public async Task<IHttpActionResult> PutNation(int id, Nation nation)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            if (id != nation.NationID)
            {
                return BadRequest();
            }

            Group currentGroup = (nation.GroupID == nation.Group.GroupID) ? nation.Group : db.Groups.Find(nation.GroupID);
            nation.Group = currentGroup;

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

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

            return StatusCode(HttpStatusCode.NoContent);
        }
        public async Task<IHttpActionResult> PostNation(Nation nation)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }
            var isExistNation=db.Nations.Where(n => n.Name == nation.Name).FirstOrDefault();

            if (isExistNation == null)
            {
                db.Nations.Add(nation);
                await db.SaveChangesAsync();
            }
            else
            {

            }
            return CreatedAtRoute("DefaultApi", new { id = nation.NationID }, nation);
            
        }