Aggregate $filter Between Elements Matching Conditions - mongodb

Question

Data:
[
{
"_id" : ObjectId("597c48d222b29fc421e82d20"),
"Date" : "12/06/2017",
"Country" : "DEMO",
"RiderId" : "DEMO",
"VehicleId" : "DEMO",
"StartAddress" : "Colombo",
"StartLocation" : [
6.9270974,
79.8612478
],
"EndAddress" : "Kegalle,",
"EndLocation" : [
7.2476005,
80.3483415
],
"DepartureAddress" : "Dellogistics International (Pvt) Ltd, Colombo 04",
"DepartureLocation" : [
6.8824893,
79.8620031
],
"ArrivalAddress" : "Osro, Kegalle",
"ArrivalLocation" : [
7.2476005,
80.3483415
],
"IsLadiesOnly" : false,
"Notes" : "\"I'm travalleing from Bambalapitiya to Kegalle, small luggages are ok\"",
"Luggage" : 2.0,
"Detours" : 1.0,
"Route" : {
"Bounds" : {
"NorthEast" : [
7.2916216,
80.6341326
],
"SouthWest" : [
6.9270974,
79.8607731
]
},
"Legs" : [
{
"LegId" : 0.0,
"Distance" : 40033.0,
"Duration" : 4725.0,
"Price" : "240",
"StartAddress" : "Colombo",
"StartLocation" : [
6.9270974,
6.9270974
],
"EndAddress" : "Nittambuwa",
"EndLocation" : [
7.1420863,
80.1038061
],
"Ancestors" : []
},
{
"LegId" : 1.0,
"Distance" : 18008.0,
"Duration" : 1850.0,
"Price" : "480",
"StartAddress" : "Nittambuwa",
"StartLocation" : [
7.1420863,
80.1038061
],
"EndAddress" : "Warakapola",
"EndLocation" : [
7.2268383,
80.1959644
],
"Ancestors" : [
"Colombo"
]
},
{
"LegId" : 2.0,
"Distance" : 22478.0,
"Duration" : 2208.0,
"Price" : "720",
"StartAddress" : "Warakapola",
"StartLocation" : [
7.2268383,
80.1959644
],
"EndAddress" : "Kegalle",
"EndLocation" : [
7.2514362,
80.3466076
],
"Ancestors" : [
"Colombo",
"Nittambuwa"
]
}
]
},
"CreatedDate" : "2017-01-06T07:00:00.000Z",
"ModifiedDate" : "01/06/2017 12:30",
"Points" : "123"
}]
And the query is :
db.trips.aggregate([
{$match: { "Route.Legs": { $elemMatch: { "StartAddress": "Nittambuwa","Ancestors":{$nin:["Kegalle"]}} }, "Route.Legs.EndAddress":"Kegalle" }},
{ $project: {
RiderId: "$RiderId",
Legs: {
$filter: {
input: "$Route.Legs",
as: "leg",
cond: {
"$and": [
{ "$gte": [ "$$leg.LegId", <**Get the leg id by passing the start address**> ] },
{ "$lte": [ "$$leg.LegId", 3 ] }
]
}
}
}
}}
])
Basicaly inside the condition i need to query the collection and get the leg ID for comparison. i tried $where but it doesn't recognize the operator inside the condition.
Also why i cannot use $where, $nin inside the cond

Answer 1

You generally need to apply the condition by nesting another $filter within the outer $filter which looks up the matching array entry and matches the conditions. Then applying $map and $arrayElemAt to actually supply the "LegId" value for the $gte condition:
db.trips.aggregate([
{ "$match": {
"Route.Legs": {
"$elemMatch": {
"StartAddress": "Nittambuwa",
"Ancestors":{ "$nin": [ "Kegalle" ] }
}
},
"Route.Legs.EndAddress":"Kegalle"
}},
{ "$project": {
"RiderId": 1,
"Legs": {
"$filter": {
"input": "$Route.Legs",
"as": "l",
"cond": {
"$and": [
{ "$gte": [
"$$l.LegId",
{ "$arrayElemAt": [
{ "$map": {
"input": {
"$filter": {
"input": "$Route.Legs",
"as": "l",
"cond": {
"$and": [
{ "$eq": [ "$$l.StartAddress", "Nittambuwa" ] },
{ "$eq": [
{ "$size": {
"$setIntersection": [ [ "Kegalle" ], "$$l.Ancestors" ]
}},
0
]}
]
}
}
},
"as": "l",
"in": "$$l.LegId"
}},
0
]}
]},
{ "$lte": [ "$$l.LegId", 3 ] }
]
}
}
}
}}
])
You cannot really apply such things as $indexOfArray here to fetch the array index, because of the "multiple conditions" required to match the array element.
Whilst there is not a "direct" equivalence to $nin as a "logical operator" for an aggregation condition, you can use alternatives. Here I apply $setIntersection as it's probably the best to compare two "unique" arrays. The logic says when the $size of the "intersection" is 0, there there was no match. Thus meeting the same criteria as $nin.
Of course the "multiple" conditions are all wrapped by $and, since that is what it does.
The result of course filters the array items between the "LegId" value that matched the conditions, and the "end" value supplied, which is 3:
/* 1 */
{
"_id" : ObjectId("597c48d222b29fc421e82d20"),
"RiderId" : "DEMO",
"Legs" : [
{
"LegId" : 1.0,
"Distance" : 18008.0,
"Duration" : 1850.0,
"Price" : "480",
"StartAddress" : "Nittambuwa",
"StartLocation" : [
7.1420863,
80.1038061
],
"EndAddress" : "Warakapola",
"EndLocation" : [
7.2268383,
80.1959644
],
"Ancestors" : [
"Colombo"
]
},
{
"LegId" : 2.0,
"Distance" : 22478.0,
"Duration" : 2208.0,
"Price" : "720",
"StartAddress" : "Warakapola",
"StartLocation" : [
7.2268383,
80.1959644
],
"EndAddress" : "Kegalle",
"EndLocation" : [
7.2514362,
80.3466076
],
"Ancestors" : [
"Colombo",
"Nittambuwa"
]
}
]
}
All copied and pasted from the data supplied and results of the statement issued here.