$near operator on a nested object list item - mongodb

Question

I have mongo db with a collection of objects with a nested object list (events) like this:
{
"_id" : ObjectId("59db84093f2fba2bf0bcfa90"),
"progressStatus" : "NOT_STARTED",
"events" : [
{
"issueDate" : ISODate("2017-10-09T00:00:00.000Z"),
"eventType" : "xyz",
"location" : {
"point" : {
"type" : "Point",
"coordinates" : [
25.6011977000001,
45.6579755
]
}
},
"cancelled" : false,
}
]
}
Trying to make a query using $near or $nearSphere operator on events.$.location:
{
"events":{
"$elemMatch":{
"eventType":"xyz",
"$and":[
{
"cancelled":false
},
{
"location.point":{
"$nearSphere":{
"$geometry":{
type:"Point",
coordinates:[
25.601198,
45.657976
]
},
"$maxDistance":20.4
}
}
}
]
}
}
}
This query gives me an error:
Error: error: {
"waitedMS" : NumberLong(0),
"ok" : 0,
"errmsg" : "geoNear must be top-level expr",
"code" : 2
}
How should it be done?

Answer 1

neptune, this happens because geospatial queries with $nearSphere uses geoNear command to fetch documents, and the geoNear expression (when the command is run) needs to be at the top level on query. In your example, it happens to be at low levels (within elemMatch), raising an error when constructing the call to geoNear.
As I understand, your 2dsphere index is on "events.location.point", right ?
So, you can make this query like:
db.sample6.find({"events": {$elemMatch: {$and: [{eventType: "xyz"},{cancelled: false}]}}, "events.location.point": {"$nearSphere": {"$geometry": {type: "Point", coordinates: [25.601198, 45.657976]}, "$maxDistance": 20.4}}})
or just
db.sample6.find({"events.eventType": "xyz", "events.cancelled": false, "events.location.point": {"$nearSphere": {"$geometry": {type: "Point", coordinates: [25.601198, 45.657976]}, "$maxDistance": 20.4}}})
This last one I think is more wise, since it has already AND behaviour, without the need of $and use. Also, if it's possible, it would be cleaner and less confusing (since these queries have a lot of brackets and parentheses) to construct the geospatial info right on "location" field (if it only contains the coordinates).