mongodb: upserting: only set value if document is being inserted

Question

Considering a simple mongo document structure:

{ _id, firstTime, lastTime }

The client needs to insert a document with a known ID, or update an existing docu

Answer 1

I ran into the exact same problem and there was no simple solution for <2.4 however since 2.4 the $setOnInsert operator let's you do exactly that.

db.collection.update( ,
                      { $setOnInsert: { "firstTime":  } },
                      { upsert: true }
                    )

See the 2.4 release notes of setOnInsert for more info.