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Re: [eclipselink-dev] Loading multiple persistence.xml files 
Hi Carl,
Is the number of mapping files you get known or constrained? If so, it may be possible to build jar files containing your domain classes and orm.xml files and point to them in the persistence.xml file using <jar-file>.
As for the "classloader trick"... Although I have not heard of it, it is plausible that it might work. If you are in a JavaSE-type deployment, EclipseLink processes the persistence.xml and as long as it is available to System.getResources("META-INF/persistence.xml") when we bootstrap, I can't see why it wouldn't work. There is even some API that allows you to tell us what classloader to use. The only issue I can think of in this type of deployment is that the dynamic weaving we can do for performance might not work.
JavaEE-type deployments would likely depend on what application server you are running since the app-server controls the processing of persistence.xml. 

-Tom

Carl Hall wrote:
That works out fine. Our system pulls in jars that are self contained projects. I don't have a way to know what mapping files are available without querying the classloader. 

e.g.
Sakai ClassLoader sees:
  project1.jar!META-INF/persistence.xml   <-- defines "default" UoW
  project1.jar!META-INF/orm.xml
  project2.jar!META-INF/persistence.xml   <-- also defines "default" UoW
  project2.jar!META-INF/orm.xml
etc.
The classloader "trick" I've seen is to query for all these files then inject into getResources() such that either, on-the-fly, 1) create a persistence.xml that contains a mapping entry for each orm.xml found or 2) merge all orm.xml files into 1 file and return a reference.
On Wed, Dec 17, 2008 at 11:07, Tom Ware <tom.ware@xxxxxxxxxx <mailto:tom.ware@xxxxxxxxxx>> wrote: 

    Hi Carl,

     What issues are you seeing when you specify several orm files
    within the same persistence unit definition in one persistence.xml file?

    e.g.

    <persistence 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
    persistence_1_0.xsd" version="1.0">

       <persistence-unit name="default" transaction-type="RESOURCE_LOCAL">
           <provider>
               org.eclipse.persistence.jpa.PersistenceProvider
           </provider>
<mapping-file>META-INF/advanced-entity-mappings.xml</mapping-file> <mapping-file>META-INF/inheritance-entity-mappings.xml</mapping-file--> <mapping-file>META-INF/inherited-entity-mappings.xml</mapping-file> <mapping-file>META-INF/relationships-entity-mappings.xml</mapping-file> 


    etc....


    -Tom

    Carl Hall wrote:

        Hi, Tom.

        You've nailed it.  Each persistence.xml is trying to create the
        same persistence unit ("default").  Is there a nice way to load
        1 persistence unit from multiple orm.xml files?  I've seen some
        classloader tricks to accomplish this but don't want to head
        down that rabbit hole unless necessary.

        Thanks,
        Carl


        On Wed, Dec 17, 2008 at 10:55, Tom Ware <tom.ware@xxxxxxxxxx
        <mailto:tom.ware@xxxxxxxxxx> <mailto:tom.ware@xxxxxxxxxx
        <mailto:tom.ware@xxxxxxxxxx>>> wrote:

           Hi Carl,

            Are you using separate EntityManagers for each persistence unit?

            An EntityManager represents one persistence unit - when the
           EntityManagerFactory is created, you get it by persistence unit
           name.  Any EntityManager created by that factory will
        represent that
           persistence unit.

            The name of a persistence unit is specified in the
        persistence.xml
           and only one persistence.xml may be used to define a given
           persistence units.  It is an error to have multiple
        persistence.xml
           that define the same persistence unit and the behavior is
        undefined
           - I am not surprised that if you are doing this, you get the last
           one loaded.

            To access different persistence units, create an
        EntityManager for
           each.

           -Tom

           Carl Hall wrote:

               I have a setup where multiple project come into a shared
               classloader.  Each project can have its own model files and
               thusly its own persistence.xml and orm.xml files.  When I
        create
               an EntityManager, I see in the logs that each persistence.xml
               file is found (3) and each orm.xml file loads with the
        expected
               entities.  When I try to query or persist using this
               EntityManager, only the entities from the lastly loaded
               persistence.xml is found.  Am I loading this correctly?  Am I
               trying to access things incorrectly?
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