Strategy for generating unique identifier for document in RavenDB -

say have support ticket system (simplified example). has many users , organizations. each user can member of several organizations, typical case 1 org => many users, , of them belong organization. each organization has "tag" used construct "ticket numbers" organization. lets have org called stackexchange wants tag ses.

so if open first ticket of today, want ses140407-01. next ses140407-02 , on. doesn't have 2 digits after dash.

how can make sure generated in way makes sure 100% unique across organization (no orgs have same tag)?

note: not have document id in database - guid or similar. ticket reference - kinda slug - appear in related emails etc. has unique, , prefer if didn't "waste" sequential case numbers hilo style.

is there practical way ensure unique ticket number if 2 or more people report new 1 @ same time?

edit: each organization document in ravendb, , can hold property lastissuedticketid. challenge find best way read field, generate new one, , store in way "race condition safe".

another edit: clear - intend generate ticket id in own software. looking way ask ravendb "what last ticket number", , when generate next 1 after that, "am 1 using this?" - give ticket unique case id, not related ravendb considers document id.

i use generic sequence generator written ravendb:

public class sequencegenerator {   private static readonly object lock = new object();   private readonly idocumentstore _docstore;    public sequencegenerator(idocumentstore docstore)   {     _docstore = docstore;   }    public int getnextsequencenumber(string sequencekey)   {     lock (lock)     {       using (new transactionscope(transactionscopeoption.suppress))       {         while (true)         {           try           {             var document = getdocument(sequencekey);             if (document == null)             {               putdocument(new jsondocument               {                 etag = etag.empty,                 // sending empty guid means - ensure document not exists                 metadata = new ravenjobject(),                 dataasjson = ravenjobject.fromobject(new { current = 0 }),                 key = sequencekey               });               return 0;             }              var current = document.dataasjson.value<int>("current");             current++;              document.dataasjson["current"] = current;             putdocument(document);              {               return current;             }           }           catch (concurrencyexception)           {             // expected, need retry           }         }       }     }   }    private void putdocument(jsondocument document)   {     _docstore.databasecommands.put(       document.key,       document.etag,       document.dataasjson,       document.metadata);   }    private jsondocument getdocument(string key)   {     return _docstore.databasecommands.get(key);   } } 

it generates incremental unique sequence based on sequencekey. uniqueness guaranteed raven optimistic concurrency based on etag. each sequence has own document update when generate new sequence number. also, there lock reduced db calls if several threads executing @ same moment @ same process (appdomain).

for case can use way:

var sequencekey = string.format("{0}{1:yymmdd}", yourcompanyprefix, datetime.now); var nextsequencenumber = new sequencegenerator(yourdocstore).getnextsequencenumber(sequencekey); var nextsequencekey = string.format("{0}-{1:00}", sequencekey, nextsequencenumber);