using include on DbSet<TEntity> ef core

Question

I have several classes that all have IEnumerable of type File. but I am struggling to use include with DbSet

 public class FileRepository<T> : IFileRepository<T> where T : class
    {
        private readonly DataContext context;
        private readonly DbSet<T> table = null;

        public FileRepository(DataContext ctx)
        {
            context = ctx;
            table = context.Set<T>();
        }

        public async Task<object> GetByIdAsync(long id)
        {
            if (id > 0)
            {
                return (await table
                  .Include(x => x.Files)
                  .FirstAsync(x => x.Id == id)
                  .ConfigureAwait(false))
                  .Files.ToList();
            }
            else
            {
                return new List<File>();
            }
        }

         
    }

Severity Code Description Project File Line Suppression State Error CS1061 'T' does not contain a definition for 'Files' and no accessible extension method 'Files' accepting a first argument of type 'T' could be found (are you missing a using directive or an assembly reference?)

Answer 1

EDIT You're attempting to write code for a specific service is a generic. You need to add constraints on T.

eg T is Generic so there is no way to know there is a property. Id or Files on there, write your logic in a layer up.

public class EmployeeFiles<Employee> : IFileRepository<Employee>
{
    //... Write your logic here instead so the logic is specific to the Entity.
}

Alternatively you can have all Entity which you want to implement the file api implement an inteface

 public interface IHasFileProperties
 {
      public int Id {get; set;}
      public ICollection<File> Files { get; set; }
 }

and have the file repo:

  IFileRepository<T> where T : IHasFileProperties

Additionally from the problem you presented GetById should return T and not a list of Files, if you want to get the list of files you should make an extension on your existing repo.

Side-Note: ASP.Net-core got rid of the legacy synchronization context so you don't need to call .ConfigureAwait(false)) anymore unless you're using a library targeting the older .net 4.5 or apps with UI, see this blog by Stephen Cleary for the full detail, for a brief overview read the comments left by @IvanStoev