MongoDB Different response on different environment[Aggregate] [duplicate] - mongodb

Question

I am using a $geoNear as the first step in the aggregation framework. I need to filter out the results based on "tag" field and it works fine but I see there are 2 ways both giving different results.
Sample MongoDB Document
{
"position": [
40.80143,
-73.96095
],
"tag": "pizza"
}
I have added 2dsphere index to the "position" key
db.restaurants.createIndex( { 'position' : "2dsphere" } )
Query 1
uses $match aggregration pipeline operation to filter out the results based on "tag" key
db.restaurants.aggregate(
[
{
"$geoNear":{
"near": { type: "Point", coordinates: [ 55.8284,-4.207] },
"limit":100,
"maxDistance":10*1000,
"distanceField": "dist.calculated",
"includeLocs": "dist.location",
"distanceMultiplier":1/1000,
"spherical": true
}
},{
"$match":{"tag":"pizza"}
},
{
"$group":{"_id":null,"totalDocs":{"$sum":1}}
}
]
);
Query 2
Uses query inside the $geoNear aggregation operation to filter results based on "tag" key
db.restaurants.aggregate(
[
{
"$geoNear":{
"query" : {"tag":"pizza"}
"near": { type: "Point", coordinates: [ 55.8284,-4.207] },
"limit":100,
"maxDistance":10*1000,
"distanceField": "dist.calculated",
"includeLocs": "dist.location",
"distanceMultiplier":1/1000,
"spherical": true
}
},
{
"$group":{"_id":null,"totalDocs":{"$sum":1}}
}
]
);
The grouping option is just to get the count of documents returned by both the queries.
The totalDocs returned by both queries seem to be different.
Can someone explain me the differences between both the queries ?

Answer 1

Few assumptions:-
1. Assume there are 300 records that match based on the location.
2. Assume first set of 100 results do not have tag pizza. The rest 200 documents (101 to 300) have tag pizza
Query 1:-
There are 2 pipeline operations $geoNear and $match
The output of $geoNear pipeline operation is the input to $match
pipeline operation
$geoNear finds max of 100 results (limit we have specified) based on
the location sorted by nearest to far distance. (Note here that the
100 results retured are purely based on the location. So these 100
results do not contain any document with tag "pizza")
These 100 results are sent to the next pipeline operation $match from
where the filtering happens. But since the first set of 100 results
did not have tag pizza, the output is empty
Query 2:-
There is only 1 pipeline operation $geoNear
There is a query field included in the $geoNear pipeline operation
$geoNear finds max of 100 results (limit we have specified) based on
the location sorted by nearest to far distance and the query
tag=pizza
Now here the results from 101 to 200 are returned as output as the
query is included within the pipeline operation $geoNear. So in
simple sentence we say, find all documents with location [x,y] with
tag=pizza.
P.S : - The $group pipeline stage is added just for getting the count and hence have not written about it in the explaination

Answer 2

// If you have to apply multiple criteria to find locations then this query might helpful
const userLocations = await userModel.aggregate([
{
$geoNear: {
near: { type: "Point", coordinates: [data.lon1,data.lat1]
},//set the univercity points
spherical: true,
distanceField: "calcDistance",
// maxDistance: 2400,//25km
"distanceMultiplier": 0.001,
}
},
{ $unwind: "$location" },
{ $match: {
"location": {
$geoWithin: {
$centerSphere: [
[ 73.780553, 18.503327], 20/ 6378.1 //check the user point is present here
]
}
}
}},
])