3.1, Regression, InMemoryDatabase: 'Nullable object must have a value.'

[yahorsi]

Hi Guys,

After migration from 2.2 to 3.1 our tests started failing. (Same code works just fine on 2.2 & the exact same data). In tests we use InMemory provider witch we instantiate following way

            var options = new DbContextOptionsBuilder<CrewPageContext>()
                .UseInMemoryDatabase("Test")
                .Options;
            var context = new DatabaseContext(options, AutoMock.Resolve<ILifetimeScope>());
            context.Database.EnsureDeleted();

And here is failing query:

        public Task<List<DutyEntityForLog>> GetForDayAsync(DateTime date, Guid personId)
        {
            var result =
                from d in Context.Duties
                join pd in Context.PersonDays on new { d.Date, d.PersonId } equals new { pd.Date, pd.PersonId } into pdJoin
                from pd in pdJoin.DefaultIfEmpty()

                join f in Context.Flights on d.FlightId equals f.Id into fJoin
                from f in fJoin.DefaultIfEmpty()

                where d.Date == date && d.PersonId == personId

                select new DutyEntityForLog
                {
                    Id = d.Id,
                    Date = d.Date,
                    ActivityId = d.ActivityId,
                    Title = d.Title,

                    FlightId = d.FlightId,

                    FlightNumber = f == null ? (int?)null : f.FlightNumber,
                    OriginRcd = f == null ? null : f.OriginRcd,
                    DestinationRcd = f == null ? null : f.DestinationRcd,
                    DepartureDateTimeUtc = f == null ? (DateTime?)null : f.DepartureDateTimeUtc,

                    DateTimeFromUtc = d.DateTimeFromUtc,
                    DateTimeFromDiffToLt = d.DateTimeFromDiffToLt,
                    DateTimeToUtc = d.DateTimeToUtc,
                    DateTimeToDiffToLt = d.DateTimeToDiffToLt,

                    BlockTimeSec = d.BlockTimeSec,
                    DutyTimeSec = d.DutyTimeSec,

                    SimulationId = d.SimulationId,
                    PositioningId = d.PositioningId,

                    VacationType = d.VacationType != null ? (VacationType)d.VacationType : (VacationType?)null
                };

            return result.ToListAsync();
        }

And the exception is following:

Message: 
    System.InvalidOperationException : Nullable object must have a value.
  Stack Trace: 
    lambda_method(Closure , ValueBuffer )
    WhereSelectEnumerableIterator`2.MoveNext()
    AsyncEnumerator.MoveNextAsync()
    Enumerator.MoveNextAsync()
    EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable`1 source, CancellationToken cancellationToken)
    EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable`1 source, CancellationToken cancellationToken)
...

Query fails only in some cases, I'm trying to isolate it and build small repo but it might take some time.

[yahorsi]

I had finally some time to reproduce the problem. Here is the smallest sample to demo the problem. Works on 2.2.6 and throws on 3.1 & 3.1.1 (didn't check on 3.0)

using Microsoft.EntityFrameworkCore;
using System;
using System.Linq;

namespace Ef311NullableEnumBug
{
    public enum Bar
    {
        value1,
        value2
    };

    public class FooTable
    {
        public int Id { get; set; }
        public byte? Bar { get; set; }
    }

    public class DatabaseContext : DbContext
    {
        public DbSet<FooTable> FooTable { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder
                .UseInMemoryDatabase("Test");

            base.OnConfiguring(optionsBuilder);
        }
    }


    class Program
    {
        static void Main(string[] args)
        {
            var context = new DatabaseContext();

            context.FooTable.Add(new FooTable { Id = 1, Bar = null});
            context.SaveChanges();

            context = new DatabaseContext();
            var query = from foo in context.FooTable
                        select new
                        {
                            Bar = foo.Bar != null? (Bar)foo.Bar : (Bar?)null
                        };

            var r = query.ToList();
        }
    }
}

NOTE: If we change the first cast from (Bar) to (Bar?) - it fixes the exception

[yahorsi]

Hi Guys, no plans to fix this in Or 3.1 or 5.0 ? That is regression...

[smitpatel]

There is easy work-around to fix the error.

[yahorsi]

Correct, ok for me, if we could list this as a breaking change.
Imagine we have tents of projects to migrate and tons of queries to fix.

[smitpatel]

Note to implementer: NullCheckRemovingExpressionVisitor should probably remove that cast to non-null and identify this specific pattern.