Re: Why is FunctionListMap using identity to check values and not equals?

I understand your use case but not your reasoning:

"So when an Update comes in I do an
itemsLookup.put(key, database.load(key))
which naturally throws an exception
because the new Object is not found in the base list."

As I tried to explain, the put-method does not try to find
the *new* value in the base list, so this can't be the cause
of the exception.

For example, let your items list contain object with identity x and key a.
So, itemsLookup.get(a) would return object x.

Then, you receive an update for key a, so you do
itemsLookup.put(a, database.load(a)) where database.load(a) would return
an object with identity y and key a.
The put-method will lookup the object for key a in its internal delegate map
and should find (the old) object x. Object x is then found by identity
in the base items list and replaced by object y.
The put-method can throw an IllegalStateException if it doesn't find the
*old* object in the base list.

But to help further we would have to see more example code and the concrete
exception with stacktrace...

Holger

BTW, I'm refering to GL 1.8.

>
> If I get an item out of a DB two times it has a different identity each time.
> However it is the same object, as defined by the key (Primary key if you
> want so).
>
> What I would like to have GL do for me is help me reacting to CRUD changes
> in the DB.
> I get JMS messages when an item is created, removed or updated in the
> database. I want to reflect this change in my EventList.
> For Create: add the new item
> for update: refresh the item in the eventlist (if not existing, add it)
> for delete: remove the item from my eventlist.
>
> However using identities it is not possible to do. The lookup of items must
> be using the Key.
>
> Hope its clear now :)
>
>
> Holger Brands wrote:
> >
> > Phil,
> >
> > maybe there is a misunderstanding on my side or on your side.
> > In my opinion, FunctionListMap.put(K key, V value) does the following:
> >
> > After checking the key-value-agreement it looks into the delegate map
> > to find the key. If it's not there, it adds the new value to the
> > underlying EventList.
> > If the key is found, the (old) value is retrieved from the delegate map.
> > Then it iterates over the underlying EventList to find the *old* value by
> > identity
> > to replace it with the *new* value. This looks correct to me.
> > The (new) value that is passed into the put-method is *not* used to
> > compare
> > anything here.
> > I think one reason why the old value is searched by identity is,
> > that it's quite possible to have two equal objects with different keys
> > (according
> > to the key-maker function).
> >
> > Hope this helps,
> > Holger
> >
> >>
> >> I have the following situation:
> >> private final EventList<E> items = GlazedLists.threadSafeList(new
> >> BasicEventList<E>());
> >> private final DisposableMap<Key, E> itemsLookup =
> >> GlazedLists.syncEventListToMap(this.items,
> >>    new FunctionList.Function<E, Key>() {
> >>            public Key evaluate(final E sourceValue) {
> >>                    return getKey(sourceValue);
> >>            }
> >>    });
> >>
> >> I get updates from an external database that say which object (by key)
> >> has
> >> changed or was removed.
> >> The removal using the itemsLookup works. However the put() method uses an
> >> Identity compare to find the item to be replaced. This is of course not
> >> working, since I am loading a new Object (different identity but same
> >> key)
> >> from the database every time. The object with the same Key should be
> >> replaced by using the equals method. How could I achieve that?
> >>
> >> So when an Update comes in I do an
> >> itemsLookup.put(key, database.load(key)) which naturally throws an
> >> exception
> >> because the new Object is not found in the base list.
> >>
> >> Thanks,
> >> Phil
> >> --
> >> View this message in context:
> >> http://www.nabble.com/Why-is-FunctionListMap-using-identity-to-check-values-and-not-equals--tp24066192p24066192.html
> >> Sent from the GlazedLists - User mailing list archive at Nabble.com.
> >>
> >>
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> --
> View this message in context: http://www.nabble.com/Why-is-FunctionListMap-using-identity-to-check-values-and-not-equals--tp24066192p24154654.html
> Sent from the GlazedLists - User mailing list archive at Nabble.com.
>
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