Uhm, *something like* this, I am not sure this is correct. "RETURN
RESULTS" is OpenBase specific I think, I don't really know the
standard keyword for limiting the number of returned results.
You don't know the standard keyword because there is no "standard"
keyword for limiting results. This is one of those parts of SQL that
is vendor specific. You are correct that "RETURN RESULTS 10" works
in OpenBase. In MySQL "LIMIT 10" would be the syntax. Other vendors
may have even different syntax.
-------------------------
Now, understanding that there will be different "camps" of thinking
on this, here is an alternative: Your query could get much simpler,
and way more efficient, if you cache the average review value in your
Item table. This would allow you to write your raw SQL against a
single database table. This could drastically improve the
performance of your query. The downside is that you must ensure that
your model keeps this value up-to-date with any changes in your
reviews. This is actually a fairly common design pattern that,
slightly, breaks the Don't Repeat Yourself (DRY) principal in favor
of performance. Anytime you can avoid having to join tables will
make your queries much more efficient.
Just a thought, but if it were my code I'd seriously consider this
alternative.
On May 7, 2007, at 1:20 PM, Florijan Stamenkovic wrote:
Hi Drew,
I have two objects: Item and a to-many child, review.
Review has an attribute called rating.
I'm trying to use a fetchspec (which appears to be an
impossibility) that returns the top 10 reviewed items. Basically,
I'd like to sort by [EMAIL PROTECTED] and have only 10 items
returned.
Is there a way to do this in EOModeler?
AFAIK, the only way you could do this in EOModeler is to use raw
SQL and modify your select statement to do the appropriate sorting
and result number limiting. Careful though, your SQL most likely
then becomes vendor specific, and your fetch specification will not
update if you make changes in your entity.
If not, I can return *all* item objects, sort by
[EMAIL PROTECTED], and create an array with only the top ten
items in it. This seems like a lot of activity compared to
allowing the database to only return the top 10 items.
Maybe you could in code add a sort ordering and a result number
limit to your fetch specification. That only would work assuming
that the eo adapter can translate "[EMAIL PROTECTED]" to
appropriate SQL. Something you would have to try out. Looking at
EOModeler though, this is not supported. As it is not there in the
fetch spec builder. Still, might be worth a try.
Or, you could use a combination of those approaches... Something like:
1. Fetch the itemID values from the RATING table with SQL, using
something like:
SELECT ITEM_ID FROM RATING
GROUP BY ITEM_ID
ORDER BY AVG(RATING) DESC
RETURN RESULTS 10
Uhm, *something like* this, I am not sure this is correct. "RETURN
RESULTS" is OpenBase specific I think, I don't really know the
standard keyword for limiting the number of returned results.
2. Use an EOModel created fetch specification that has a
qualification binding on item.itemID and bind the previously
fetched IDs to it in code.
This is sweet as there is only one place where you have to worry
about SQL maintenance.
Hope this helps,
Flor
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