Well, this change really came in the March 2011 CTP but I didn’t realize it until the June CTP was out, so I’ll call it a wash.

WCF Data Services has had a bad problem with inherited types where the derived type had a relationship to yet another type. For example, in this model where TPTTableA is a derived type (from Base)and has related data (BaseChildren).

If you expose just the Bases EntitySet (along with its derived type) in a WCF Data service, that was fine. I can browse to http://localhost:3958/WcfDataService1.svc/Bases easily.

But if I also exposed the related type (BaseChild) then the data service would have a hissy fit when you tried to access the hierarchy base (same URI as before). If you dig into the error it tells you:

“Navigation Properties are not supported on derived entity types. Entity Set ‘Bases’ has a instance of type ‘cf_model.ContextModel.TPTTableA’, which is an derived entity type and has navigation properties. Please remove all the navigation properties from type ‘cf_model.ContextModel.TPTTableA’”

Paul Mehner blogged about this and I wrote up a request on Microsoft Connect. Here’s Paul’s post: Windows Communication Foundation Data Services (Astoria) – The Stuff They Should Have Told You Before You Started

But it’s now fixed!

Using the same model, I can expose all of the entity sets in the data service and I’m still able to access the types in the inheritance hierarchy.

Here is an example where I am looking at a single Base entity and in fact this happens to be one of the derived types, notice in the category the term is cf_model.TPTA. The type is strongly typed.

You can see that strong typing in the link to the related data:

Bases(1)/cf_model.TPTA/BaseChildren

That’s how the data service is able to see the relationship, only off of the specific type that owns the relationship.

So accessing the relationship is a little different than normal. I struggled with this but was grateful for some help from data wizard, Pablo Castro.

The Uri to access the navigation requires that type specification:

http://localhost:1888/WcfDataService1.svc/Bases(1)/cf_model.TPTA/BaseChildren

You also need that type if you want to eager load the type along with it’s related data:

http://localhost:1888/WcfDataService1.svc/Bases(1)/cf_model.TPTA?$expand=BaseChildren

Note that I was still having a little trouble with the navigation (the first of these two Uris). It turns out that cassini (i.e. the asp.net Web Development Server) was having a problem with the period (.) in between cf_model and TPTA.

Once I switched the service to use IIS Express (which was my first time using IIS Express and shockingly easy!), it was fine. (Thanks again to Pablo for setting me straight on this problem.)

So it’s come a long way and if this is how it is finalized, I can live with it though I guess it would be nice to have the URIs cleaned up.

Of course you’re more likely to use one of the client libraries that hide much of the Uri writing from us, so maybe in the end it will not be so bad. I have not yet played with the new client library that came with this CTP so I can’t say quite yet.

Ahh another one of the very awesome features of the new CTP!

Pre-compiled LINQ to Entities queries (LINQ to SQL has them too) are an incredible performance boost. Entity Framework has to a bit of work to read your LINQ to Entities query, then scour through the metadata to figure out what tables & columns are involved, then pass all of that info to the provider (e.g., System.Data.SqlClient) to get a properly constructed store query. If you have queries that you use frequently, even if they have parameters, it is a big benefit to do this once and then reuse the store query.

I’ve written about this a lot. It’s a bit of  a PIA to do especially once you start adding repositories or other abstractions into your application. And the worst part is that they are tied to ObjectContext and you cannot even trick a DbContext into leveraging CompiledQuery. (Believe me I tried and I know the team tried too.)

So, they’ve come up with a whole new way to pre-compile and invoke these queries and the best part is that it all happens under the covers by default. Yahoo!

Plus you can easily turn the feature off (and back on) as needed. With CompiledQuery in .NET 3.5 & .NET 4.0, the cost of compiling a pre-compiling a query that can be invoked later is more expensive than the one time cost of the effort to transform a L2E query into a store query. Auto-Compiled queries work very differently so I don’t know if you need to have the same concern about turning it off for single-use queries. My educated guess is that it’s the same. EF still has to work out the query,then it has to cache it then it has to look for it in the cache. So if won’t benefit from having the store query cached, then why pay the cost of storing and reading from the cache?

I highly recommend reading the EF team’s walk-through on the Auto-Compiled Queries for information on performance and more details about this feature and how it works. Especially the note that this paper says CompiledQuery is still faster.

A bit of testing

I did a small test where I ran a simple query 10 times using the default (compiled) and 10 times where I’ve turned off the compilation. I also started with a set up warmup queries to make sure that none of the queries I was timing would be impacted by EF application startup costs. Here you can see the key parts of my test. Note that I’m using ObjectContext here and that’s where the ContextOptions property lives (same options where you find LazyLoadingEnabled, etc). You can get there from an EF 4.1 DbContext by casting back to an ObjectContext.

  public static void CompiledQueries()
    {
      using (var context = new BAEntities())
      {
        FilteredQuery(context, 3).FirstOrDefault();
        FilteredQuery(context, 100).FirstOrDefault();
        FilteredQuery(context, 113).FirstOrDefault();
        FilteredQuery(context, 196).FirstOrDefault();
      }
    }
    public static void NonCompiledQueries()
    {
      using (var context = new BAEntities())
      {
        context.ContextOptions.DefaultQueryPlanCachingSetting = false;
        FilteredQuery(context, 3).FirstOrDefault();
        FilteredQuery(context, 100).FirstOrDefault();
        FilteredQuery(context, 113).FirstOrDefault();
        FilteredQuery(context, 196).FirstOrDefault();
      }
    }

    internal static IQueryable<Contact> FilteredQuery(BAEntities context, int id)
    {
      var query= from c in context.Contacts.Include("Addresses") where c.ContactID == id select c;
      return query;
    }

I used Visual Studio’s profiling tools to get the time taken for running the compiled queries and for running the queries with the compilation set off.

When I executed each method (CompiledQueries and NonCompiledQueries) 3 times, I found that the total time for the compiled queries ran about 5 times faster than the total time for the non-compiled queries.

When I executed each method 10 times, the compiled queries total time was about 3 times faster than the non-compiled.

Note that these are not benchmark numbers to be used, but just a general idea of the performance savings. The performance gain from using the pre-compiling queries is not news – although again, auto-compiled queries are not as fast as invoking a CompiledQuery. What’s news is that you now get the performance savings for free. Many developers aren’t even aware of the compiled queries. Some are daunted by the code that it takes to create them. And some scenarios are just too hard or in the case of DbContext, impossible, to leverage them.

WCF Data Services

I mentioned data services in the blog post title. Because this compilation is the default, that means that when you build WCF Data Services on top of an Entity Framework model, the services will also automatically get the performance savings as well.

Enjoy!