core data subentities

FROM : Daniel Child
DATE : Fri Jan 11 21:29:55 2008

Hi all,

I have a basic question regarding the way subentities work in Core 
Data. My model has SuperEntity, SubOne, and SubTwo as the three 
entities, with SubOne and SubTwo having child relationships to 
SuperEntity. I was trying to test this "quick and dirty" prototype 
and found two problems.

The first is the layout. Dragging the models to Interface Builder, I 
get an NSArrayController for the table view of SuperEntity, and 
NSObjectControllers for the two "one-object" displays of subentities. 
But they are not linked, and I'm not sure how the bindings should be 
linked.

The second is conceptual. If I am going to be importing data 
corresponding to type SubOne, and then supplementing that with data 
from SubTwo, how exactly does that work. Is a SubOne object a 
SuperEntity with an additional attribute? The problem I especially 
envisage is if there is overlap. For instance, say they are 
dictionary words from different dictionaries.

(SubOne data entry)
lexeme: pen (superentity field)
IPA: (the IPA spelling) (superentity field)
definition: a writing implement (SubOne field)

(SubTwo data entry)
lexeme: pen (superentity field)
IPA: (the IPA spelling) (superentity field)
definition: a tool used for writing (SubTwo field)
etymology: xxxxx (another SubTwo field)

If I had imported the first data from a SubOne file, and then were 
importing data from a SubTwo file, I would not want to create a new 
record, but rather simply place the new information (definition and 
etymology) in the SubTwo portion. But in the real application 
(assuming I decide to use Core Data) I would in fact have many 
different types of word data, of which only a few fields (attributes 
like "lexeme") are common to all word data.

I know the above example is not that interesting, but it is the same 
concept as what I would be doing. I haven't seen any indication of 
how to handle subentities, or for that matter, an explanation of 
whether the attributes in SuperEntity and those in the SubEntities 
are considered part of one managed object or of separate managed 
objects. So even using KVC it is unclear to me how you would be 
referencing superentity and subentity attributes.

I've tried to read documentation but haven't seen any examples of 
this kind of structure. If anyone could give me a heads up or a super 
basic example of a similar thing, I'd really appreciate it.

Thanks.

Daniel