MongoDB: Doing $inc on multiple keys

Question

I need help incrementing value of all keys in participants without having to know name of the keys inside of it.

> db.conversations.findOne()

{
"_id" : ObjectId("4faf74b238ba278704000000"),
"participants" : {
    "4f81eab338ba27c011000001" : NumberLong(2),
    "4f78497938ba27bf11000002" : NumberLong(2)
}
}

I've tried with something like

$mongodb->conversations->update(array('_id' => new \MongoId($objectId)), array('$inc' => array('participants' => 1)));

to no avail...

Derick · Accepted Answer · 2012-05-14T13:05:55.143

2

You need to redesign your schema. It is never a good idea to have "random key names". Even though MongoDB is schemaless, it still means you need to have defined key names. You should change your schema to:

{
    "_id" : ObjectId("4faf74b238ba278704000000"),
    "participants" : [
        { _id: "4f81eab338ba27c011000001", count: NumberLong(2) },
        { _id: "4f78497938ba27bf11000002", count: NumberLong(2) }
    ]
}

Sadly, even with that, you can't update all embedded counts in one command. There is currently an open feature request for that: https://jira.mongodb.org/browse/SERVER-1243

In order to still update everything, you should:

query the document
update all the counts on the client side
store the document again

In order to prevent race conditions with that, have a look at "Compare and Swap" and following paragraphs.

edited May 14 '12 at 13:05

answered May 13 '12 at 10:40

Derick

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Ok, I've updated schema and all methods according to your example, however when doing a update by running your code above error message "can't append to array using string field name [count]" is displayed. – Sputnik May 13 '12 at 11:50
You're right. There is a Jira ticket for this: https://jira.mongodb.org/browse/SERVER-1243 Please vote for it! I've updated my answer. – Derick May 14 '12 at 13:01

score 0 · Answer 2 · edited May 23 '17 at 12:20

0

It is not possible to update all nested elements in one single move in current version of MongoDB. So I can advice to use "foreach {}".

Read realted topic: How to Update Multiple Array Elements in mongodb

I hope this feature will be implemented in next version.

edited May 23 '17 at 12:20

Community

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answered May 13 '12 at 17:50

Roman

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MongoDB: Doing $inc on multiple keys

2 Answers2