ASP .NET Web API CRUD operation using Entity Framework-Controller

CustomersController.cs

 public class CustomersController : ApiController
    {
        private CustomerAPIContext db = new CustomerAPIContext();

        // GET: api/Customers
        public IQueryable<Customer> GetCustomers()
        {
            return db.Customers;
        }

        // GET: api/Customers/5
        [ResponseType(typeof(Customer))]
        public IHttpActionResult GetCustomer(int id)
        {
            Customer customer = db.Customers.Find(id);
            if (customer == null)
            {
                return NotFound();
            }

            return Ok(customer);
        }

        // PUT: api/Customers/5
        [ResponseType(typeof(void))]
        public IHttpActionResult PutCustomer(int id, Customer customer)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            if (id != customer.CustId)
            {
                return BadRequest();
            }

            db.Entry(customer).State = EntityState.Modified;

            try
            {
                db.SaveChanges();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!CustomerExists(id))
                {
                    return NotFound();
                }
                else
                {
                    throw;
                }
            }

            return StatusCode(HttpStatusCode.NoContent);
        }

        // POST: api/Customers
        [ResponseType(typeof(Customer))]
        public IHttpActionResult PostCustomer(Customer customer)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            db.Customers.Add(customer);
            db.SaveChanges();

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

        // DELETE: api/Customers/5
        [ResponseType(typeof(Customer))]
        public IHttpActionResult DeleteCustomer(int id)
        {
            Customer customer = db.Customers.Find(id);
            if (customer == null)
            {
                return NotFound();
            }

            db.Customers.Remove(customer);
            db.SaveChanges();

            return Ok(customer);
        }

        protected override void Dispose(bool disposing)
        {
            if (disposing)
            {
                db.Dispose();
            }
            base.Dispose(disposing);
        }

        private bool CustomerExists(int id)
        {
            return db.Customers.Count(e => e.CustId == id) > 0;
        }
    }