Assigning boolean in Select statement throws invalid cast.

[VeronicaWasson]

I have a DbContext like this:

public class BookContext : DbContext
{
    public DbSet<Author> Authors { get; set; }
 }

This code throws an invalid cast

var x = BookContext.Authors
    .Select(x => new
    {
        Text = x.FirstMidName,
        Value = x.AuthorID.ToString(),
        Selected = true  // Throws invalid cast
    }).ToList();

Works fine without 'Selected = true'.

Stack trace:

System.InvalidCastException was unhandled by user code
  HResult=-2147467262
  Message=Specified cast is not valid.
  Source=EntityFramework.Relational
  StackTrace:
       at Microsoft.Data.Entity.Relational.RelationalObjectArrayValueReader.ReadValue[T](Int32 index)
       at lambda_method(Closure , QuerySourceScope )
       at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
       at Microsoft.Data.Entity.Query.LinqOperatorProvider.ExceptionInterceptor`1.EnumeratorExceptionInterceptor.MoveNext()
       at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
       at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
       at ContosoBooks.Controllers.BookController.GetAuthorsListItems(Int32 selected) in C:\Users\mwasson\Documents\Visual Studio 2015\Projects\sample\src\ContosoBooks\Controllers\BookController.cs:line 143
       at ContosoBooks.Controllers.BookController.Create() in C:\Users\mwasson\Documents\Visual Studio 2015\Projects\sample\src\ContosoBooks\Controllers\BookController.cs:line 45
  InnerException: 

[maumar]

Problem here is that we are sending the following query to the database:

SELECT [x].[FirstMidName], [x].[AuthorID], 1
FROM [Author] AS [x]

This then gets stored in the value buffer as {string, int, int}, rather than {string, int, bool} - hence the conversion fails, when we try to cast from int to bool.

Possible solution is to evaluate the constant on the client, rather than sending it to server. We need to make sure that we still translate constants that are bound to the source query somehow (part of a more complex expression involving a column, or an argument to a function)

[divega]

Wouldn't CAST (1 AS BIT) work?

[maumar]

It would, and would be a simpler solution. However the other solution seems to be consistent with our funcletization strategy (funcletize as much as we can if its deterministic and doesn't bring more rows from the database).

[anpete]

Yes, better to do client eval here as it means less data on the wire.

[divega]

Agreed, but any idea of how much work it would take each way? We need to be careful not to turn this little thing into something big 😄

[anpete]

Well, it shouldn't be too bad as we can already do the client eval. I will follow up with @maumar later today for an update.

[maumar]

I think we got a very easy/local fix for this

[maumar]

Fixed in e8e50c0