count of updated objects using node mongodb native client - node.js

Question

I have the following update MongoDB query, run in Node.js via MongoDB native client. The query works correctly - I see objects being modified in my MongoDB after I run this code:
collection.update(
{
_id : request.query.person,
},
{
$inc: {
score : 1
}
},
{ safe : true},
this /* "this" is for Step */
);
I would like to know what is the number of records that were updated in MongoDB after my query. I have seen that I can do check it by running getLastError in MongoDB, but I am not sure how to do it from Node.js using the native client.
Any hints how to do it? Is there any other way than calling getLastError?

Answer 1

The second parameter to the update callback is the count of affected docs:
collection.update(
{ _id : request.query.person },
{ $inc: { score : 1 }},
{ safe : true},
function (err, numAffected) {
...
}
);
Update for the 2.x version of the native driver:
The second parameter to the update callback is now a nested object, where the number of documents updated can be found in result.nModified. But update is now deprecated so updateOne should be used instead.
collection.updateOne(
{ _id : request.query.person },
{ $inc: { score : 1 }},
{ safe : true},
function (err, response) {
console.log(response.result.nModified);
// Also available at response.modifiedCount for updateOne, but not update
console.log(response.modifiedCount);
}
);
The documentation for the 2.x callback parameters can be found here.