I’ve been using the GetObjectStateEntry method for a while so that I can view and interact with the state of a particular entity that I have in hand.

Today I used the plural version of this method for the first time and boy do I like it!

GetObjectStateEntries takes as a parameter an EntityState enum: Added, Modified, Deleted, Unchanged or Detached.

It provides a perfect opportunity to do some work on entities prior to hitting the datastore during a save changes event.

For example, if you have an entity with a property to track the modification date you could update that property any time any other property in the entity is changed which might be wasteful. But with the GetObjectStateEntries method, I am able to just update the Modified Date property on all changed objects at once just before I save changes.

Here’s some code for dealing with the Customer entity that is derived directly from the customer table in the AdventureWorks database.

Now, this poses an architectural question and you may want to put this particular business logic elsewhere, but it’s merely a demonstration of what you can do with this method.

Because the generated classes are partial classes, I just create another partial class for my AdventureWorksLTEntities class and intercept the SaveChanges method. Then I grab all of the modified objects, use the Entity property to filter just Customers, then changed the Modified Date property. Next I grab the Added objects, change the Modified Date and also add in a default password hash and password salt. These are required for customer rows. (Read more about hashing passwords here on Beth Massi’s blog.)

Namespace AdventureWorksLTModel
 
  Partial Public Class AdventureWorksLTEntities

    Private Sub AdventureWorksLTEntities_SavingChanges(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.SavingChanges
      Dim changedEntities = Me.ObjectStateManager.GetObjectStateEntries(EntityState.Modified)
      For Each stateEntryEntity In changedEntities
        If TypeOf stateEntryEntity.Entity Is Customer Then
          Dim cust As Customer = stateEntryEntity.Entity
          cust.ModifiedDate = Now
        End If
      Next
      Dim addedEntities = Me.ObjectStateManager.GetObjectStateEntries(EntityState.Added)
      For Each stateEntryEntity In addedEntities
        If stateEntryEntity.Entity.GetType() Is Customer Then
          Dim cust As Customer = stateEntryEntity.Entity
          cust.ModifiedDate = Now
          ‘password hash cannot be null
          ‘for demo purposes just put a default string in there
          Dim strPassword As String = “p@ssw0rd”
          Dim encoder As New System.Text.UTF8Encoding()
          Dim SHA1Hasher As New Security.Cryptography.SHA1CryptoServiceProvider
          Dim hashedBytes As Byte() = SHA1Hasher.ComputeHash(encoder.GetBytes(strPassword))
          cust.PasswordHash = Convert.ToBase64String(hashedBytes)
          ‘customer table also needs salt for hash
          Dim buffer() As Byte = New Byte(5) {}
          Dim rng As New System.Security.Cryptography.RNGCryptoServiceProvider()
          rng.GetBytes(buffer)
          cust.PasswordSalt = Convert.ToBase64String(buffer)
        End If
      Next
    End Sub

  End Class
End Namespace

I have a feeling that this existed in Beta2, but I have updated both of my boxes and don’t feel like digging into a VPC just to verify.

One of the changes with the new CTP release of ADO.NET Data Services (formerly Astoria) is that you can create a service against any iQueryable, not just Entity Framework. This is huge.

Roger Jennings points to Guy Burstein’s how-to with Astoria (I guess it’s time to update my own now outdated posts) and makes the following comment:

“Like Andy Conrad, Guy uses LINQ to SQL instead of the Entity Framework as the data source. I have the feeling this substitution will become universal, at least until RDBMS vendors other than Microsoft deliver EntityClient data providers.”

So this bugs me a little. Why? Because the issue is that right now, Entity Framework only works with SQL Server. But hello, what do you people think LINQ to SQL works with? It’s called LINQ to SQL for a reason! 😉

Okay, rant over, back to work…

I’ve done this demo many times in conference and user group sessions. Someone on the ADO.NET forums asked how to do it and I thought I would just do a quick tutorial with screenshots.

What this Tutorial does is demonstrate how to create and use a data source from a particular entity in the model. I’m just doing simple drag and drop and no filtering or anything here with the goal of just a quick basic walkthrough for getting started.

Start by creating a Windows Application.

Add an Entity Data Model.

Select Data from the menu and choose Add New Data Source

In the first page of the wizard, choose Object as your Data Source Type.

The next screen of the wizard will show the namespaces in the current solution. Open up the namespace for the application

then choose the entity which you want to use as a Data Source. I will pick customer.

Then you can Finish the Wizard.

Now to get easy access to the datasource, go back to the menu and choose Show Data Sources from the Data menu.

The DataSources Window will be placed in your IDE in it’s default location. Mine docks with the windows on the left.

When it’s not pinned it gets tucked away with the others. You can undock it and put it wherever you want.

I can now drag and drop the customer data source onto the windows form to get the automatic DataGridView and Navigation toolbar (this is normal behavior for DataSource and not specific to Entity Framework).

There are a few more steps to actually getting user interaction with this. You need to populate the Binding Source and if you want to edit, you’ll need to add a little code to the save button on the toolbar.

You’ll need to enable the BindingNavigatorSaveButton (just click the save icon on the navigator toolbar and change it’s Enabled property to True). Additionally, you’ll probably want to format the grid which you can do easily from it’s SmartTag and more thoroughly through the properties window.

Here’s what the code behind looks like in my form enabling me to view, add, delete, edit and save data.

Imports WindowsApplication1.AdventureWorksLTModel
  Public Class Form1
   Private aw As AdventureWorksLTEntities
   Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) _
    Handles MyBase.Load
     aw = New AdventureWorksLTEntities
     CustomerBindingSource.DataSource = aw.Customer.OrderBy(Function(cust) cust.CompanyName)
   End Sub
   Private Sub CustomerBindingNavigatorSaveItem_Click(ByVal sender As System.Object, _ 
   ByVal e As System.EventArgs) Handles CustomerBindingNavigatorSaveItem.Click
     aw.SaveChanges()
   End Sub
 End Class

Note that because the AdventureWorks Customer table has the following constraints: ModifiedDate must be a valid date value and the PasswordHash and PasswordSalt fields cannot be Null, I have extended the entity class to take care of these things when SaveChanges is called.

Finally it’s real live production bits to play with!!

In addition to finally using real bits, key to this release are the finalization of response formats (XML by way of ATOM and JSON), security, an AJAX client, querying with LINQ when you are using one of the clients. THere’s a lot more.

Mike Flasko published 4 blog posts on the Astoria Team weblog yesterday:

ADO.NET Data Services (“Project Astoria”) CTP is Released

ADO.NET Data Services Dec2007 CTP – Validation and Access Control

LINQ to ADO.NET Data Services