Pass variables into mongo updates?

Question

Pass variables into mongo updates?

I have a mongo document that looks like this:

{ 
   "_id" : '4fb2a4809ad7324ccba1f6b8',
   "events" : { 
     "4fb2a4809ad7324ccba1f6b9" : {a:{z:1},b:{z:2},c:{z:3}},
     "4fb2a4809ad7324ccba1f610" : {a:{z:1},b:{z:2},c:{z:3}}
   } 
}

Then my server gets sent a update object.

update = { 
  _id = '4fb2a4809ad7324ccba1f6b8', 
  event_id: '4fb2a4809ad7324ccba1f610', 
  changed_data: {a:{b:3}} 
}

a.b = 3 has been created or changed. This doesn't mean a = {b:3} thus I don't want to overwrite the existing a.z = 1 already stored in the document.

How would I about writing an atomic update for these changes? The main thing I can't figure out is how to pass variables into the command to target sub-objects. (using node-mongodb-native)

Thanks for any help!

Updated document would look like:

{ 
   "_id" : '4fb2a4809ad7324ccba1f6b8',
   "events" : { 
     "4fb2a4809ad7324ccba1f6b9" : {a:{z:1},b:{z:2},c:{z:3}},
     "4fb2a4809ad7324ccba1f610" : {a:{z:1, b:3},b:{z:2},c:{z:3}}
   } 
}

javascript
node.js
mongodb

Answer 1

for (var id in update.changed_data) {
  for (var sub_id in update.changed_data[id]) {
    db.collection.update({ "_id" : update._id, "$atomic" : "true" },{ $set: {'events.' + update.event_id + '.'+ id +'.' + sub_id : update.changed_data[id][sub_id] } });
  }
}

You can also check this URL: http://www.mongodb.org/display/DOCS/Updating#Updating-ModifierOperations