MongoDB: Updating a document with existing fields using aggregation

Question

I am new to mongodb, I am learning from some Udemy courses and I want to know how I can update a document existing field without overwriting it.

I have the following collection with these documents:

enter image description here

I want to add new warehouses in the "item":"drafts" within the stock field.

What I am trying is:

enter image description here

And giving the output it seems that is working, but when I do again db.matrices.find(), what I get is the exactly same output that in the first image.

How can I update it? I have tried also the update method, but does not do what I want to do.

Thanks!

PD: I am using linux mint, with mongo v5.0.3, and mongosh v1.1.1

Would be helpful if you can provide your sample data and expected data in text instead of images — ray
– ray, Commented Nov 1, 2021 at 1:15

Tom Slabbaert · Accepted Answer · 2021-11-01 07:49:46Z

1

You are using the aggregate pipeline, this does not update the document in the DB, it just retrieves the result. starting in Mongo version 4.2+ you can now use an aggregation pipeline ( with some limitations ) to update a document, like so:

db.collection.updateOne({
  item: "drafts"
},
[
  {
    $set: {
      stock: {
        $concatArrays: [
          "$stock",
          [
            {
              "warehouse": "A",
              qty: 20
            }
          ]
        ]
      }
    }
  }
])

Mongo Playground

I will just say that this specific update is very simple, there is no need to use an aggregation pipeline for it. a simple use of the $push operator in the update field will suffice in a "normal" update:

db.collection.updateOne({
  item: "drafts"
},
{
  $push: {
    stock: {
      "warehouse": "A",
      qty: 20
    }
  }
})

Mongo Playground

answered Nov 1, 2021 at 7:49

Tom Slabbaert

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1 Comment

Daniel Over a year ago

Ok! Thank you very much! I was searching on the web before posting this, but always pop up the "update" option without the $push operator!

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