MongoDB how to reference object's properties in query

Question

I am attempting to run a script on my MongoDB which will set teacher_ids[] = [document.owner_id]. owner_id already exists on all of the objects in the collection. My current attempt looks like this:

db.getCollection('readings').update({ $where: "this.teacher_ids[0] != this.owner_id" }, { $set: { "teacher_ids": [this.owner_id] }}, { multi: true })

Everything almost works, except that the document looks like

doc: {
    owner_id: "some_id",
    teacher_ids: [undefined]
}

which must mean that this in the second argument of update is not referencing the document. How do I get it to set:

teacher_ids = [document.owner_id]

Example Document

{
    "_id" : ObjectId("586f07bd6a2169fdffb0563b"),
    "teacher_ids" : [],
    "owner_id" : "57c268dd6c9fd2320035e67e",
    "source" : "http://www.omfgdogs.com",
    "title" : "Test",
    "updatedAt" : ISODate("2017-01-28T07:43:46.597Z"),
    "createdAt" : ISODate("2017-01-06T02:58:05.699Z")
}

Rahul Kumar · Accepted Answer · 2017-01-28 21:13:36Z

1

I don't think in update component you can reference any other field value by this or otherwise.

It can be done through script though

db.getCollection('readings').find({ $where: "this.teacher_ids[0] != this.owner_id" }).forEach(function(x){x.teacher_ids = [x.owner_id]; db.readings.save(x)});

answered Jan 28, 2017 at 21:13

Rahul Kumar

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7 Comments

Corbfon Over a year ago

I ran this query on a sandbox collection and it set all of the arrays to [undefined], any ideas?

Rahul Kumar Over a year ago

can you add a sample document from the collection? looks like owner_id is missing in those document.

Corbfon Over a year ago

Just added an example document for you!

Corbfon Over a year ago

Ok actually, it appears that the script works fine, it just updates about 10 documents at a time before quitting. Do you have any ideas about making it stay alive until all documents from the query are updated?

Rahul Kumar Over a year ago

I tried this script with the sample document, worked fine. needed to change the name of the collection in save call in foreach function.

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