Question

I am trying to use SQL Server CE on Windows Phone Mango. Here is my DataContext:

public class FooDataContext : DataContext
{
    private static readonly string DB_CONNECTION_STRING = "Data Source=isostore:/foo.sdf";

    // Pass the connection string to the base class.
    public FooDataContext() : base(DB_CONNECTION_STRING)
    { }

    // can this be a property?
    public Table<Foo> Items;

    public void ClearDatabase()
    {
        if (DatabaseExists())
        {
            DeleteDatabase();
        }
    }

    public void EnsureDatabaseExists()
    {
        if (!DatabaseExists())
        {
            CreateDatabase();
            SubmitChanges();
        }
    }
}

In the constructor of the main page, I call EnsureDatabaseExists(). If I’ve changed the schema, I also include a call to ClearDatabase():

//fooData.ClearDatabase();
fooData.EnsureDatabaseExists();

Foo‘s columns are int, double, and DateTime. When I run the app without the ClearDatabase() call, I get the following error as soon as I try to access fooContext.Items:

The specified table does not exist. [ Foo ]

What is going on here? If I freshly install the app, everything works fine.

Answer 1

The backing table structures for a Linq To SQL DataContext are only created when CreateDatabase() is called, or when you explicitly update the schema through the DatabaseSchemaUpdater.Execute() method.

I suspect what is happening in your case, is that you are adding a new entity type to your data model, however you are not actually updating the schema via DatabaseSchemaUpdater. This results in Linq To SQL generating a query which references a table which has not yet been created within the database engine.

I would recommend that you check out the DatabaseSchemaUpdater class if you want to be able to handle schema changes in your application.

http://msdn.microsoft.com/en-us/library/hh133477(v=VS.95).aspx