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…

Answer 1

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.