public IHttpActionResult Create(ArtistModel artist)
        {
            if (!this.ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            var newArtist = new Artist
            {
                Name = artist.Name
            };

            this.data.Artists.Add(newArtist);
            this.data.SaveChanges();

            artist.Id = newArtist.Id;

            return Ok(artist);
        }
        public IHttpActionResult Update(int id, ArtistModel artist)
        {
            if (!this.ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            var existingArtist = this.data.Artists.All().First(a => a.Id == id);
            if (existingArtist == null)
            {
                return BadRequest("Such artist does not exist!");
            }

            existingArtist.Name = artist.Name;
            this.data.SaveChanges();

            artist.Id = id;

            return Ok(artist);
        }