How can I increment an array element referenced by index in MongoDB?

Question

Let's say we have a collection with documents like this:

{
 _id : "some id",
 items: [
  {item: "item A", count: 5},
  {item: "item B", count: 3},
  {item: "item C", count: 9}
]
}

How can I increment the value by 1 of the third (or any other index value) element in items array?

And I want to reference not by matching value like in this question, but by index.

Why did you ask the question if you already knew the answer? Also possible duplicate stackoverflow.com/questions/16037788/… — Sarath Nair
– Sarath Nair, Commented Dec 9, 2015 at 12:45
@SarathNair it is completely okay. albeit it is a duplicate. meta.stackoverflow.com/questions/290038/… — Idos
– Idos, Commented Dec 9, 2015 at 12:46
@Idos "So I came up with a question, did my research, and found no help on S.O" the question has already been anwered here in SO — Sarath Nair
– Sarath Nair, Commented Dec 9, 2015 at 12:47
I have seen the question mentioned and I think there is enough difference to add as separate. In my case it is referenced by index, not by matching value. — tomaskazemekas
– tomaskazemekas, Commented Dec 9, 2015 at 13:08

tomaskazemekas · Accepted Answer · 2015-12-09 12:42:32Z

6

In the mongo shell it can be done this way:

db.my_collection.update(
 {_id: "some id"},
 {$inc: {"items.2.count": 1}}
)

Using PyMongo it can be done this way:

db.my_collection.update_one({"_id": "some id"},
                            {"$inc": {"items." + str(2) + ".count": 1}})

answered Dec 9, 2015 at 12:42

tomaskazemekas

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1 Comment

What if the array does not actually exist? Instead of creating [1], it creates {"0": 1}. How can I ask it to use integer keys there?