Entity Framework Core 5 - and LinqKit.Microsoft.EntityFrameworkCore 5.0.x not working with expressions in subqueries

[rizi]

I've created a very sample solution to reproduce the issue:

I only use the LinqKit.Microsoft.EntityFrameworkCore 5.0.x package, do I need something more? The code below was working fine in EF 6 with the corresponding NuGet package, and as far as I understand when reading the readme of this repo, it should still work with EF Core 5.x, am I right?

I also tried to call .Expand() on the expression created by the FilterNames(...), but the same error occurs. I also tried to use a expression instead of the func (name => student.Name.Contains(name)) and than call .Compile() on the expression, but the same error occurs.

I got this exception: System.InvalidOperationException: 'The LINQ expression 'DbSet<Student>() .Where(s => __names_0 .Any(name => s.Name.Contains(name)))' 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.'

private static async Task Main(string[] args)
        {
            Console.WriteLine("EF Core Sample...");

            IUnityContainer container = InitUnityContainer();

           //the context is resolved by unity (ioc container)
            SchoolContext schoolContext = container.Resolve<SchoolContext>();

            Expression<Func<Student, bool>> filterNames = FilterNames(new List<string> { "MIH" });

            IReadOnlyCollection<Student> students =
                await schoolContext.Students
                    .AsExpandableEFCore()
                    .Where(filterNames)
                    .ToListAsync();
        }

        private static Expression<Func<Student, bool>> FilterNames(IReadOnlyCollection<string> names)
        {
            ExpressionStarter<Student> filterExpression = PredicateBuilder.New<Student>(true);

            if (!names.Any())
                return filterExpression;
            
            return filterExpression.And(student => names.Any(name => student.Name.Contains(name)));
        }

[sdanyliv]

This is EF Core limitation. With local collections it can do only Contains or VERY simple Any, which is not your case. Check my SO answer

[rizi]

This is EF Core limitation. With local collections it can do only Contains or VERY simple Any, which is not your case. Check my SO answer

Thx for the answer, I solved it quite similar, but I hoped there is a way to make it work. Do you know any details about the EF Core limitation? If so I would open an issue in the EF core repo.

Br

[sdanyliv]

You are not alone: https://github.com/dotnet/efcore/issues/19070