mongodb - 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 field to be incremented. Using findAndModify would work OK for single document but i can't see a nice way to match multiple documents and update them all.

Is this possible with latest version of mongo? Or any recommend best practices to achieve this ?

thanks fLo

The document format is very simple

{
"name"         : "img name",
"description"  : "some more info",
"size"         : "img size in bytes",
"shown"        : "count of times the image was selected by query",
"viewed"       : "count of times the image was clicked"
}

And the query is a simple find, then use cursor to loop over results and bump the shown count using document id.. i.e.

db.images.update(
   { _id: "xxxx" },
   { $inc: { shown: 1 } }
)

But i would prefer not to get 100 documents then have to loop over each to update individually. Was hoping to perform find and update in single query.

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);