It'd be nice if there was the ability to tell Mongo on an upsert, "set this field only if a new document is created".

Example:

db.users.update(

, { $set:

, $iset:

}, true)

You could also imagine an equivalent to only set fields when updating but not inserting, although when updating there are more things you might want to do than just set ($inc, $push, etc), this may need more thought as to best approach. Perhaps $updateonly which can then contain any number of possible modifications, e.g. { $updateonly: { $inc:

, $set:

}