MongoCollection : Cannot update nested document

Question

I am trying to update the nested document

Document{{_id=59837be4324fb01040068109, idKey=2323, objects=[Document{{24889=Document{{key1=val1, key2=val2}}}}]}}

the json form looks like this

{
    "_id": "59837be4324fb01040068109",
    "idKey": 2323,
    "objects": [{
        "24889": {
            "key1": "val1",
            "key2": "val2"
        }
    }]
}

i tried to update as

String innerKey="24889";
mongoCollection.updateOne(eq("idKey", 2323),new Document("$set", new Document("objects."+innerKey+".key2", "val3")));

but then if i do

Document updatedDoc = mongoCollection.find(eq("idKey", 2323)).first();

i get

Document{{_id=59837be4324fb01040068109, idKey=2323, objects=[Document{{24889=Document{{key1=val1, key2=val2}}}}, null, null, null, null, null, null, null, ...

why did the object not get updated? and why do i have the nulls?

Could you please paste some valid JSON data? Your sample data appears to be more like a toString() version of your entities? — dnickless
– dnickless, Commented Aug 3, 2017 at 20:11

s7vr · Accepted Answer · 2017-08-03 21:30:25Z

2

You can't access objects by named key (24889) so if you know the position beforehand you can try

mongoCollection.updateOne(eq("idKey", 2323),new Document("$set", new Document("objects.0."+innerKey+".key2", "val3")));

Better approach would be to update your document to include keys. Something like

{
  "_id": "59837be4324fb01040068109",
  "idKey": 2323,
  "objects": [
    {
      "name": "24889",
      "value": {
        "key1": "val1",
        "key2": "val2"
      }
    }
  ]
}

and use positional operator

mongoCollection.updateOne(and(eq("idKey", 2323), eq("objects.name", innerKey)),set("objects.$.value.key2", "val3"));

`

edited Aug 3, 2017 at 21:30

answered Aug 3, 2017 at 21:23

s7vr

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4 Comments

dnickless Over a year ago

You're missing a dot after the number 0 in "objects.0"+innerKey+".key2", "val3"

AbtPst Over a year ago

thanks! that worked. just a minor tweak, i had to use Updates.set()

AbtPst Over a year ago

by the way, is there a similar way for me to get the value of an inner key? what if instead of update, i just want to get the value? I tried putting the and filter in the find() method but it always gave me teh entire document

s7vr Over a year ago

You are welcome. I should have noted that I statically imported the Updates class to use set method for your earlier comment. I don't think it is possible in first case but you can use something like for second case mongoCollection.find(and(eq("idKey", 2323), eq("objects.name", innerKey))).projection(Projections.include("objects.$")) and pick the inner value in the application code.

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