Saturday, 24 July 2010

Using Entity Framework from a different DLL in Dynamic Data

I just thought I should document what we learned in this thread here Entity Framework: Entity Model in a separated DLL first of all it is easy to do in Dynamic Data 4 and needs a fix on each page for Dynamic Data 1 (this version that shipped with Visual Studio 2008 SP1 and .Net 3.5 SP1)

Note: see also Rick Andersons blog post here Explicit connection string for EF and L2S

Adding Model from DLL or Class Library

Sample Project

Figure 1 – sample project with Model in Class Library

To use the Northwind Model in our project we need to get a new instance of the Northwind context, to do this we could add the code to instantiate it in the Glabal.asax.cs file. But for me the object of having it in an external class library/DLL is to keep it reusable, so I had the idea of building the connection string in the external class library rather than locally. We add Listing 1 to the class library, as a partial class of the NorthwindEntities class, pass-in the server name (we could pass-in more but the server name will do here).

public partial class NorthwindEntities
{
    /// <summary>
    /// Gets a new NorthwindEntities object.
    /// </summary>
    public static ObjectContext GetContext(String server, String database)
    {
        EntityConnectionStringBuilder entityBuilder = new EntityConnectionStringBuilder();
        entityBuilder.Provider = "System.Data.SqlClient";
        entityBuilder.ProviderConnectionString =
            String.Format("server={0};database={1};Integrated Security=SSPI;MultipleActiveResultSets=True",
            server,
            database);
        entityBuilder.Metadata = @"res://*";
        var objContext = new NorthwindContext.NorthwindEntities(entityBuilder.ToString());

        return objContext;
    }
}

Listing 1 – GetContext helper method

So now all we need to add this to our Dynamic Data app is use this in the RegisterContext method in the Global.asax.cs

DefaultModel.RegisterContext(() => NorthwindContext.NorthwindEntities.GetContext("aragorn","Northwind"),
            new ContextConfiguration()
            {
                ScaffoldAllTables = true
            });

Listing 2 – Using the GetContext helper

Fixing it up to work in Original version of Dynamic Data

This work beautifully in Dynamic Data 4, but not in the previous release Sadwe need the fix mentioned in Rick Andersons post

GridDataSource.ContextCreating += delegate(object ceSender,
    EntityDataSourceContextCreatingEventArgs ceArgs)
    {
        ceArgs.Context = (ObjectContext)table.CreateContext();
    };

Listing 3 – Fix for Dynamic Data 1

Added to the List page it looks like this:

protected void Page_Init(object sender, EventArgs e)
{
    DynamicDataManager1.RegisterControl(GridView1, true /*setSelectionFromUrl*/);
    GridDataSource.ContextCreating += delegate(object ceSender,
        EntityDataSourceContextCreatingEventArgs ceArgs)
        {
            ceArgs.Context = (ObjectContext)table.CreateContext();
        };
}

Listing 4 – Added to List page template

You have to add this to each page template and add it twice on the ListDetails page template.

4 comments:

Maxisam said...

Really appreciate your post ! It helps me a lot !

Steve said...

Your welcome :)

Steve

Anonymous said...

Hey Steve,
Nice post! I've been trying to define the metadata in a different project with the same namespace as of the Entity Context. but can't get it to working, any thoughts on this?

Steve said...

Hi there, this is not possible using a buddy/metadata class, I do have a solution on my blog for stiring metadata in the DB which would allow this.

Steve