Order of commits?

From: Michael Shea (mik..itido.com)
Date: Wed Nov 19 2008 - 18:10:32 EST

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    Hi guys -

    I am wondering if there is any way to tell cayenne what order to commit
    new objects in.

    My issue is basically like this:

    Suppose I have Category objects and Item objects.

    A user can pass in a CategoryDescriptor, which contains a list of
    ItemDescriptors. I want cayenne to generate, from these descriptors, the
    corresponding database-model objects and rows in the database. So I do
    something like this:

    public Category createCategory( CategoryDescriptor categoryDescriptor )
    {
        Context context = ...; // do something to get the context here.
        Category category = context.newObject( Category.class );
        .... // fill in stuff about the category object here.
        for ( ItemDescriptor itemDescriptor :
    categoryDescriptor.getItemDescriptors() )
        {
           Item item = context.newObject( Item.class );
           ... // fill in stuff about the item object here.
        }
        context.commitChanges();
        return Category;
    }

    The problem I am having is that both Category and Item have primary keys
    which are autogenerated by database (I am using MySQL, the ID's are
    generated via AUTO_INCREMENT columns). It looks like cayenne is
    attempting to create the Item objects before creating the Category
    object, and then it's giving me a commit exception like this:

    org.apache.cayenne.CayenneRuntimeException: [v.3.0M4 May 18 2008
    16:32:02] Commit Exception
        at
    org.apache.cayenne.access.DataContext.flushToParent(DataContext.java:1192)
        at
    org.apache.cayenne.access.DataContext.commitChanges(DataContext.java:1066)
        at com.nitido.rss.RSSNugget.createCategory(RSSNugget.java:294)
        ...
    Caused by: com.mysql.jdbc.exceptions.MySQLSyntaxErrorException: Table
    'rss.AUTO_PK_SUPPORT' doesn't exist
        at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1026)
       ...

    It looks like, since the ID on the Item is null and the Category object
    hasn't been initialized yet, Cayenne is trying to generate an ID for the
    row. I don't see any other INSERT commands from the logger after I call
    context.commitChanges(), so the attempt to insert a row for the Item
    object looks to be the first thing that it's trying to do.

    So, my questions are:
    1. Is this normal? Or does this sound like it could be a problem caused
    by me screwing up the mapping.xml?
    3. Is it a good idea to work around this by using either AUTO_PK_SUPPORT
    or a custom database sequence, and forget about the AUTO_INCREMENT
    feature? I have control over the database schema, so I could do this
    instead. Alternately, I could just generate my own ID's without using
    cayenne, but I'd rather not.
    4. Is it normal to do this by committing the Category objects before
    attempting to create Item objects related to them? That seems somewhat
    hacky to me, though.

    BTW, I'm using Cayenne 3.0M4.

    Thanks!

    Shea.

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