** (Service) - 
** Creates sequential sequences of 'Ints' as an alternative to using BSON 'ObjectIds'.
** A Mongo Collection stores the last ID created for sequences.
** An atomic *findAndUpdate* operation both increments and returns the relevant document.
** By keeping the last IDs stored in the database it ensures the IDs are persisted between system 
** restarts and that multiple clients can generate unique IDs.
** While there is an overhead in generating new IDs, 'Int' IDs have the advantage of using less 
** space in indexes, being easier to work with in web applications and they're generally nicer to
** look at! 
const class MongoSeqs {
    ** The Mongo Collection that stores the sequences.
    const MongoColl seqColl
    ** Creates instance of 'MongoSeqs'.
    new make(MongoConnMgr connMgr, Str collName := "Seqs", Str? dbName := null) {
        this.seqColl = MongoColl(connMgr, collName, dbName ?: connMgr.mongoConnUrl.dbName)

    ** Creates instance of 'MongoSeqs' with the given collection.
    new makeWithColl(MongoColl seqColl) {
        this.seqColl = seqColl

    ** Returns the next 'Int' ID for the given sequence name. 
    Int nextId(Str seqName) {
        seqColl.findAndUpdate(["_id":seqName], ["\$inc":["lastId":1]]) {
            it->upsert = true
    ** Resets the last ID to zero.
    Void reset(Str seqName) {
        seqColl.update(["_id":seqName], ["\$set":["lastId":0]])

    ** Resets *all* the last IDs to zero.
    Void resetAll() {
        seqColl.update([:], ["\$set":["lastId":0]])

    ** Drops the 'MongoSeqs' collection.
    Void drop() {