public async Task<IHttpActionResult> PutProduct(Product entity)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            _dbContext.ApplyChanges(entity);

            try
            {
                await _dbContext.SaveChangesAsync();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!_dbContext.Products.Any(e => e.ProductId == entity.ProductId))
                {
                    return Conflict();
                }
                throw;
            }

            await _dbContext.LoadRelatedEntitiesAsync(entity);
            entity.AcceptChanges();
            return Ok(entity);
        }
        public async Task<IHttpActionResult> PostProduct(Product entity)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            entity.TrackingState = TrackingState.Added;
            _dbContext.ApplyChanges(entity);


            try
            {
                await _dbContext.SaveChangesAsync();
            }
            catch (DbUpdateException)
            {
                if (_dbContext.Products.Any(e => e.ProductId == entity.ProductId))
                {
                    return Conflict();
                }
                throw;
            }

            await _dbContext.LoadRelatedEntitiesAsync(entity);
            entity.AcceptChanges();
            return CreatedAtRoute("DefaultApi", new { id = entity.ProductId }, entity);
        }