public decimal?Add(QoalaEntities context)
        {
            if (emailAlreadyExist(context, EMAIL))
            {
                throw new UserEmailExistsException();
            }

            var outParameter = new ObjectParameter("OUT_ID_USER", typeof(decimal));

            if (!(PERMISSION > 0 && PERMISSION <= 4))
            {
                PERMISSION = 1;
            }
            int ret = context.SP_INSERT_USER(NAME, PASSWORD, EMAIL, PERMISSION, ADDRESS, DISTRICT, CITY, STATE, ZIPCODE, outParameter);

            if (outParameter.Value == DBNull.Value)
            {
                ID_USER = 0m;
            }
            else
            {
                ID_USER = (Decimal)outParameter.Value;
            }
            context.Entry(this).State = EntityState.Unchanged;
            return(ID_USER);
        }