incrementing version number in a subdocument and the parent document - mongodb

Question

I am trying to add versioning levels in a document as well as its subdocuments. Heres a schema example
{
"_id" : ObjectId("59d1312a8ee6de1858933950"),
"synonyms" : [
{
"_id" : ObjectId("59d1312a8ee6de1858933954"),
"text" : [
1.0,
2.0,
3.0
],
"__v" : 1.0
},
{
"_id" : ObjectId("59d1312a8ee6de1858933953"),
"text" : [
"Foo ",
"bar ",
"Baz"
],
"__v" : 0
},
{
"_id" : ObjectId("59d1312a8ee6de1858933951"),
"text" : [
"fizz",
"bazz",
"bizz"
],
"__v" : 0
}
],
"__v" : 3.0
}
As you can see , the parent document has its own __v while each subdocument (part of the synonyms array) also has its __v . What i'm trying to accomplish is this
When updating a subdocument array - increment the version of the subdocument as well as its parent version
to that effect , i've tried the below code
db.collection.update({
'_id': ObjectId("59d1312a8ee6de1858933950"),
"synonyms._id": ObjectId("59d1312a8ee6de1858933954")
},
{$set: {'synonyms.$.text': [1,2,3]}, $inc: {'synonyms.$.__v': 1}, $inc: {"__v": 1}}
)
My parent __v is getting increment on every update but the subdocument seems to be stuck at 1.0 no matter how many updates i go through. Is there a better way?

Answer 1

If you think about the parameters that you pass to a MongoDB command as a JSON document rather than a string this makes perfect sense: Passing in the same operator twice (as in $inc at the start and later another $inc again in your example) will create a JSON document that only contains the last parameter. This would be different if you were using a string here which would actually represent a JSON document with two $inc fields.
So here's how to get it right (basically by $incing two fields as part of a single operation):
db.collection.update({
'_id': ObjectId("59d1312a8ee6de1858933950"),
"synonyms._id": ObjectId("59d1312a8ee6de1858933954")
},
{$set: {'synonyms.$.text': [1,2,3]}, $inc: {'synonyms.$.__v': 1, "__v": 1}}
)