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

by philk :: Rate this Message:

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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