Update nested field if a path to it isn't constant - mongodb

Question

I'm working on Django which uses MongoDB.
One of collections has the following structure:
{
"inspectionType" : {
"id" : "59a79e44d12b52042104c1e8",
"name" : "Example Name",
"inspMngrsRole" : [
{
"id" : "55937af6f3de6c004bc42862",
"type" : "inspectorManager",
"is_secret_shoper" : false
}
],
"scopes" : {
"56fcf6736389b9007a114b10" : {
"_cls" : "SomeClass",
"id" : "56fcf6736389b9007a114b10",
"name" : "Example Name",
"category" : "Example Category"
},
}
}
}
I need to update field "_cls" ("inspectionType.scopes.._cls") for all documents in the collection.
The problem is the scope_id is dynamic and unique for each scope.
Is it possible to use db.collection.update for that?
And how should the path to the field look like?
Update:
MongoDB version: 3.6.7

Answer 1

You can update using an aggregation (if you are using MongoDB version lesser than 4.2) plus an update operation or the updateMany method (if using version 4.2 or later) as follows:
# 1
var NEW_VALUE = "some new value" // the value to be updated
db.collection.aggregate( [
{
$addFields: {
"inspectionType.scopes": { $objectToArray: "$inspectionType.scopes" }
}
},
{
$addFields: {
"inspectionType.scopes.v._cls": NEW_VALUE
}
},
{
$addFields: {
"inspectionType.scopes": { $arrayToObject: "$inspectionType.scopes" }
}
}
] ).forEach( doc => db.scopes.updateOne( { _id: doc._id }, { $set: { "inspectionType.scopes": doc.inspectionType.scopes } } ) )
Starting MongoDB version 4.2 the updateMany can use an aggregation pipeline for the update operation; see Update with Aggregation Pipeline.
# 2
db.collection.updateMany(
{ },
[
{
$set: {
"inspectionType.scopes": { $objectToArray: "$inspectionType.scopes" }
}
},
{
$set: {
"inspectionType.scopes.v._cls": NEW_VALUE
}
},
{
$set: {
"inspectionType.scopes": { $arrayToObject: "$inspectionType.scopes" }
}
}
]
)