public async Task Put(int id, [FromBody] TankReadingsEntry value)
        {
            try {
                var old = await _db.TankReadings.FindAsync(id);

                _db.Entry(old).CurrentValues.SetValues(value);
                await _db.SaveChangesAsync();
            }
            catch (Exception error)
            {
                throw new Exception(error.Message);
            }
        }
        public async Task <IActionResult> Post([FromBody] TankReadingsEntry value)
        {
            if (ModelState.IsValid)
            {
                await _db.TankReadings.AddAsync(value);

                await _db.SaveChangesAsync();

                return(Ok("Ok"));
            }
            else
            {
                return(new BadRequestObjectResult("Not Found"));
            }
        }