mongodb positional operator error

Gor picture Gor · Jun 3, 2016 · Viewed 24.5k times · Source

I have objects like this

{
    "_id" : ObjectId("5742be02289512cf98bf63e3"),
    "name" : "test1",
    "name" : "test1",
    "attributes" : [ 
        {
            "name" : "x",
            "color" : "0xd79c9c",
            "_id" : ObjectId("5742be02289512cf98bf63e8")
        }, 
        {
            "name" : "y",
            "color" : "0xd79c9c",
            "_id" : ObjectId("5742be02289512cf98bf63e7")
        }, 
        {
            "name" : "z",
            "color" : "0xd79c9c",
            "_id" : ObjectId("5742be02289512cf98bf63e6")
        }
    ],
    "__v" : 6
}

And I want to update all documents, and set for each attribute new field. So I want to run single query, to update all documents at once. I think, this query will do it

db.spaces.update({}, { $set: { "attributes.0.weight": 2 } }, {multi: true})

But when I run this query, I get an error.

"code" : 16837,
"errmsg" : "The positional operator did not find the match needed from the query. Unexpanded update: attributes.$.weight"

So I cant understand why. Please help

Answer

chridam picture chridam · Jun 3, 2016

You need to include the array field as part of the query document in order to use the positional operator.

For example, if you want to update the first array element i.e. with { "attributes.name": "x" } then you could follow the pattern:

db.spaces.update(
   { "attributes.name": "x" }, // <-- the array field must appear as part of the query document.
   { "$set": { "attributes.$.weight": 2 } },
   { "multi": true }
)

For the newer MongoDB versions 3.2.X, you could use the updateMany() method to update multiple documents within the collection based on the filter above.