The video from my webcast, Top 10 Treats in Entity Framework 4 is available on Oreilly’s website: http://www.oreillynet.com/pub/e/1517.

I just discovered that WebEx saved the chat window from my O’Reilly webcast last month. So I thought I would pick out the quesitons and answer them here although I did answer some of them at the end of the webcast:

Q address NOT Address??

Someone noticed that an entity was named address. The pluralization support in the VS2010 EDM Designer does not fix up bad capitalization from the database which this was meant to highlight. Another viewer replied: it’s address and not Address because the original table was with a lower case ‘a’. VS2010 supports pluralization, but doesn’t change capitalization

Q These classes are not POCO, correct? What do I have to do to have POCO and generate db schema?

In the early part of the demo I was wroking with the default EntityObjects. To use POCO classes to generate db schema you’ll want to skip the model and use the Code-Only support that is part of the EF Feature CTP: Updated Feature CTP Walkthrough- Code Only for Entity Framework

This is awesome. We will all forgot how to sql.
Not a question, but a funny comment I wanted to share.

Q What about update database from model?

Update database from model has been supported sine the first version of EF. It will bring in new tables and new properties in tables but it will not modify property types. Be aware that any changes made manually to the SSDL get overwritten during this process.

Q. How much control does the developer have over the generated SQL DDL?
I answered this one at the end of the webcast. There is a T4 template that drives the DDL generation so that’s customizable.

This thing needs a pause button! LOL
Another funny comment I thought I would share. Yeah it is tough doing these webcasts that have a time limit! 🙂

Q. can you control lazy loading on a per entity level?
I happened to answer this question as I was talking about lazy loading and the person who asked then said: “ah thanks … ok, so per context only.”

Q. How easy is it to mock entities for nUnit or xUnit testing?

The new IObjectSet interface makes it totally possible to mock entities now. Many people have written blog posts about this. Here’s mine: http://thedatafarm.wpengine.com/blog/data-access/agile-entity-framework-4-repository-part-5-iobjectset/

Q: I heard something about "model functions" or "schema functions", implying I can do calculations for fields OR create views over entities in the EDM / .edmx file. Is this true?
Yes. Check out http://thedatafarm.wpengine.com/blog/data-access/ef4-model-defined-functions-level-1-amp-2/

Q: how does Oracle support compare? Is it as functionally complete? Is it as stable/bug free?

Oracle providers are available from DevArt and Data Direct. As far as I know they are both very solid. Functionally complete? Dunno.

LINK to EF POCO Adapter for EF1: code.msdn.microsoft.com/EFPocoAdapter

I hit my head against a wall for a while today when I was trying to create a data service using my EF POCOs. I have my model & context in one assembly and my generated POCO entities in another.

When I ran the service (I had exposed all EntitySets for AllRead), I got the mysterious error:

The server encountered an error processing the request. See server logs for more details.

Even with config.UseVerboseErrors = true; in my service, the message did not change.

I finally saw the real problem first in Intellitrace (I’m using VS2010 and .NET 4.0) and then by setting the service behavior’s IncludeExceptionDetailInFaults to true.

This is what the detailed exception looks like:

The server encountered an error processing the request. The exception message is ‘Value cannot be null. Parameter name: key’. See server logs for more details. The exception stack trace is:

at System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument) at System.Collections.Generic.Dictionary`2.FindEntry(TKey key) at System.Collections.Generic.Dictionary`2.get_Item(TKey key) at System.Data.Services.Providers.ObjectContextServiceProvider.PopulateMetadata(IDictionary`2 knownTypes, IDictionary`2 childTypes, IDictionary`2 entitySets) at System.Data.Services.Providers.BaseServiceProvider.PopulateMetadata() at System.Data.Services.DataService`1.CreateProvider() at System.Data.Services.DataService`1.EnsureProviderAndConfigForRequest() at System.Data.Services.DataService`1.HandleRequest() at System.Data.Services.DataService`1.ProcessRequestForMessage(Stream messageBody) at SyncInvokeProcessRequestForMessage(Object , Object[] , Object[] ) at System.ServiceModel.Dispatcher.SyncMethodInvoker.Invoke(Object instance, Object[] inputs, Object[]& outputs) at System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeBegin(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage41(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage4(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage31(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage3(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage2(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage11(MessageRpc& rpc) at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage1(MessageRpc& rpc) at System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet

Key in here for me are “PopulateMetadata” and argument is null.

Looks like we can’t read the metadata, i.e. the CSDL, MSL and/or SSDL files. I’ve got he connection string in web.config so that ‘s not it.

With this info in hand, I found this forum post which clarified the issue: Fail to work with POCO ModelContainer which entities are located in

I neede to force the metadata to load into the application process. I have a handy trick for this which is simpler than the one suggested in the forum.

I blogged about it in 2008: Quick Trick for forcing MetadataWorkspace ItemCollections to load.

So, I added this override to the data service:

     protected override BAPOCOs CreateDataSource()
     {
       var context = new BAPOCOs();
       var tracestring = context.CreateQuery<Contact>("BAPOCOs.Contacts").ToTraceString();
       return context;
     }

Note that calling ToTraceString does not cause a command to be executed on the server.

And my service was back in working condition, however…

There is one thing I’m not happy with. I originally had a test in there to see if the metadata was already loaded. If so, then no need to call ToTraceString. The metadata is supposed to remain in teh app process so after the first hit, I should be skipping the ToTraceString code. However, it was being hit every time and if I forced it to skip, then I was back to the original error.

This seems like an expensive waste of resources and if that’s the case, I’m doing it on EVERY call, I’d rather use the more complex code which explicitly loads the MDW rather than my little trick which is not a big deal if I’m only doing it once. The upside is that this is essentially an Entity SQL query and by default ESQL queries are cached and do not need to be recompiled. So perhaps it’s not so bad. Either way, I’d like to get this solution to a more satisfactory state.

I have asked about this in the above mentioned forum thread.  And will add to this blog post when I get more info.