public async Task <bool> ExistsAsync(int id)
        {
            var dbSet = _context.Set <TEntity>();
            var item  = await dbSet.FindAsync(id);

            if (item == null)
            {
                return(false);
            }
            else
            {
                _context.Entry(item).State = EntityState.Detached;
                return(true);
            }
        }