No persistence providers available for “transactio

问题:

I'm having this error in my AppEngine project:

javax.persistence.PersistenceException: No persistence providers available for "transactions-optional" after trying the following discovered implementations: org.datanucleus.api.jpa.PersistenceProviderImpl
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:180)
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:70)

jdoconfig.xml

<jdoconfig xmlns="http://java.sun.com/xml/ns/jdo/jdoconfig"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/jdo/jdoconfig http://java.sun.com/xml/ns/jdo/jdoconfig_3_0.xsd">

    <persistence-manager-factory name="transactions-optional">
        <property name="javax.jdo.PersistenceManagerFactoryClass"
            value="org.datanucleus.api.jdo.PersistenceManagerFactoryClass"/>
        <property name="javax.jdo.option.ConnectionURL" value="appengine"/>
        <property name="javax.jdo.option.NontransactionalRead" value="true"/>
        <property name="javax.jdo.option.NontransactionalWrite" value="true"/>
        <property name="javax.jdo.option.RetainValues" value="true"/>
        <property name="datanucleus.appengine.autoCreateDatastoreTxns" value="true"/>
        <property name="datanucleus.appengine.singletonPMFForName" value="true"/>
    </persistence-manager-factory>
</jdoconfig>

Its really weird since in my jdoconfig.xml there is this "transactions-optional"

回答1:

Obviously JPA (which you use to get an EMF) doesn't use "jdoconfig.xml" (which is used by JDO). JPA uses "persistence.xml". Suggest you decide which API you're using before going further