How is the Code to use for Task.FromResult<TResult> with function

Question

I want to use my function like lambda inline of my code. But i don't know how to write it.

public Task<Product> Details(string id)
        {
            return Task.FromResult(GetProduct(id));
        }

private Product GetProduct(string id)
        {
            try
            {
                var employee = db.ProductList
                    .Include(d => d.MappingProductTagList)
                    .ThenInclude(mapping => mapping.Tag)
                    .SingleOrDefault(p => p.Id == id);


                db.Entry(employee).State = EntityState.Detached; // Änderungen werden nicht geprüft.
                return employee;
            }
            catch
            {

                throw;
            }
        }

I want so use the code like this. But i get the Message "Cannot convert lambda expression to type 'Product' because it is not a delegate type"

public Task<Product> Details(string id)
        {
            return Task.FromResult<Product>(() => {
                Product employee = db.ProductList
                        .Include(d => d.MappingProductTagList)
                        .ThenInclude(mapping => mapping.Tag)
                        .SingleOrDefault(p => p.Id == id);


                db.Entry(employee).State = EntityState.Detached; // Änderungen werden nicht geprüft.
                return employee;
            });
        }

Answer 1

Task.FromResult<Product>() expects a parameter of type Product, so you can't pass a lambda expression, hence the compile error.

See: https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.task.fromresult?view=netframework-4.7.2.

Answer 2

Try the following, though I'm not entirely sure what you are trying to accomplish. You are already giving a valid example of how to use Task.FromResult right at the start. But you are asking how to do it with a lambda (I don't understand why). I'm simply assuming you want to defer the execution into an actual Task, which is what I'm demonstrating below:

public Task<Product> Details(string id)
{
    return Task.Run(() =>
    {
        Product employee = db.ProductList
                .Include(d => d.MappingProductTagList)
                .ThenInclude(mapping => mapping.Tag)
                .SingleOrDefault(p => p.Id == id);

        db.Entry(employee).State = EntityState.Detached; // Änderungen werden nicht geprüft.
        return employee;
    });
}