Mongo bulk find and update matched documents field in single query?

Question

I have an image gallery with meta stored in mongo. Every time the web site query matches some number of stored images i would like the documents shown counter f

Answer 1

For improved performance, take advantage of using a Bulk() API for updating the collection efficiently in bulk as you will be sending the operations to the server in batches (for example, say a batch size of 500). This gives you much better performance since you won't be sending every request to the server but just once in every 500 requests, thus making your updates more efficient and quicker.

The following demonstrates this approach, the first example uses the Bulk() API available in MongoDB versions >= 2.6 and < 3.2. It updates all the matched documents in the collection from a given array by incrementing 1 to the shown field. It assumes the array of images has the structure

var images = [
    { "_id": 1, "name": "img_1.png" },
    { "_id": 2, "name": "img_2.png" }
    { "_id": 3, "name": "img_3.png" },
    ...
    { "_id": n, "name": "img_n.png" }
]

MongoDB versions >= 2.6 and < 3.2:

var bulk = db.images.initializeUnorderedBulkOp(),
    counter = 0;

images.forEach(function (doc) {    
    bulk.find({ "_id": doc._id }).updateOne({ 
        "$inc": { "shown": 1 }
    });

    counter++;
    if (counter % 500 === 0) {
        // Execute per 500 operations
        bulk.execute(); 
        // re-initialize every 500 update statements
        bulk = db.images.initializeUnorderedBulkOp();
    }
})
// Clean up remaining queue
if (counter % 500 !== 0) { bulk.execute(); }

The next example applies to the new MongoDB version 3.2 which has since deprecated the Bulk() API and provided a newer set of apis using bulkWrite().

MongoDB version 3.2 and greater:

var ops = [];
images.forEach(function(doc) {
    ops.push({
        "updateOne": {
            "filter": { "_id": doc._id },
            "update": {
                "$inc": { "shown": 1 }
            }
        }
    });

    if (ops.length === 500 ) {
        db.images.bulkWrite(ops);
        ops = [];
    }
})

if (ops.length > 0)  
    db.images.bulkWrite(ops);