SkipWhile: Processing of the LINQ expression failed

[Neme12]

Steps to reproduce

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

namespace ConsoleApp3
{
    public sealed class Record
    {
        public int Id { get; set; }
        public DateTime Time { get; set; }
    }

    public sealed class ApplicationDbContext : DbContext
    {
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            base.OnConfiguring(optionsBuilder);
            optionsBuilder.UseSqlServer("Server=(localdb)\\mssqllocaldb;Database=aspnet-WebApplication-6E483A89-BEE6-4A76-96CC-CEB276E5E112;Trusted_Connection=True;MultipleActiveResultSets=true");
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
        }

        public DbSet<Record> Records { get; set; }
    }

    public static class Program
    {
        public static void Main()
        {
            using (var context = new ApplicationDbContext())
            {
                context.Database.EnsureDeleted();
                context.Database.EnsureCreated();

                context.Records.Add(new Record { Time = new DateTime(2019, 11, 16) });
                context.Records.Add(new Record { Time = new DateTime(2019, 11, 17) });
                context.Records.Add(new Record { Time = new DateTime(2019, 11, 18) });
                context.SaveChanges();
            }

            using (var context = new ApplicationDbContext())
            {
                var record = context.Records.Find(2);

                var previousRecord = context.Records
                    .OrderByDescending(r => r.Time)
                    .ThenByDescending(r => r.Id)
                    .SkipWhile(r => r.Id != record.Id)
                    .Skip(1)
                    .FirstOrDefault();
            }
        }
    }
}

After running this, I get this exception:

System.InvalidOperationException: 'Processing of the LINQ expression 'SkipWhile(
source: ThenByDescending<Record, int>(
source: OrderByDescending<Record, DateTime>(
source: DbSet,
keySelector: (r) => r.Time),
keySelector: (r) => r.Id),
predicate: (r) => r.Id != (Unhandled parameter: __record_Id_0))' by 'NavigationExpandingExpressionVisitor' failed. This may indicate either a bug or a limitation in EF Core. See https://go.microsoft.com/fwlink/?linkid=2101433 for more detailed information.'

I assume this is because SkipWhile isn't actually implemented (looking at #14104), but the error message is really cryptic. It's an InvalidOperationException simply saying that processing the expression failed and mentions that it might be a bug in EF Core.

Running the same code under EF Core 2.2, I get:

System.NotSupportedException: 'Could not parse expression 'value(Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1[ConsoleApp3.Record]).OrderByDescending(r => r.Time).ThenByDescending(r => r.Id).SkipWhile(r => (r.Id != __record_Id_0))': This overload of the method 'System.Linq.Queryable.SkipWhile' is currently not supported.'

which is much clearer - it tells me that SkipWhile isn't supported. This is at the very least a regression in the readability of this error message.

Further technical details

EF Core version: 3.0.0
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET Core 3.0
Operating system: Windows 10 Version 1903
IDE: Visual Studio 16.4.0 Preview 5.0

[ajcvickers]

Putting this on the backlog to throw a better exception.

[smitpatel]

Probably the exception is already improved.

[maumar]

current exception:

The LINQ expression 'DbSet<Customer>()
        .OrderBy(c => c.CustomerID)
        .SkipWhile(c => c.CustomerID != "Foo")' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList', or 'ToListAsync'. See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.
  Stack Trace: 

[Neme12]

@maumar But that exception message still doesn't tell me why it couldn't be translated. It's basically the same as the original exception message with the query inside it. But I feel the the exception should say that SkipWhile isn't supported. This might be a trivial example but when I get this exception in a long query, I'm completely lost as to what could be wrong and which part or which combination of features EF Core doesn't support.

[Neme12]

The exception message in EF Core 2.2 is still much better because it tells me that it's the SkipWhile method that isn't supported/implemented.

[smitpatel]

When query translation fails, if there is anything specific we indicate the reason (like using not mapped property). Otherwise it is the last query operator in exception message which fails the whole query. We will consider improving it in future if there is enough user feedback that it is not clear.