.Net: [MEVD] Review our attribute design

[roji]

VectorStoreRecordDataAttribute and VectorStoreRecordKeyAttribute have no constructors, and only have properties (note that some have set;, others init;.

In contrast, VectorStoreRecordVectorAttribute has 4 constructors, with all but StoragePropertyName being private. The Dimensions property is a nullable int, but the parameter in the various constructors is non-nullable (though a parameterless constructor exists, allowing dimensions to not be set).

If we want to force the user to set the dimensions, we probably need to remove the parameterless constructor; otherwise, if it really should be optional, we could just make the property settable (or initable). The other properties - DistanceFunction and IndexKind which are already optional - can also simply be directly settable.

Note: a version of this was raised before by @dluc in #11265.
Note: when we decide here, make sure to take that into account in the new model (see #11264 (comment)).

[dluc]

Note: there are scenarios where Dimension shouldn't be mandatory:

• checking if a collection exists
• deleting a collection
• searching a non-existing collection (should return 404 rather than a bad request or other errors)

Also, there's a different approach where the code automatically detects the vector size, by the vector given during the first insert, when a collection is automatically created. This is the approach I've preferred in my apps, to reduce the need of changing conf, rebuilding code, etc.

[roji]

checking if a collection exists
deleting a collection

These are operations where an IVectorStoreRecordCollection (and/or record definition) shouldn't needed in the first place, i.e. they should be doable from IVectorStore, and so seem unrelated to this issue. The 2nd is already tracked by #10881 - I've added existence checking to that issue as well (as the two are pretty related).

This issue is about when you do need an IVectorStoreRecordCollection with a definition (e.g. because you want to search or do CRUD operations) - is a dimension required for that case.

searching a non-existing collection (should return 404 rather than a bad request or other errors)

This one I don't understand - how does the fact that a collection exist or doesn't exist relate to whether Dimension should be required or not? When MEVD sends a search to the database, it's oblivious to whether the collection exists or not (it could have existed a second ago but have been deleted in the meantime), can you explain a bit more on how you see this as relevant here?

(re the error/exception that gets thrown when trying to access a non-existing collection, you already reported that in #11282)