MongoDB multiple update attributes

Question

I have a collection A that has documents in form of:

{
  _id: 12345,
  title: "title"
}

and document B in form of:

{
  _id: 12345,
  newAttribute: "newAttribute12345"
}

I want to update collection A to have documents like:

{
  _id: 12345,
  title: "title"
  newAttribute: "newAttribute12345"
}

At this time I do it with

update({_id: doc._id}, {$set: {newAttribute: doc.newAttrubute}})

, but I need to run it 10,000 in a loop for all my documents. How can I update multiple documents like these (by _id) in 1 db call or in most efficient way? (this is basically a join/bulk update attributes operation)

I use mongodb 2.6

the key thing here is updating by id - multi doesn't help me with that — taminov, Jun 03 '15 at 10:57
Actually bulk update will not be possible at this case... you have to go through loop, I think @taminov — PaulShovan, Jun 03 '15 at 11:06
Is two different collection? if yes then which criteria to set for match ? if not then how is possible to insert same `_id` value in single collection ? — Neo-coder, Jun 03 '15 at 11:11
They can be both collections, or only one of them. the match criteria is A._id = B._id if i understand you correctly — taminov, Jun 03 '15 at 11:16
@taminov mongo `_id` is unique so I will try to using two collections , If one collection with same `_id` is not possible either you should changed your matching key name other than `_id` for single collection — Neo-coder, Jun 03 '15 at 11:24
doc collection A - {id:1,prop1:1} doc collection B - {id:1,prop2:2} I want to update collection A to have {id:1,prop1:1,prop2:2} — taminov, Jun 03 '15 at 11:29

score 2 · Accepted Answer · answered Jun 03 '15 at 11:56

consider following scenario, two collections name as title and attribute.

title collection contains following documents :

[{
_id: 12345,
title: "title"
},
{
_id: 12346,
title: "title1"
}]

and attribute collection contains following document :

[{
_id: 12345,
newAttribute: "newAttribute12345"
},
{
_id: 12346,
newAttribute: "newAttribute12346"
},
{
_id: 12347,
newAttribute: "newAttribute12347"
}]

And you want to update title collection as using this criteria title._id = attribute._id use mongo bulk update with following script :

var bulk = db.title.initializeOrderedBulkOp(); 
var counter = 0;
db.attribute.find().forEach(function(data) {
    var updoc = {
      "$set": {}
    };
    var updateKey = "newAttribute";
    updoc["$set"][updateKey] = data.newAttribute;
    bulk.find({
      "_id": data._id
    }).update(updoc);
    counter++;
    // Drain and re-initialize every 1000 update statements
    if(counter % 1000 == 0) {
      bulk.execute();
      bulk = db.title.initializeOrderedBulkOp();
    }
  })
  // Add the rest in the queue
if(counter % 1000 != 0) bulk.execute();

score 0 · Answer 2 · answered Jun 03 '15 at 11:51

A possible/problematic answer is hacky join in mongo (maybe there is something better): http://tebros.com/2011/07/using-mongodb-mapreduce-to-join-2-collections/

The problem with this is that I have to swap the collections later and this requires me to know the properties of my collection

var r = function(key, values){
    var result = { prop1: null, prop2: null };
    values.forEach(function(value){
       if (result.prop1 === null && value.prop1 !== null) {
           result.prop1 = value.prop1;
       }
       if (result.prop2 === null && value.prop2 !== null) {
           result.prop2 = value.prop2;
       }
    })
    return result;
};

var m = function(){
    emit(this._id, { prop1: this.prop1, prop2: this.prop2 })
}

db.A.mapReduce(m1, r, { out: { reduce: 'C' }});
db.B.mapReduce(m1, r, { out: { reduce: 'C' }});

score 0 · Answer 3 · answered Jun 03 '15 at 11:55

0

You can use the cursor.forEach method

db.collectionA.find().forEach(function(docA){ 
    db.collectionB.find().forEach(function(docB){
        if(docA._id === docB._id){ 
            docA.newAttribute = docB.newAttribute;     
            db.collectionA.save(docA);
        }
    })
})

> db.collectionA.find()
{ "_id" : 12345, "title" : "title", "newAttribute" : "newAttribute12345" }

answered Jun 03 '15 at 11:55

styvane

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this may work on small dataset, but this query just killed my db – taminov Jun 04 '15 at 17:50

MongoDB multiple update attributes

3 Answers3