Insuring uniqueness of index keys

[Cliff Wiernik]

We have a file that we add various comments in and log field changes. The index key is generally unique other than some system generate items that occur to fast. Thus, I need to add a fixed ID to the key in order to guarantee uniqueness.

Inquiring as to approaches other have used. I know recently Roger discuss about ADT files and using an autoincrement field. I have some of my own thoughts and am looking for the best way to handle this. As I add records to the DBF field, an additional field would contain this number that would be guaranteed to be unique.

Cliff

[rdonnay]

You could try: UuidToChar( UuidCreate() )

This will give you a much longer string than 15.

Try this:

Code: Select all

cId := Substr(Strtran(UuidToChar( UuidCreate() ),'-',''),1,15)

[Auge_Ohr]

i use external DBF as Counter which User have to access EXCLUSIVE.

Code: Select all

// just Dummy Code
FUNCTION New_Number(cDBF)
LOCAL nNumber := -1

   DO WHILE nNumber > -10
      IF Net_Use(cDBF,;   // DBF Name
                  .T.,;   // EXCLUSIVE !!!
                 "Counter" ) // ALIAS

         nNumber := Decode(Counter->Number)
         nNumber++
         Counter->Number := Encode(nNumber) 
         SLEEP(1)
         CLOSE Counter
   EXIT
      ENDIF  
      SLEEP(100)
      nNumber--
   ENDDO
RETURN nNumber     // fail if nNumber < 0

[Cliff Wiernik]

What does the encode and decode functions do?

Isn't there alot of overhead with the file open/close exclusive requirements.

[Auge_Ohr]

What does the encode and decode functions do?

nothing special ... just be sure User do not manipulate it.

Isn't there alot of overhead with the file open/close exclusive requirements.

i do not care about overhead if it is secure.

i still do same technique with SQL in a separate field and also having a autoincrement field to compare.