Re: TimeStamp LAG in editing context

[Un-cross-posted from multiple groups; following up just to eof list].

At 10:31 AM 3/6/2003 -0300, Ing.Gaston Blanco wrote:
>I´m setting the lag in the editing context to 1 , then i create an EC, 
>fetch an object. Then, from a sql terminal i change it, and when i refetch 
>the changes are not reflected in my object. I believed that if the lag was 
>to small the snapshot would be refreshed, and my object updated, but this 
>didn´t happened.

Well, here's a stab at explaining what's going on. The 'lag' you've set 
refers to seconds (or ms, I forget, but time) _before the creation_ of the 
EOEditingContext. If you've set it to 1 second, that means that EC will 
make sure not to use snapshots OLDER than 1 second BEFORE the EC was 
CREATED.  So changes that occured AFTER the EC was created----these don't 
disturb the EC's commitment to not using snapshots older than 1 second 
before it was created.

Now you could constantly reset the EOEditingContext's fetchTimestamp(). 
Note that the static method is called default timestamp LAG and means that 
each EC, upon creation, will have it's timestamp set to that much time 
earlier. But the instance method that applies to a particular 
EOEditingContext is called setFetchTimestamp(), and takes an NSTimestamp 
point-in-time---it's not a lag, it's an actual point-in-time, and the EC 
will refuse to accept snapshots prior to this point in time.  So you could 
be constantly resetting this fetchTimestamp to be just a few seconds before 
NOW.  I'm not sure what effect this will have---it could be deleterious on 
efficiency, as in-memory EOs are constantly refetched because they're 
snapshots are no good. Alternately, it might not even do what you want: I 
suspect it only effects _fetches_, it won't effect EOs in memory, possibly 
unless you refetch those EOs. But you say you are doing a refetch, so it 
might have the consequences you want.  In fact, this might be a very good 
idea, but I'm not really sure, it makes me a little bit nervous.

Alternately, you always have available to you: setting 
refreshesRefetchedObjects to true on a particular EOFetchSpecification. 
This means, regardless of the timestamp on the EC, when you do this fetch, 
take the fresh values from the db and use them to create a new 
snapshot.  It applies to just that one fetch spec, and the timestamp set on 
the EC doesn't matter at all.

Hope this helps,
--Jonathan


>Any clue?????
>
>thanks
>
>
>Ing. Gaston Blanco
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