Updating nested collection inside document - MongoDB

Question

Given the following document inside Mongo:

{ 
    "_id" : ObjectId("5d5e9852b2b803bfc66e74a6"), 
    "name" : "NAME", 
    "collection1" : [ 
        { "type" : "TYPE", "collection2" : [ ] } 
    ] 
}

I would like to add elements in the collection2 attribute. I am using the mongo console.

I tried using this query:

db.mycollection.updateOne(
{"name": "NAME"}, 
{$addToSet: {"collection1.$[element].collection2" : { $each: ["a", "b", "c"]}}}, 
{arrayFilters: [{element: 0}]}
);

I also tried to use push, but with no success.

The console returns:

{ "acknowledged" : true, "matchedCount" : 1, "modifiedCount" : 0 }

Adam Harrison · Accepted Answer · 2019-08-22 18:55:33Z

The update didn't update the document because the arrayFilters clause did not match the document. Specifically, your example is filtering on an element in collection1 that is defined as 0, which does not exist.

Changing the update to filter on collection2 being an empty array should result in the update working as expected:

db.test.insert({
...     "_id" : ObjectId("5d5e9852b2b803bfc66e74a6"),
...     "name" : "NAME",
...     "collection1" : [
...         { "type" : "TYPE", "collection2" : [ ] }
...     ]
... })

db.test.update(
... { name: "NAME" },
... { "$addToSet": { collection1.$[element].collection2: { "$each" : [ "a", "b", "c" ] } } },
... { arrayFilters: [ { element.collection2: [ ] } ] }
... )

WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

db.test.find()
{ "_id" : ObjectId("5d5e9852b2b803bfc66e74a6"), "name" : "NAME", "collection1" : [ { "type" : "TYPE", "collection2" : [ "a", "b", "c" ] } ] }

Asaf Aviv · Accepted Answer · 2019-08-22 18:59:54Z

1

If you know the index of collection1 element you can omit arrayFilters and just use the index

db.mycollection.updateOne(
    { "name": "NAME" }, 
    { $addToSet: { "collection1.0.collection2": { $each: ["a", "b", "c"] }}}
);

answered Aug 22, 2019 at 18:59

Asaf Aviv

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