EF Core InMemory database throws an argument exception on Nullable<>.ToString

[wilfriedb]

After upgrading to EF Core 9, a unit test using the InMemory database throws this exception:

System.ArgumentException
  HResult=0x80070057
  Message=Method 'System.String ToString(System.String)' declared on type 'System.DateOnly' cannot be called with instance of type 'System.Nullable`1[System.DateOnly]'
  Source=System.Linq.Expressions
  StackTrace:
   at System.Linq.Expressions.Expression.ValidateCallInstanceType(Type instanceType, MethodInfo method) in /_/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/MethodCallExpression.cs:line 1265

This is from the Microsoft.EntityFrameworkCore.InMemory package.

When I look into this package code where the exception originates, I see the following change between version 8 and version 9:

EF Core 8:
Namespace Microsoft.EntityFrameworkCore.InMemory.Query.Internal
InMemoryExpressionTranslatingExpressionVisitor.cs line 888:

        // if object is nullable, add null safeguard before calling the function
        // we special-case Nullable<>.GetValueOrDefault, which doesn't need the safeguard
        if (methodCallExpression.Object != null
            && @object!.Type.IsNullableType()
            && methodCallExpression.Method.Name != nameof(Nullable<int>.GetValueOrDefault))
        {

EF Core 9:
InMemoryExpressionTranslatingExpressionVisitor.cs line 887:

        // if object is nullable, add null safeguard before calling the function
        // we special-case Nullable<>.GetValueOrDefault, which doesn't need the safeguard,
        // and Nullable<>.ToString when the object is a nullable value type.
        if (methodCallExpression.Object != null
            && @object!.Type.IsNullableType()
            && methodCallExpression.Method.Name != nameof(Nullable<int>.GetValueOrDefault)
            && (!@object!.Type.IsNullableValueType()
                || methodCallExpression.Method.Name != nameof(Nullable<int>.ToString)))

So the new code adds explicitly a Nullable<>.ToString according to the comment, but this new code throws an exception at runtime because it cannot be called!

(For using an EF Core InMemory database in a unit test, yes I know that's not a good practice, but we inherited this Solution)

The Microsoft.EntityFrameworkCore.SqlServer package does not have this bug, it exhibits the expected behavior.

This seems a regression to me.. It is also interesting to see that the code makes an exception for the int value type, but not for any other value type.

EF Core version: 9.0
Database provider: Microsoft.EntityFrameworkCore.InMemor
Target framework: .NET 0.0)
Operating system: Windows 11 21H2
IDE: Visual Studio 2022 17.12.3

[maumar]

@wilfriedb can you share the listing of the unit test that is failing (or other form of full repro of this issue)?

I'm trying the following:

    [ConditionalFact]
    public async Task ReproDateOnly()
    {
        using var ctx = new MyContext();
        await ctx.Database.EnsureDeletedAsync();
        await ctx.Database.EnsureCreatedAsync();

        var e1 = new MyEntity { Id = 1, Do = new DateOnly(2000, 1, 1), Ndo = new DateOnly(2024, 2, 2) };
        var e2 = new MyEntity { Id = 2, Do = new DateOnly(2001, 1, 1), Ndo = null };

        ctx.MyEntities.AddRange(e1, e2);
        await ctx.SaveChangesAsync();


        var q = await ctx.MyEntities.Select(x => x.Ndo.ToString()).ToListAsync();
        var q2 = await ctx.MyEntities.Where(x => x.Ndo.ToString() != "foo").ToListAsync();
    }

    public class MyContext : DbContext
    {
        public DbSet<MyEntity> MyEntities { get; set; }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
        }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder
                    .UseInMemoryDatabase("myDateOnlyDb")
                    .LogTo(Console.WriteLine, LogLevel.Information)
                    .EnableSensitiveDataLogging();
        }
    }

    public class MyEntity
    {
        public int Id { get; set; }
        public DateOnly Do { get; set; }
        public DateOnly? Ndo { get; set; }
    }

and it works fine.

Expression tree we create here is

new QueryingEnumerable<string>(
    queryContext, 
    InMemoryShapedQueryCompilingExpressionVisitor.Table(
        queryContext: queryContext, 
        entityType: EntityType: MyEntity)
        .Select(valueBuffer => new ValueBuffer(new object[]{ ExpressionExtensions.ValueBufferTryReadValue<DateOnly?>(
            valueBuffer: valueBuffer, 
            index: 2, 
            property: Property: MyEntity.Ndo (DateOnly?)).ToString() })) // <- ToString() on Nullable<DateOnly>
        .Select(valueBuffer => new ValueBuffer(new object[]{ ExpressionExtensions.ValueBufferTryReadValue<string>(
            valueBuffer: valueBuffer, 
            index: 0, 
            property: null) })), 
    Func<QueryContext, ValueBuffer, string>, 
    AdHocMiscellaneousQueryInMemoryTest+MyContext, 
    False, 
    True
)

which is has no problems calling ToString method on DateOnly? argument.

[wilfriedb]

Hello @maumar, I'm in the process of making a minimal repo that will reproduce the issue. There are many, many expressions in this code therefore this process is not going fast . When I've finished this I will post an update here.

[wilfriedb]

Hello @maumar here is a minimal repo that reproduces the issue: https://github.com/wilfriedb/EFCoreReproduce

In this repo, the unit test will fail with an exception, as mentioned above.
When downgraded to EF Core 8, the test will succeed.

Also, with a minimal change in the file MapperProfile.cs, as indicated in the comments, the test will succeed.

Fun fact, the DateOnly field ValueDate on the PaymentModel class, on which the exception occurs, is not nullable. But when debugging in the file InMemoryExpressionTranslatingExpressionVisitor, the field (in an expression) is promoted (demoted?) to a nullable DateOnly. This is also the case in EF Core 8, but on line 888, in EF Core 9 the if statement is skipped (the condition evaluates to false), but in EF Core 8 the if statement is entered (the condition evaluates to true).

[domagojmedo]

I have the same issue, here is the 1 file repro https://github.com/domagojmedo/EfCore35299

You can just comment and uncomment line in .csproj

[domagojmedo]

Shouldn't this at least be added to breaking changes for EF 9?

[olaj]

I ran into this, doesn't really understand how it could be fixed / worked around. Do we need to downgrade? Can i ran EF Core 8 with .net 9?

[domagojmedo]

You can, that's what I did. Using [8.0.11] in test project