Developers have been playing with LINQ to SQL long enough now that they are past the “how to” and thinking about performance. Jim Wooley blogs about LINQ to SQL Perf and using CompiledQuery.Compile to get the best performance. He also points to a series of posts on LINQ to SQL Performance by msdn blogger, Rico Mariani.

Of course, the next question for me is how LINQ to SQL will compare to LINQ to Entities and some of the other methods of extracting data via Entity Framework. While Entity Framework is still in earlier stages than LINQ to SQL and I’m guessing they are still working out perf, I did ask about this on the ADO.NET Orcas forums and was told that they’ll be working on writing something up about this.

It took me a while to figure out what caused this problem, so I thought I’d share it here.

I was trying to write a query in VB to grab customers who have orders placed after July 1, 2007.

The query looks like this:

Dim q = From cust In nwentities.Customers _
  Where (cust.Orders.Any(Function(o) _
     o.OrderDate > New DateTime(2007, 7, 1)))

But it would not compile. I have Option Strict On and the error was

Option Strict On disallows implicit conversions from ‘Boolean?’ and ‘Boolean’.

What the heck was this “Boolean?”. Not google-able, that’s for sure!

Then I noticed that OrderDate was being defined as a “Date?”.

What I’m seeing is the shortcut for Nullables in VB. It’s really hard to google for that. But if you look it’s everywhere! Such as in this post by Bill McCarthy. (See Bill? I found it all by myself! :-))

OrderDate is nullable. “Date?” means nullable date.

And the VB’s compiler is casting the entire expression to a nullable Boolean then telling me “Yo! A Nullable boolean is NOT the same as a boolean! Sorry”.

Note that the designer showed Nullable as false but the actual database has Nullable=true.

So, while I can write a regular query with this model, such as:

and I can write my exact query in C# with no worries:

   var q=from cust in nw.Customers where cust.Orders.Any(o=>o.OrderDate>new DateTime(2007,7,1)) select cust;

I believe that in my scenario, I just need to rethink my query. But later…

The new Entity Framework tools create an EDMX file which contains all three models: Conceptual, Mapping and Storage, in one file. When your project is built, individual files are created for the models, in the [familiar to those who have been using Entity Framework already] CSDL (conceptual), MSL (mapping) and SSDL (storage) files.

The connection string used by the Entity Framework contains not only the database connection string, but a metadata parameter with pointers to the three mapping files separated by a pipe character.

The Default Locations

Assuming that you put your EDM in the main folder of your project, in Windows Forms, Console and Class Library projects, you will see by default:

connectionString=
“metadata=.\Model.csdl|.\Model.ssdl|.\Model.msl;provider=System.Data.SqlClient;provider connection string=’Data Source=.\SQLEXPRESS;AttachDbFilename="C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Data\AdventureWorksLT_Data.mdf";Integrated Security=True;Connect Timeout=30;User Instance=True'”

When the project is built, those 3 files will land in the debug or release folder of the BIN directory for the app.

In a web app, the default location is different:

connectionString=
“metadata=~/bin/Model1.csdl|~/bin/Model1.ssdl|~/bin/Model1.msl;provider=System.Data.SqlClient;provider connection string=’Data Source=.\SQLEXPRESS;AttachDbFilename="C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Data\AdventureWorksLT_Data.mdf";Integrated Security=True;Connect Timeout=30;User Instance=True'”

This pushes the files into the bin folder of the site as well.

Sharing EDM with another project or another developer

If you have your EDM in it’s own project and then want to reference it from another project, you need to perform two steps.

1) Add a reference to the compiled DLL which represents the EDM.
2) Modify the config file of your consuming application to point to the location of the csdl, msl and ssdl files.

Here is an example of  a web.config’s connection string at design time that needs to use a model which is in a different project folder. I had to manually enter this long file path. Yucch.

connectionString=”metadata=C:\Documents and Settings\julie\My Documents\Visual Studio 2008\Projects\EFBeta2Windows\AdventureWorksModel\bin\Debug\Model.csdl|
 C:\Documents and Settings\julie\My Documents\Visual Studio 2008\Projects\EFBeta2Windows\AdventureWorksModel\bin\Debug\Model.ssdl|
 C:\Documents and Settings\julie\My Documents\Visual Studio 2008\Projects\EFBeta2Windows\AdventureWorksModel\bin\Debug\Model.msl;
provider=System.Data.SqlClient;
provider connection string=’Data Source=.\SQLEXPRESS;AttachDbFilename="C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\Data\AdventureWorksLT_Data.mdf";Integrated Security=True;Connect Timeout=30;User Instance=True'” providerName=”System.Data.EntityClient” />
   

There’s a better way

In the ADO.NET Orcas forums, Craig Lee pointed out that the build task for EDMDeploy which creates these files is placed in the project file and can be edited. I went looking.

You can get at it right in the UI for editing the project.

Go to the Compile tab, then to Build Events.

You can see the EdmxDeploy code in the Post-build event command line.

By editing, you can see the whole thing and the target directory parameter.

I changed the target to point to an existing (easy access for demos!) folder on my drive.

Then after I built the model project again, the csdl, msl and ssdl files were all in c:\efmodels\aw.

Now I can easily modify the metadata paths of any projects that consume my model to simple paths such as “C:\efmodels\aw\model.csdl”.

If I am in a team environment, then my files need to be available on a shared location or from source control.

