public IHttpActionResult Post(int id, Listing updates) {
     updates.id = id;
     if (ModelState.IsValid) {
         updates.id = id;
         if (_repo.Update(updates)) {
             return Ok();
         }
         return InternalServerError();
     }
     return BadRequest(ModelState);
 }
 public IHttpActionResult Post(Listing newListing) {
     if (ModelState.IsValid) {
         _repo.Add(newListing);
         _repo.SaveChanges();
         if (_repo.Get(newListing.id) != null) {
             return Created("/api/listings/" + newListing.id, newListing);
         }
         return InternalServerError();
     }
     return BadRequest(ModelState);
 }