Hi,

This is the standard solution that is used by SoftUni instructors, however they are using ToArray() at the beginning of the query in order to avoid a specific error with judge (even though ToArray allows no further access to nested model objects):

            var usersAndProducts = context.Users
                .ToArray() // fix for Exception InMemory Query Internal, Test 000_001
                .Where(u => u.ProductsSold.Any())
                .OrderByDescending(u => u.ProductsSold.Count)
                .Take(10)
                .Select(u => new ExportNestedUserDto
                {
                    FirstName = u.FirstName,
                    LastName = u.LastName,
                    Age = u.Age,
                    SoldProducts = new ExportNestedProductsDto
                    {
                        Count = u.ProductsSold.Count,
                        Products = u.ProductsSold.Select(ps => new ExportNestedProductDetailDto
                        {
                            Name = ps.Name,
                            Price = ps.Price,
                        }).OrderByDescending(ps => ps.Price).ToArray()
                    }
                })
                .ToArray();

            var result = new ExportUserCountDto
            {
                Count = context.Users.Count(u => u.ProductsSold.Any()),
                Users = usersAndProducts
            };

Carefull, work with using when creating instance of StringWriter in order to avoid Memory-Leak:

using var textWriter = new StringWriter();

More compact Query:

// .Where(u => u.ProductsSold.Any() && u.ProductsSold.Any(p => p.BuyerId != null))

.Where(u => u.ProductsSold.Any(p => p.BuyerId != null))