public IHttpActionResult PostAssignment(Assignment assignment)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            db.Assignments.Add(assignment);

            try
            {
                db.SaveChanges();
            }
            catch (DbUpdateException)
            {
                if (AssignmentExists(assignment.AssignmentID))
                {
                    return Conflict();
                }
                else
                {
                    throw;
                }
            }

            return CreatedAtRoute("DefaultApi", new { id = assignment.AssignmentID }, assignment);
        }
        public IHttpActionResult PutAssignment(int id, Assignment assignment)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            if (id != assignment.AssignmentID)
            {
                return BadRequest();
            }

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

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

            return StatusCode(HttpStatusCode.NoContent);
        }