Hi,

Given a class:



CollectionOfThings should only contain BaseClasses of only one type:
==> If type=1, initialise with FirstDerivedClass
==> if type=2, initialise with SecondDerivedClass

Is there a way to do this or is it better just to subclass SomeClass so that each subclass a list of specific types? This presumably would be very easy with the table-per-hierarchy design, and might arguably be cleaner anyway.

Thanks,

Steve

Assuming that you don't intend to change the type used in the collection at runtime, subclassing sounds like a better approach to me. You could still use the SomeClass base (abstract I assume) along with the abstract factory pattern to get the appropriate subclass at runtime (if applicable).

You could even have the base class and subclasses in the same table and put the discriminator (int Type) in the subclass mappings so that you only get collections of the desired type.

Having the discriminator in the code itself, however, would require for you to get the desired type programmatically.

Hi,

Yes, you're probably right; I think it's something I'd have just done myself with ADO (initialised after construction, limited access to the collection and controlled what was in it programmatically) but it's probably more correct to subclass for the type safety.

Thanks,

Steve

[See later post for better formatting]

Further to this, is it possible for a three level hierarchy:

to use a mix of subclass methods?

For example, if the table storing BaseClass has the type parameter that determines the type of DerivedClassTypeX but SomeClass involves a join to another table?

E.g.

I guess this could get confusing, but it doesn't seem that weird.

Steve