public HttpResponseMessage Post(Pet pet) { Pet existedPet = repository.Pets.FirstOrDefault( p => p.Name == pet.Name && p.UserId == pet.UserId); if (ModelState.IsValid && existedPet == null) { repository.AddPet(pet); return(Request.CreateResponse(HttpStatusCode.OK, pet)); } else { return(Request.CreateResponse(HttpStatusCode.BadRequest, ModelState)); } }