heterogeneous bulk update in mongodb

Question

I know that we can bulk update documents in mongodb with

db.collection.update( criteria, objNew, upsert, multi )

in one db call, but it's homogeneous, i.e. all those documents impacted are following one kind of criteria. But what I'd like to do is something like

db.collection.update([{criteria1, objNew1}, {criteria2, objNew2}, ...]

, to send multiple update request which would update maybe absolutely different documents or class of documents in single db call.

What I want to do in my app is to insert/update a bunch of objects with compound primary key, if the key is already existing, update it; insert it otherwise.

Can I do all these in one combine in mongodb?

Answer 1

That's two seperate questions. To the first one; there is no MongoDB native mechanism to bulk send criteria/update pairs although technically doing that in a loop yourself is bound to be about as efficient as any native bulk support.

Checking for the existence of a document based on an embedded document (what you refer to as compound key, but in the interest of correct terminology to avoid confusion it's better to use the mongo name in this case) and insert/update depending on that existence check can be done with upsert :

document A :

{
    _id: ObjectId(...),
    key: {
        name: "Will",
        age: 20
    }
}

db.users.update({name:"Will", age:20}, {$set:{age: 21}}), true, false)

This upsert (update with insert if no document matches the criteria) will do one of two things depending on the existence of document A :

• Exists : Performs update "$set:{age:21}" on the existing document
• Doesn't exist : Create a new document with fields "name" and field "age" with values "Will" and "20" respectively (basically the criteria are copied into the new doc) and then the update is applied ($set:{age:21}). End result is a document with "name"="Will" and "age"=21.

Hope that helps

Answer 2

we are seeing some benefits of $in clause. our use case was to update the 'status' in a document for a large number number records. In our first cut, we were doing a for loop and doing updates one by 1. But then we switched to using $in clause and that made a huge improvement.