MongoDb: Find all (sub)documents in all collections with a particular field

Question

I need to find all Documents and Sub-Documents which contain a particular field, eg the field staffNumber might be a field in a employees collections Document as well as in a managers -Collections Sub-Documents. I want to search all Documents of all types for staffNumber fields without knowing which collection contains possible matches.

Answer 1

So let's setup some test data to start with:

> db.test.drop()
true
> db.test.insert({test:true})
WriteResult({ "nInserted" : 1 })
> db.test.insert({test:true, staffNumber: 1234})
WriteResult({ "nInserted" : 1 })
> db.test.insert({test:true, other: {staffNumber: 1234}})
WriteResult({ "nInserted" : 1 })
> db.test.insert({test:true, other1: { other2: {staffNumber: 1234}}})
WriteResult({ "nInserted" : 1 })
>

Then we can use the $where operator to run a bit of javascript:

db.test.find( { $where: function() {
   function hasProp(obj, prop) {
    for (var p in obj) {
        if (obj.hasOwnProperty(p)) {
            if (p === prop && obj[p] !== "" && obj[p] !== undefined && obj[p] !== null) {
                return obj;
            } else if (obj[p] instanceof Object && hasProp(obj[p], prop)) {
                return obj[p];
            }
        }
    }
    return null;
   }
   return hasProp(this, "staffNumber");
} } );

This will then yeild the following results:

{ "_id" : ObjectId("5a9d4146be02da4d3fc1940a"), "test" : true, "staffNumber" : 1234 }
{ "_id" : ObjectId("5a9d4153be02da4d3fc1940b"), "test" : true, "other" : { "staffNumber" : 1234 } }
{ "_id" : ObjectId("5a9d4166be02da4d3fc1940c"), "test" : true, "other1" : { "other2" : { "staffNumber" : 1234 } } }

More reading on $where - https://docs.mongodb.com/manual/reference/operator/query/where/