Re: gdl2, filtering objects for display group

[David Ayers]

Dirk Lattermann wrote:

> I have set up a EODatabaseDataSource for A and a EODetailDataSource
> for B with corresponding EODisplayGroups and an
> EOMasterDetailAssociation between the two. Displaying data from
> these instances works ok, and I get to see the values of B that are
> in relation to the selected value of A.
>
> Now, I want to restrict the values of B to those that don't have
> any related records in C.
>
> 1. Should I do this in restricting the EODetailDataSource or the
> EODisplayGroup for B? (Are both possible?)

Acutally I can't give you an answer off the top of my head right now 
about whether there is a "true and correct" way, but restricting the 
EODisplayGroup should work.

> I tried restricting the EODisplayGroup for B in the following way:
> I created a subclass of EOGenericRecord adding a method
>
> -(int) numC
>
> that returns the number of objects in the array containing the related
> objects of C. I tested [[dgB selectedObject] valueForKey: @"numC"] and
> it worked.
>
> I then created an EOQualifier and qualified the display group:
>
> qual = [EOQualifier qualifierWithQualifierFormat: @"numC > 0"];
> [dgB setQualifier: qual];
>
> When fetching data, I got 
>
> NSUnknownKeyException: Unable to find value for key

hmm...

> I looked in EODisplayGroup which seems to use (unfortunately, I
> cannot debug) filteredArrayUsingQualifier: on the allObjects array.
> I now tried manually:
>
> [[dgB allObjects] filteredArrayUsingQualifier: qual] and got
>
> NSInvalidArgumentException: EOEntity(instance) does not recognize isEnabled
>
> on stderr, the message
> Exception occured while loading model: Unable to find value for key
> appears some lines before.

Hmm this seems strange also, maybe you could send the EOModel (if you 
want privatly).

> 2. Is it ok that the NSArray addition filteredArrayUsingQualifier:
> needs an entity (which it apparently does)?

GDL2 does a lot of lazy resoltion of EOModel information.  It seems this 
is an issue with EOAccess that just heppens to get triggered here.

> 3. Can/should I add an object property numC to the entity so that it
> can be properly queried? I failed because there is no corresponding
> attribute/column in this entity resp. table.

Even if you make it read-only

> 4. How can I "qualify" the detail data source so that only the right
> objects are fetched in the first place, without them needing to be
> filtered later?
>
> 5. Is this the right approach to model such situations (those that
> originate from queries "where not exists + subselect")?

Maybe you can send me example code to debug.  I don't have much time but 
hopefully I can find the issue more quickly that way.

Cheers,
David