Different semantics in $not $geoWithin with Polygon geometries between MongoDB 2.4 and 2.6 - mongodb

Question

I have run the following experiment, comparing how MongoDB 2.4 and MongoDB 2.6 behave regarding the $geoWithin selector combined with $not with Polygons (i.e. "outside polygon" query). I'm including the particular versions (three numbers), alghouth I guess it would happend the same with other minor versions of 2.4 and 2.6.
Two documents (A and B) are created in a given collection: A with p field set to coordinates [1, 1] and B without p field. Next, I create a 2dsphere index in p and do a query for the area outside a triangle which vertices are [0, 0], [0, 4]and [4, 0]. Note that A is inside that polygon (so it is not supposed to be got with this query).
With 2.4.9:
db.x.insert({k: "A", p: [1,1]})
db.x.insert({k: "B"})
db.x.ensureIndex({"p": "2dsphere"})
db.x.find({p: { $not: { $geoWithin: { $geometry: { type: "Polygon", coordinates: [ [ [ 0, 0 ], [ 0, 4 ], [ 4, 0 ], [ 0, 0 ] ] ] } } } }})
--> no result
Makes sense: A is not returned (as it is inside the polygon) and B is not returned (given that it doesn't have a p field).
Next, testing with 2.6.1 the same script:
db.x.insert({k: "A", p: [1,1]})
db.x.insert({k: "B"})
db.x.ensureIndex({"p": "2dsphere"})
db.x.find({p: { $not: { $geoWithin: { $geometry: { type: "Polygon", coordinates: [ [ [ 0, 0 ], [ 0, 4 ], [ 4, 0 ], [ 0, 0 ] ] ] } } } }})
-> result: B
It seems that in 2.6 semantics have changed, so when the 2dsphere-indexed field is not in a given document, that document is considered outside any possible polygon.
Changing semantics between versions is ok as long as some mechanism in the new version allows to configure behaviour in the old way. I thought that mechanism was using { "2dsphereIndexVersion" : 1 } at index creation time (based on what I read here, maybe I misunderstood that information...). However, the result (with 2.6.1 again) is the same:
db.x.insert({k: "A", p: [1,1]})
db.x.insert({k: "B"})
db.x.ensureIndex({"p": "2dsphere"}, { "2dsphereIndexVersion" : 1 })
db.x.find({p: { $not: { $geoWithin: { $geometry: { type: "Polygon", coordinates: [ [ [ 0, 0 ], [ 0, 4 ], [ 4, 0 ], [ 0, 0 ] ] ] } } } }})
-> result B
Thus, is there any way of using MongoDB 2.6 with the same semantics that MongoDB 2.4 in the sense that any document without the 2dsphere-indexed not to be returned in "outside poylgon" queries?

Answer 1

The query result in 2.6 is right - the query result in 2.4 I think I would call incorrect. Technically, your query asks for documents that do not match the $geoWithin condition. The "k" : "B" document does not match the $geoWithin condition, so it should be returned by the query. You can drop results without the p field using $exists:
db.x.find({
"p" : {
"$exists" : true,
"$not" : { "$geoWithin" : {
"$geometry" : {
"type": "Polygon",
"coordinates" : [ [ [ 0, 0 ], [ 0, 4 ], [ 4, 0 ], [ 0, 0 ] ] ]
}
} } }
})
Also note that 1) your $not query isn't actually using the geo index, as you can check with an explain, and 2) when using a 2dsphere index you should store points as GeoJSON
{
"k" : "A",
"p" : {
"type" : "Point",
"coordinates" : [1,1]
}
}
Technically it's required in MongoDB >= 2.6, and the docs say it should be an error not to use GeoJSON, but it seems to work for us.