Algorithm generating a unique ID based on client name

Question

Following code is supposed generate a new ID (PID) for a new client based on the client name's first letter and the existing IDs in the range which are stored in a database.

For ex lets say if the new client's name is "Abc" and if last ID in the database starting from letter A, is A200. Then the new ID should be A201.

This code compiles and runs giving the desired out put but I hope this could be optimized further.

Expecting your suggestions on improving this...

private void GeneratePIDforNewPoint(string pointName)
{
 string firstLetterOfPointName; // variable to hold first letter of "point name" being passed to this method
 string lastExistingPID; // variable to hold the last PID (most recent hence largest) from the list of PIDs retrieved from the database
 int lastDigitOfExistingPID; // variable to hold last digit of the "lastPID" (ex- digit '2' from PID 'F002')
 string finalPID; // variable to hold out put (the generated new PID for the new point)...
 firstLetterOfPointName = pointName[0]; // Get the fist letter of the point name...
 List<string> pidList=_ds.GetPIDs(firstLetterOfPointName); // Calling method to get the pid list from database
 if (pidList.Count >=1) // At the end of this if block, numeric part of the new PID will be desided
 {
 pidList.Sort();
 lastExistingPID = pidList[pidList.Count - 1];
 lastDigitOfExistingPID = int.Parse(lastExistingPID[lastExistingPID.Length - 1].ToString());
 }
 else
 {
 lastDigitOfExistingPID = 0;
 }
 lastDigitOfExistingPID += 1;
 // Found digit will be converted to the pid format by attaching the starting letter and zeros to make the length.(format --> A001/ B099 / C100 etc.)
 finalPID= firstLetterOfPointName + String.Format("{0:000}", lastDigitOfExistingPID );
 _view.PID = finalPID;
}
 public List<string> GetPIDs(string firstLetterOfPointName)
 {
 string selectStatement = @"SELECT PID FROM point WHERE PID like @PID";
 List<string> pidList = new List<string>(); // List to store all retrived PIDs from the database...
 // Retrieve all existing PIDs starting with "letter" from the database
 using (SqlConnection sqlConnection = new SqlConnection(db.GetConnectionString))
 {
 using (SqlCommand sqlCommand = new SqlCommand(selectStatement, sqlConnection))
 {
 sqlCommand.Parameters.Add("@PID", SqlDbType.VarChar).Value = firstLetterOfPointName + '%';
 sqlConnection.Open();
 using (SqlDataReader dataReader = sqlCommand.ExecuteReader())
 { 
 // If reader has data, are added to the list
 while (dataReader.Read())
 {
 pidList.Add(dataReader.GetString(0).Trim());
 }
 return pidList;
 }
 }
 }
 }

• Bob Dalgleish: Create a table create table charid { id char, count long }. Search for pointName[0] as id in the table, increment count and write it back while locking the row. If pointName[0] is not in the table, add it and set the count to 1 while locking the table.

Answer 1

First, I would expect from a function named GeneratePID to return the generated ID and not to set it. (Nobody likes side-effects)

private string GeneratePIDforNewPoint(string pointName)
{
 if(pointName == null)
 return "error"; 
 var storedPIDs = _ds.GetPIDs(pointName[0]);
 var newPID = 0; 
 if(storedPIDs.Count > 0) {
 var maximumStoredPID = _ds.GetPIDs(pointName[0]).Max();
 newPID = Int32.Parse(maximumStoredPID.substring(1)) + 1;
 }
 return pointName[0] + String.Format("{0:000}", newPID); 
}

• Bob Dalgleish: Lack of side effects destroys the utility. Unless this code is single-threaded and non-reentrant, somehow you have to increment a count and/or store the new ID.
• CAD: I think when using the count, problem might be, if a record deleted accidentally in the table? Ex: Lets say it had A001,A002 and A003. Now A002 was deleted. The above code will generate A003 as new PID and would raise an error( violation of key constrain). How to avoid this?
• ceco: Okay, in that case you have to find the maximum PID. I've edited the code above.

Answer 2

It's been an old question, just thought to add an alternative to a name-with-counter solution already offered above.

ID using CRC32

ID based on data

Usually when I need an ID that is based on user's full name or some other type of data, I'd do something like this:

php example

class myUtils {
 static public function genID( $firstName, $lastName ) {
 $strDesc = $firstName . "-" . $lastName;
 return "".dechex(crc32($strDesc));
 }
}

This will return an 8-character long string representation of a 32-bit integer, for example: a072c35b

This is then simple and fast to use:

$id = myUtils::genID("First name","Last name");

This way you can generate ID that represents bunch of data grouped together, for example instead of just providing first and last name, you can add his passport number into the mix etc. to generate ID that is unique to that user.

However, if you just require a unique ID number, there's even simpler way:

Just a Unique ID

If I need to generate a unique ID that is just that - unique, I'd go for something like this:

php example

class myUtils {
 static public function uid_32bit() {
 return "".dechex(crc32(date("YdmHis").bin2hex(openssl_random_pseudo_bytes(10))));
 }
 static public function uid_64bit() {
 return self::uid_32bit().self::uid_32bit();
 }
}

This way I could get 8-character long unique string - representing 32-bit integer:

$id = myUtils::uid_32bit();

or, I could get 16-character long unique string, representing 64-bit integer value:

$id = myUtils::uid_64bit();

Main advantage of this approach is that is easily read by humans, as it contains only lowercase letters (a...f) and numbers (0...9), and can be used for instance invoice unique numbers that are shown to user, or some other client-facing output, without revealing any information about how you have structured your data in the back-end.

• RoToRa: Why do you use date($strDesc) like this? What does it do? (I believe I know why, but I'd like to hear your reasoning.)
• Siniša: Ahhh crap, that was copy-paste error. I copied function from the 2nd code snippet that uses date, but missed to remove date part. In the first code snippet It's supposed to calculate crc32 from generated string. I've edited the code snippet to fix this bug. Thanks!