MongoDB - Update nested document based on its current content - mongodb

Question

I have a simple collection with a document like this one:
{
_id: ObjectId('62b196e43581370007773393'),
name: 'John',
jobs: [
{
company: 'ACME',
type: 'programmer',
technologies: [
{
level: 1,
name: 'Java'
},
{
level: 3,
name: 'MongoDB'
}
]
}
]
}
I'd like to collect all technologies into a new field in the "job" sub-document for "programmers" jobs only, to achieve this effect:
(...)
jobs: [
{
it_technologies : ["Java", "MongoDB"]
(...)
}
]
(...)
The problem is that I do not know how to refer to and collect proper elements of the documents with this query:
db.runCommand({update: "employees",
updates: [
{
q: {},
u: { $set: { "jobs.$[j].it_technologies": "<how to collect all technologies in this job?>" } },
upsert: false,
multi: true,
arrayFilters: [{
$and:
[
{"j.type": "programmer"},
{"j.technologies": {$exists : true, $ne: []} }
]
}]
}
] });
Is it at all possible?
I'd be grateful for any clue!

Answer 1

Think that you need to work the update with the aggregation pipeline.
map - Iterate with the jobs array and return a new array.
1.1. $cond - Check the condition (Match the current document of jobs type and technology is not an empty array). If fulfilled, then update the document, else remains existing.
1.1.1. $mergeObjects - Merge current document with the document with it_technologies.
db.collection.update({},
[
{
$set: {
"jobs": {
$map: {
input: "$jobs",
in: {
$cond: {
if: {
$and: [
{
$eq: [
"$$this.type",
"programmer"
]
},
{
$ne: [
"$$this.technologies",
[]
]
}
]
},
then: {
$mergeObjects: [
"$$this",
{
it_technologies: "$$this.technologies.name"
}
]
},
else: "$$this"
}
}
}
}
}
}
],
{
upsert: false,
multi: true,
})
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