public IHttpActionResult PutProductOwnership(DateTime id, ProductOwnership productOwnership)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            if (id != productOwnership.BuyDate)
            {
                return BadRequest();
            }

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

            try
            {
                db.SaveChanges();
            }
            catch (DbUpdateConcurrencyException)
            {
                if (!ProductOwnershipExists(id))
                {
                    return NotFound();
                }
                else
                {
                    throw;
                }
            }

            return StatusCode(HttpStatusCode.NoContent);
        }
        public IHttpActionResult GetProductOwnership(DateTime id)
        {
            ProductOwnership productOwnership = db.ProductOwnerships.Find(id);
            if (productOwnership == null)
            {
                return NotFound();
            }

            return Ok(productOwnership);
        }
        public IHttpActionResult DeleteProductOwnership(DateTime id)
        {
            ProductOwnership productOwnership = db.ProductOwnerships.Find(id);
            if (productOwnership == null)
            {
                return NotFound();
            }

            db.ProductOwnerships.Remove(productOwnership);
            db.SaveChanges();

            return Ok(productOwnership);
        }