public async Task<IHttpActionResult> PutCustomer(string id, Customer customer)
 {
     await collection.UpdateManyAsync(Builders<Customer>.Filter.Eq("_id", id), Builders<Customer>.Update.Set("FirstName", customer.FirstName));
     await collection.UpdateManyAsync(Builders<Customer>.Filter.Eq("_id", id), Builders<Customer>.Update.Set("LastName", customer.LastName));
     await collection.UpdateManyAsync(Builders<Customer>.Filter.Eq("_id", id), Builders<Customer>.Update.Set("YearlyIncome", customer.YearlyIncome));
     
     return StatusCode(HttpStatusCode.NoContent);
 }
        // POST: api/Customers        
        public async Task<IHttpActionResult> PostCustomer(Customer customer)
        {
            await collection.InsertOneAsync(new Customer
            {
                _id = ObjectId.GenerateNewId().ToString(),
                FirstName = customer.FirstName,
                LastName = customer.LastName,
                YearlyIncome = customer.YearlyIncome,
                DateJoined = customer.DateJoined
            });

            return CreatedAtRoute("DefaultApi", new { id = customer._id }, customer);
        }