Mongo DB Auto Increment

MongoDB-Auto-Increment.md

Based on: https://www.tutorialspoint.com/mongodb/mongodb_autoincrement_sequence.htm

1. Create collection to store sequence numbers: db.createCollection("counters");

2. Initialize the sequence: db.counters.insert({_id:"partySeq",sequence_value:-1});

3. Define function to get next sequence value:

   function getNextSequenceValue(sequenceName){
   
      var sequenceDocument = db.counters.findAndModify({
         query:{_id: sequenceName },
         update: {$inc:{sequence_value:1}},
         new:true
      });
   
      return sequenceDocument.sequence_value;
   };
   

4. Create index on seq field: db.parties.createIndex({seq:1},{background:true, sparse:true, unique: true});

5. Enumerate the collection and assign sequence numbers:

   db.parties.find().sort({_id:1}).forEach(
   	function(p){
   		db.parties.update({_id: p._id}, {$set:{seq: getNextSequenceValue("partySeq")}})
   	}
   );