In MongoDB how to find documents where property is object but not Array

Question

I have collection users where each contains property gyms e.g.:

{
    "_id" : ObjectId("aaaaa"),
    "firstName" : "first",
    "lastName" : "second",
    "email" : "aaa@aaaa",
    "password" : "aaaaa",
    "gyms" : [
        {
            "name" : "aaaaaa",
            "address" : "aaaaaaaaaaaaa"
        }
    ]
}

However when I run db.users.aggregate(..) I get:

exception: Value at end of $unwind field path '$gyms' must be an Array, but is a Object

It seems that some of the users documents contain gym:{} or no gym at all rather than array. I need to find these documents, how would I do that?

EDIT:

Aggregate command I run:

db.users.aggregate({ $unwind: "$gyms" }, { $match: { "gyms.address": { $exists: true } } } )

Answer 1

Using {$type: "object"} gives you results containing documents with arrays too. So, to check for pure objects, just add an extra check to ensure that arrays are discarded, viz., obj.0.key: {$exists: false}.

In your case,

db.users.find({"gyms": {$type: "object"}, "gyms.0.name": {$exists: false}}).map(function(u) {
    // modify u.gyms to your satisfaction
    db.conversations.save(c);
})