public async Task<IHttpActionResult> PostCollection(Collection collection)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            db.Collection.Add(collection);

            try
            {
                await db.SaveChangesAsync();
            }
            catch (DbUpdateException)
            {
                if (CollectionExists(collection.UserID))
                {
                    return Conflict();
                }
                else
                {
                    throw;
                }
            }

            return CreatedAtRoute("DefaultApi", new { id = collection.UserID }, collection);
        }
        public async Task<IHttpActionResult> PutCollection(int id, Collection collection)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            if (id != collection.UserID)
            {
                return BadRequest();
            }

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

            try
            {
                await db.SaveChangesAsync();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!CollectionExists(id))
                {
                    return NotFound();
                }
                else
                {
                    throw;
                }
            }

            return StatusCode(HttpStatusCode.NoContent);
        }