Re: EOFetchSpecification with SQL
Re: EOFetchSpecification with SQL
- Subject: Re: EOFetchSpecification with SQL
- From: Jonathan Rochkind <email@hidden>
- Date: Wed, 20 Aug 2003 10:36:02 -0500
At 01:22 PM 8/20/2003 +0300, Alex Blaj wrote:
Hello again,
Is there any way to create a fetchSpecification using a String that contains
the SELECT statement for that fetchSpec?
Well, yes, you CAN specify the entire raw SQL for a fetch
specification. If the fetch spec is fetching full EOs, you've got to make
sure to have all the columns included in your entity, in the right
order. If the fetch spec is just fetching raw rows, you can do what you
want (but might as well use EOUtilities.rawRowsForSQL instead).
EOFetchSpecification spec; //assume exists
String sqlQuery; //assume exists
NSMutableDictionary hints = new NSMutableDictionary();
hints.setObjectForKey( sqlQuery,
EODatabaseContext.CustomQueryExpressionHintKey);
spec.setHints( hints );
====
Now, just because you CAN do this doesn't mean you really should. From a
maintainability standpoint, from the design goal of seperate layers, it's
really undesirable to have raw SQL hardcoded into your app. If you find
yourself doing this in all but the most rare and unusual
circumstances---either you are doing something wrong, or EOF may not be a
good tool for you.
If you just want to manually write the "WHERE" part of the SQL query, not
the entire query, you can do that with the EOSQLQualifier instead---the
same caveats apply.
Or, if I declared a new fetchSpecification, it there a way to set its bindings
so that it corresponds to my SELECT (String) statement.
Not sure what you mean.
I'm using a query like this: (SELECT ...) INTERSECT (SELECT ...).
Ah, that INTERSECT is going to be tricky. I can't think of a good way to
get EOF to generate a query with that kind of INTERSECT in it. You could
just give up and fetch both seperate querries into memory, and then do the
intersect in memory with NSSet/NSMutableSet. If the data isn't
prohibitively large.
Or, if I use the rawRowsForSQL method, is there a "nice" way of getting the
results as I would get them from objectsWithFetchSpecification (instead of
creating an array of objects and set all their attributes to what I got from
rawRowsForSQL)?
If you use rawRowsForSQL, it will just return raw rows---not EOs. You can
turn these raw rows into EOs later, as long as they contain primary key
information (see EOUtilities.faultForRawRow and EOUtilities.objectForRawRow
), but the operation to turn the raw row into an EO may require another
round trip to the db---in some cases one round trip per row, but this can
be made more efficient sometimes.
If you use an EOFetchSpecification, as I explained above, you _can_ specify
the raw SQL yourself. If you want actual EOs to be returned, you've got to
make sure the right columns are returned in the right order. If you later
add columns in EOModeler, it may break your hard coded SQL, which is
another reason to avoid it.
Hope this helps,
--Jonathan
Thanks,
Alex.
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