How to update all documents in a collection with same key but different values?

Question

I have 10 documents in a collection:

>> {'_id':0, 'self':{....}} {'_id':1,'self':{....}} ........ {'_id':9,'self':{....}}

now I want to update all documents with their count, which means after the updating, the documents will look like:

>> {'_id':0, 'count':0, 'self':{....}} {'_id':1,'count':1, 'self':{....}} ........ {'_id':9,'count':9,'self':{....}}

I know there is a update({},{'$set':{}}) method but I don't know how to use this to update different values for each document. Does anyone know some fast methods to do this?

What's count supposed to be? Might well be that you should rather use an aggregation pipeline. — Markus W Mahlberg, Apr 19 '15 at 08:01
You should provide enough details about what you are asking. Here is confusion in `count`? is it same as that of `_id` field? — Vishwas, Apr 19 '15 at 08:07
Sorry for my unclear question, count is not _id, _id is a long string with letters and numbers, count is just the No. of the documents in the collection, so if I have 100 documents, then count from 0 to 99 — gladys0313, Apr 19 '15 at 08:13
Documents are unordered in collection. so you cannot do that unless it doesn't matter what the `count` value for particular document is. — styvane, Apr 19 '15 at 08:34
@Michael, thanks a lot for your comment! That's important to me — gladys0313, Apr 19 '15 at 09:03

score 0 · Answer 1 · edited Apr 19 '15 at 09:23

0

Suppose you have this data structure in database:

{

"_id" : ObjectId("4f9808648859c65d"),

"array" : [

{"text" : "foo", "value" : 11},

{"text" : "foo", "value" : 22},

{"text" : "foobar", "value" : 33}

]

}

You can update specific value using following query:

db.foo.update({"array._id" : 1}, {"$set" : {"array.$.text" : "blah"}})

I hope this will be helpful for you. Let me know.

edited Apr 19 '15 at 09:23

itzMEonTV

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answered Apr 19 '15 at 08:22

jatinkumar patel

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Hi, thanks for your answer, so you mean I need a for-loop to update all my documents, right – gladys0313 Apr 19 '15 at 08:35
I am wondering whether for-loop is efficient, do you know that? – gladys0313 Apr 19 '15 at 08:55

Dimas Kotvan · Answer 2 · 2015-04-19T14:01:50.210

0

I don't know if it's fast enough but you can write a script to do that and execute with eval.

Example:

import pymongo
from pymongo import MongoClient
client = MongoClient()
db = client.test_database
db.eval("var count = 0; db.collection_name.find().forEach(function(obj) { obj.count = count; db.collection_name.save(obj); count++ })")

edited Apr 19 '15 at 14:01

answered Apr 19 '15 at 08:22

Dimas Kotvan

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hi, thanks for your answer, but I got error: exception: ReferenceError: db_new is not defined near '_new.testcount.find().forEach(function(ob' – gladys0313 Apr 19 '15 at 08:34
I tested again and edited the answer to be more complete. Hope it helps. – Dimas Kotvan Apr 19 '15 at 14:02

score 0 · Accepted Answer · answered Apr 19 '15 at 08:43

0

for index,each in enumerate(myCollection.find({})):
    each["count"] = index
    id = each["_id"]
    each.pop("_id", None)
    collection.update({"_id":id},{"$set":each},upsert=True)

Note : documents are un-ordered in a collection as mentioned by @Michael

answered Apr 19 '15 at 08:43

Heisenberg

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Ah, thanks for your answer, so if the index value is important for each document (i.e., it makes sense if the documents are in order), then it's useless for me to assign the index value, right? – gladys0313 Apr 19 '15 at 09:02
@gladys0313 yes it is – styvane Apr 19 '15 at 09:04
@Heisenberg cool! Just want to ask more: I can use sort() to sort my documents and then the index will make sense, right – gladys0313 Apr 19 '15 at 09:09
@gladys0313 what is your goal? – styvane Apr 19 '15 at 09:14
@gladys0313: what is the significance of `count` in your application ? – Heisenberg Apr 19 '15 at 09:31
@Michael, each document in my collection represents a city grid and the whole collection is a whole city. I generate the documents from left bottom to top right of the city and I want the index to follow this order – gladys0313 Apr 19 '15 at 09:40
@Heisenberg, each document in my collection represents a city grid and the whole collection is a whole city. I generate the documents from left bottom to top right of the city and I want the index to follow this order – gladys0313 Apr 19 '15 at 09:40

score 0 · Answer 4 · answered Apr 19 '15 at 11:38

0

Assuming you are running on mongodb shell

> db.docs.find().forEach(
    function (elem) {
        db.docs.update(
            {
                _id: elem._id
            },
            {
                $set: {
                    count: elem._id
                }
            }
        );
    }
);

answered Apr 19 '15 at 11:38

Syed Mauze Rehan

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Reference http://stackoverflow.com/questions/3974985/update-mongodb-field-using-value-of-another-field http://stackoverflow.com/questions/3788256/mongodb-updating-documents-using-data-from-the-same-document/3792958#3792958 – Syed Mauze Rehan Apr 19 '15 at 11:38

How to update all documents in a collection with same key but different values?

4 Answers4