Entity Framework Question

nanonerd · January 6th, 2012, 04:11 PM

Hi Imar,

Got a Q about EF. I'm now working on a personal project where I have a slew of tables (combined with the default asp.net tables, about 15 I guess).

QUESTION: When I create the Entity Model File and I am to include tables, should I include all the tables? Or should I create separate EMF's to "chunk out" sets of tables ... My main concern is load time ... I'm unclear when and how things get loaded ... so from an architectural standpoint, I'm not sure whether to create one EMF and include all the tables there or create multiple EMF's and assign specific tables to each EMF ...

What is the best method to balance function and speed? Thanks.

- Nano

Imar · January 6th, 2012, 08:00 PM

Hi there,

Most of the time, I use a single edmx as it's much easier to maintain. Beyond 50 or 100 entities, you could consider splitting up the model. For more details:

http://blogs.msdn.com/b/adonet/archi...rk-part-1.aspx
http://blogs.msdn.com/b/adonet/archi...rk-part-2.aspx

Cheers,

Imar

nanonerd · January 14th, 2012, 02:20 PM

Hi, thanks for prior reply. I have another question on EF. Got stuck on it last night and this morning, narrowed it down WHERE the error is occurring but I do not understand WHY the error occurs.

Code:

var userCheck = (from check in profileEnt.scAccounts
                                 where check.asp_userId == userID
                                 select check).FirstOrDefault();

When I run this code, I get "Error: Sys.WebForms.PageRequestManagerServerErrorExceptio n: This property cannot be set to a null value."

#1 When I change FirstOrDefault() to Count(), it works: returns "1".

#2 When I remove FirstOrDefault(), it works: returns "System.Data.Objects.ObjectQuery`1[Sc2Saga.scAccount]"

#3 When I remove FirstOrDefault() and use Anonymous Types (e.g., Select new), it works.

When I replace FirstOrDefault() with SingleorDefault(), it fails.

So I see WHERE the error occurs, but I do not understand WHY it fails.

As a workaround, can I use step #2? If so, how do I retrieve the first record in the collection?

Help is greatly appreciated ...

- Nano

Imar · January 15th, 2012, 07:59 AM

Hi there,

FirstOrDefault tries to return the first instance in the sequence if there is one, otherwise, it returns null.

The other methods you tried still return a non-null value, even when they are no items in the sequence. In other words, the sequence is empty, but is still a valid object in .NET and not null.

Apparently, the code you're using this on doesn't like null values but can deal with empty sequences.

Hope this helps,

Imar