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From Michael Shea <m...@nitido.com>
Subject Order of commits?
Date Wed, 19 Nov 2008 23:10:32 GMT
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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