Just to see another aspect the before and after difference of serializable EntityKeys in the Beta2 of EntityFramework, I simply stored a single Customer entity into viewstate, posted back and then looked at the entity in debug to see that yes, the EntityKey is there.

I went back to my Beta1 VPC and when I try to add a single customer entity object to viewstate, I get all kinds of serialization errors. No point in analyzing them since it works now.

I’ll probably explore some asp.net databinding scenarios next.

In the forums, Craig Lee responds to the  problem reported in this thread:

We are planning on releasing an FAQ of known issues, but here is a preview to see if this helps you.

Issue
Visual Studio displays a Package Load Failure error message for Package ‘Microsoft.Data.Entity.Design.Package.MicrosoftDataEntityDesignPackage’ when you double-click on a .edmx file

Workaround

This issue is caused by earlier installations of the MCrit June CTP.

1.    If it is installed, uninstall the ADO.NET Entity Framework Tools CTP from “Add/Remove Programs” in control panel

2.    Use gacutil.exe to verify that the following DLLs are not in the GAC. 

a.    Microsoft.Data.Entity.Design.dll

b.    Microsoft.Data.Entity.Design.EntityDesigner.dll

c.    Microsoft.Data.Entity.Design.Package.dll

d.    Microsoft.Data.Tools.XmlDesignerBase.dll

3.    Use Regedit.exe to check for and remove the CodeBase value from the registry at:

a.    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\9.0\Packages\{8889E051-B7F9-4781-BB33-2A36A9BDB3A5}

4.    Reinstall the the ADO.NET Entity Framework Tools CTP

I have not been able to stop thinking about EntityKeys, serialization and web services since my post about them yesterday, so I have done a little more experimentation tonight.

ObjectContext does have an AttachTo method. In my scenario of the incoming object from a web service client, the EntityKey is not available as part of the SalesOrderHeader entity because that is currently not being serialized as part of the entity. Note that this is a bug that the Entity Framework team is aware of and will fix.

While Attach allows you attach an entity that has a key, AttachTo does not require the EntityKey. However it does require that you know the name of the EntitySet.

In the type of testing scenario that I am working with , this is not a big problem.

While Attach would let me call

MyObjectContext.Attach(MyEntitythathasanEntityKey)

AttachTo has me call

MyObjectContext.Attach(MyKeylessEntity,”TheEntitySet”)

Once I do this, the EntityKey is created.

Note the contents of an entity key:

It has the name of the EntitySet in it. (I did not fix up the EntitySet names that the wizard created. I should have done this right after the wizard, and the new designer makes that really easy to do now.) That should be SalesOrderHeaders (plural)).

The EntitySet is nowhere else in the definition of my “incoming” SalesOrderHeader.

So if I didn’t happen to know the name of the EntitySet, I wouldn’t be able to attach it. If I want to have a generic updater, this could be a problem.

And a word or two hundred about concurrency:

The EntityKey itself has no impact on how to handle updates in the service.

As with LINQ to SQL, when I attach an object, it attaches as an unmodified entity. SaveChanges does nothing. The entity keeps track of original and modified values (which you can actually see if you create an ObjectStateEntry object from the entity). I actually tried attaching another instance of the object with different values, then attaching my incoming one to see if the 2nd instance would be seen as modified. No go. (Yah – grabbing at straws…and random ones at that!)

I tried calling Refresh with the ClientWins parameter (along with an array that contained my entity) to see if I could get the database to push it’s original values into the entity and somehow get the incoming values to magically become modified values. There have to be modified values to begin with for any of this to work. That doesn’t change anything because the state of the entity is still unmodified since the time I attached it.

The next thing I tried was updating the ModifiedTime property to see if kicking the ModifiedState of the entity would force all of my changes to get saved. Only ModifiedTime was saved, not the other values that were different.

The last thing I tried was, after attaching the entity, change the value using this funny method:

mySalesOrder.Comment=mySalesOrder.Comment

AND IT WORKED!

The entityState became modified and the Comment column was updated in the database.

So at this point, it still looks like there is no way around explicitly updating the entity properties in order to get them to be seen as modified. But I have no way of knowing WHICH of these things have been changed. Which leaves me a few options (probably more than just these three):

• Update every property
• Cache the entities when they are retrieved from the database (though I have to figure out what I want to cache… a dataset? an entire ObjectContext? … then I have to make decisions about keeping that refreshed).
• Grab the current data from the database just before I want to update. There are also potential concurrency issues with this as well.
• Iterate through each property and, using the ObjectStateEntry, set them as modified using the SetModifiedProperty, which takes the property name (string) as a parameter. I could do this in conjunction with data from the database or data from some cached store and only do this to properties that are different.

However all of these options seem to rely on knowing the name of the properties and I have not been able to find a way to programmatically discover them.

Therefore, it seems that I may have to go down one of these paths:

1. Use reflection to iterate through all of the properties and update them. My feeling about having to go to these lengths is “just no!” Plus this will mean that every property will be seen as modified and will get updated.
2. Write updaters for every entity that will explicitly set each property. That’s a crap load of data access code and not having to write a crap load of data access code is one of the benefits of Entity Framework.
3. Hope and pray that the EntityFramework team can somehow give us a way of attaching an object for original and one for modified. LINQ to SQL has this.
4. Wait for someone on the team to comment in my blog and show me the super easy obvious way that I have totally overlooked.

What’s a little funny to me is that Rick Strahl has had a similar conundrum with LINQ to SQL.

And I’m still only talking about full-on clientWins concurrency, so far.