How to avoid entry of duplicate attribute?

Question

Do not allow entry of duplicate attribute value for individual attribute (user code)
 
 
 

public UserCode UpdateUserDefinedField(UserCode userCode, User user)
{
var dbCode = DbContext.UserCodes.Find(userCode.Id);
dbCode.Name = userCode.Name;
dbCode.Description = userCode.Description;
if (dbCode.UserCodeTypeId != userCode.UserCodeTypeId)
if (dbCode.UserCodeValidValues.Any(x=>x.UserCodeValues.Any()))
throw new NotSupportedException("You cannot change the attribute type because it has values in use.");
dbCode.UserCodeTypeId = userCode.UserCodeTypeId;
dbCode.IsFreeformTextValue = userCode.IsFreeformTextValue;
dbCode.IsMandatory = userCode.IsMandatory;
// Need to handle unique constraint violation
foreach (UserCodeValidValue ucvv in userCode.UserCodeValidValues)
{
UserCodeValidValue compare = dbCode.UserCodeValidValues.Where(x => x.Id == ucvv.Id).FirstOrDefault();
if (compare != null)
{
if (ucvv.Description != compare.Description || ucvv.CodeValue != compare.CodeValue)
{
compare.CodeValue = ucvv.CodeValue;
compare.Description = ucvv.Description;
UpdateWithUser(compare, user.UserId, "UpdateUserDefinedField");
}
}
else
{
ucvv.UserCode = dbCode;
AddWithUser(ucvv, user.UserId, "UpdateUserDefinedField");
}
}
UpdateWithUser(dbCode, user.UserId, "UpdateUserDefinedField");
return dbCode;
}