a way to upsert with condition

mongo_conditional_insert.txt

// You just need to ignore dup key errors :)

// in Mongo shell: ...

> 
> var lastUpdateTime = ISODate("2013-09-10")
> var newUpdateTime = ISODate("2013-09-12")
> 
> lastUpdateTime
ISODate("2013-09-10T00:00:00Z")
> newUpdateTime
ISODate("2013-09-12T00:00:00Z")
> 
> var id = new ObjectId()
> id
ObjectId("52310502f3bf4823f81e7fc9")
>
> // collection is empty, first update will do insert:
> db.testcol.update(
... {"_id" : id, "ts" : { $lt : lastUpdateTime } },
... { $set: { ts: lastUpdateTime, data: 123 } },
... { upsert: true, multi: false }
... );
> 
> db.testcol.find()
{ "_id" : ObjectId("52310502f3bf4823f81e7fc9"), "data" : 123, "ts" : ISODate("2013-09-10T00:00:00Z") }
> 
> // try one more time to check that nothing happens (due to error):
> db.testcol.update(
... {"_id" : id, "ts" : { $lt : lastUpdateTime } },
... { $set: { ts: lastUpdateTime, data: 123 } },
... { upsert: true, multi: false }
... );
E11000 duplicate key error index: test.testcol.$_id_  dup key: { : ObjectId('52310502f3bf4823f81e7fc9') }
> 
> var tooOldToUpdate = ISODate("2013-09-09")
> 
> // update does not happen because query condition does not match
> // and mongo tries to insert with the same id (and fails with dup again):
> db.testcol.update(
... {"_id" : id, "ts" : { $lt : tooOldToUpdate } },
... { $set: { ts: tooOldToUpdate, data: 999 } },
... { upsert: true, multi: false }
... );
E11000 duplicate key error index: test.testcol.$_id_  dup key: { : ObjectId('52310502f3bf4823f81e7fc9') }
> 
> // now query cond actually matches, so update rather than insert happens which works
> // as expected:
> db.testcol.update(
... {"_id" : id, "ts" : { $lt : newUpdateTime } },
... { $set: { ts: newUpdateTime, data: 999 } },
... { upsert: true, multi: false }
... );
> 
> // check that everything worked:
> db.testcol.find()
{ "_id" : ObjectId("52310502f3bf4823f81e7fc9"), "data" : 999, "ts" : ISODate("2013-09-12T00:00:00Z") }
> 

// The only annoying part are those errors, but they are cheap and safe, so you are good.