MongoDB: updating an array in array

Question

I seem to be having an issue accessing the contents of an array nested within an array in a mongodb document. I have no problems accessing the first array "groups" with a query like the following...

db.orgs.update({_id: org_id, "groups._id": group_id} , {$set: {"groups.$.name": "new_name"}});

Where I run into trouble is when I try to modify properties of an element in the array "features" nested within the "group" array.

Here is what an example document looks like

     {
        "_id" : "v5y8nggzpja5Pa7YS",
        "name" : "Example",
        "display_name" : "EX1",
        "groups" : [
            {
                "_id" : "s86CbNBdqJnQ5NWaB",
                "name" : "Group1",
                "display_name" : "G1",
                "features" : [
                    {
                        _id      : "bNQ5Bs8BWqJn6CdNa"
                        type     : "blog",
                        name     : "[blog name]"
                        owner_id : "ga5YgvP5yza7pj8nS"
                    }, 
                ]
             },
         ]
     },

And this is the query I tried to use.

db.orgs.update({_id: "v5y8nggzpja5Pa7YS", "groups._id": "qBX3KDrtMeJGvZWXZ", "groups.features._id":"bNQ5Bs8BWqJn6CdNa" }, {$set: {"groups.$.features.$.name":"New Blog Name"}});

It returns with an error message:

WriteResult({
    "nMatched" : 0,
    "nUpserted" : 0,
    "nModified" : 0,
    "writeError" : {
        "code" : 2,
        "errmsg" : "Too many positional (i.e. '$') elements found in path 'groups.$.features.$.name'"
    }
})

It seems that mongo doesn't support modifying arrays nested within arrays via the positional element?

Is there a way to modify this array without taking the entire thing out, modifying it, and then putting it back in? With multiple nesting like this is it standard practice to create a new collection? (Even though the data is only ever needed when the parent data is necessary) Should I change the document structure so that the second nested array is an object, and access it via key? (Where the key is an integer value that can act as an "_id")

groups.$.features.[KEY].name

What is considered the "correct" way to do this?

Answer 1

After some more research, it looks like the only way to modify the array within an array would be with some outside logic to find the index of the element I want to change. Doing this would require every change to have a find query to locate the index, and then an update query to modify the array. This doesn't seem like the best way.

Link to a 2010 JIRA case requesting multiple positional elements...

Since I will always know the ID of the feature, I have opted to revise my document structure.

     {
    "_id" : "v5y8nggzpja5Pa7YS",
    "name" : "Example",
    "display_name" : "EX1",
    "groups" : [
        {
            "_id" : "s86CbNBdqJnQ5NWaB",
            "name" : "Group1",
            "display_name" : "G1",
            "features" : {
               "1" : {
                       type     : "blog",
                       name     : "[blog name]"
                       owner_id : "ga5YgvP5yza7pj8nS"
               }, 
            }
         },
     ]
 },

With the new structure, changes can be made in the following manner:

db.orgs.update({_id: "v5y8nggzpja5Pa7YS", "groups._id": "s86CbNBdqJnQ5NWaB"}, {$set: {"groups.$.features.1.name":"Blog Test 1"}});