FW: [Hibernate-devel] Getting Collections to pull data from the c ache

[Urberg, J. <ju...@ve...>]

I always forget to copy these to the list...

I guess I don't understand the whole caching thing then. Let's use the
following example:

I have a loan with a collection of borrowers.  I issue a query to get all
the borrowers for a loan.  Then I issue a query (or a load) to get a loan.  

I would expect the following to happen:

1) the query against Borrower loads the cache in the ClassPersister for the
Borrower
2) the query against Loan causes the borrower collection on the Loan to get
evaluated
3) Hibernate looks in the Borrower's cache to see if there are any Borrower
records that match the Loan.
3a) If there are matching Borrowers, Hibernate builds a real Collection
class filled with matching Borrower's
3b) If there are no matches, Hibernate puts issues a query to get matching
Borrowers (or adds a proxy if it's a lazy collection)

That would also mean I could issue one query that joined loan and borrower
and returned both in the result set (which loads both caches), ignore the
result set, then do a load on the Loan (which builds the loan from the loan
cache and then does steps 2 & 3.

Thoughts?

Regards,
John


-----Original Message-----
From: Gavin_King/Cirrus%CI...@ci...
[mailto:Gavin_King/Cirrus%CI...@ci...]
Sent: Friday, August 02, 2002 8:15 PM
To: hib...@li...
Subject: RE: [Hibernate-devel] Getting Collections to pull data from the
cache




>At the point a collection is loaded from the database, Hibernate should
>disassemble each object in the collection and store that either with the
>collection's owner's cached value or in a cache in the collection's
>CollectionPersistor.
>
>Is that correct?

yes. essentially correct.

After the collection is initialized, the CollectionPersister should
disassemble the collection (ie. turn it into an array of elements or array
of elements and indices). Then any contained objects should also be
disassembled ie.

entities -> an id
components -> property array
subcollections -> an id
mutable types -> a clone

currently this logic is already implemented for you, but in the wrong place
(on ClassPersister):

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
     private Object disassemble(Object object, Type type,
SessionImplementor session) throws HibernateException, SQLException  {
          if ( object==null ) {
               return null;
          }
          else if( type.isPersistentObjectType() ) {
               return session.getID(object);
          }
          else if( type.isComponentType() ) {
               AbstractComponentType ctype = (AbstractComponentType) type;
               Type[] types = ctype.getSubtypes();
               Object[] values = ctype.getValues(object);
               for ( int i=0; i<types.length; i++ ) {
                    values[i] = disassemble( values[i], types[i], session
);
               }
               return values;
          }
          else if ( type.isPersistentCollectionType() ) {
               PersistentCollection pc;
               if ( object instanceof PersistentCollection ) {
                    pc = (PersistentCollection) object;
               }
               else {
                    pc = session.getArrayHolder(object);
               }
               return session.getLoadedID(pc);
          }
          else { // a leaf
               return type.deepCopy(object, session);
          }
     }
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


We should probably move the assemble() / disassemble() methods to the Type
interface. This would be much more object oriented and flexible than the
above (a really perfect example of the worst kind of non-use of
polymorphism - but I had my reasons at the time....)


After disassembly, we would need to keep the disassembled state in either
the owning object's cache entry (but this conflicts a bit with lazy
collection initialization) or a cache owned by the CollectionPersister.



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