fornitore</class> 
  <class>it.ariadne.orpt2.entities.LogSession</class> 
  <class>it.ariadne.orpt2.entities.Modello</class> 
  <class>it.ariadne.orpt2.entities.Periodicita</class>
  <class>it.ariadne.orpt2.entities.Produttore</class>
   <class>it.ariadne.orpt2.entities.Ruolo</class>
  <class>it.ariadne.orpt2.entities.RuoloPK</class>
  <class>it.ariadne.orpt2.entities.RuoloUtente</class> 
  <class>it.ariadne.orpt2.entities.Scheda</class>
  <class>it.ariadne.orpt2.entities.SchedaSalvata</class>
  <class>it.ariadne.orpt2.entities.Tipologia</class> 
   <class>it.ariadne.orpt2.entities.Utente</class>

  <!-- locale 2010--><!-- optsanmatteo_prova300310 -->
   <properties>

   <property name="hibernate.connection.driver_class"
    value="org.postgresql.Driver" />

   <property name="hibernate.connection.url"
    value="jdbc:postgresql://localhost:5432/optsanmatteo_provaHash" />

   <property name="hibernate.connection.password"
    value="s4sh4gr3y" />

   <property name="hibernate.connection.username"
    value="sanmatteo" />

   <property name="hibernate.dialect"
    value="org.hibernate.dialect.PostgreSQLDialect" />


   <property name="toplink.logging.level" value="WARNING" />
   <property name="toplink.jdbc.driver"
    value="org.postgresql.Driver" />

   <property name="toplink.jdbc.url"
    value="jdbc:postgresql://localhost:5432/optsanmatteo_provaHash" />

   <property name="toplink.jdbc.password" value="s4sh4gr3y" />

   <property name="toplink.jdbc.user"
    value="sanmatteo" />
  </properties>

 </persistence-unit>

</persistence>

感谢您的帮助。

马里奥

Answer 1

首先，persist , merge , remove操作不会直接访问数据库，它们会更改内存中对象的状态 - 在持久性上下文(事务)中。当交易为committed , 或者如果持久化上下文是 flushed ，然后将更改写入数据库。

二、persist操作只能在事务内调用，事务外会抛出异常。所以你需要开始交易。

这里是一个修改过的例子:

EntityManagerFactory emf = Persistence.createEntityManagerFactory("orpt2");
EntityManager em = emf.createEntityManager();
em.getTransaction().begin(); // start a transaction

dispositivoMedico = new DispositivoMedico();
dispositivoMedico.setCategoria("prova");
dispositivoMedico.setCodice("323");

em.persist(dispositivoMedico);

em.getTransaction().commit(); // Commit the current resource transaction, writing
                              // any unflushed changes to the database.