Clash Royale CLAN TAG#URR8PPP

Issues with merging arrays of objects in MoongoDb

I trying to build an aggregation quarry in MoongoDb that will merge arrays from
2 different collection (one of the collections is of type TTL). And I facing with 2 issues that I can’t resolve.

First Issue:

I would like to merge the TakenSeats fields of my temp collations and permanent collection and set the result instead of my correct TakenSeats field, Using my aggregation in the bottom i manage to merge the arrays with the $push operator, But I cant replace the result field with the TakenSeats field that is in my permanent document.

TakenSeats

TakenSeats

$push

TakenSeats

Second Issue:

In case that I don’t have any documents in my temp collection, how can I still receive the document from the permanent one?

Sample of document in the permanent collection: (extracting data from one document)


"_id" : ObjectId("5b6b656818883ec018d1542d"),
"showsHall" : [
ObjectId("5b64cb758ad5f81a6cb7e6ae")
],
"movie" : [
ObjectId("5b6b614218883ec018d15428")
],
"takenSeats" : [

"id" : 11
,

"id" : 12

],
"showDate" : "8/14/2018",
"showStartTime" : "3:00 PM",
"showEndTime" : "5:00 PM",
"creteDate" : ISODate("2018-08-08T21:49:28.020Z"),
"__v" : 0



From the TTL collection: (extracting data from multiple documents)


"_id" : ObjectId("5b6f35023f64851baa70c61b"),
"createdAt" : ISODate("2018-08-11T19:12:02.951Z"),
"showId" : [
ObjectId("5b6b656818883ec018d1542d")
],
"takenSeats" : [

"id" : 22
,

"id" : 25

]



This is the aggregation that I used:

db.getCollection('shows').aggregate([
$match: _id: ObjectId("5b6b656818883ec018d1542d") ,

$lookup:
from: "temp",
localField: "_id",
foreignField: "showId",
as: "fromItems"

,
$unwind: "$fromItems" ,
"$project": "takenSeats": "$setUnion": ["$takenSeats", "$fromItems.takenSeats"], _id: 1, showsHall: 1, movie: 1, takenSeats: 1 , showDate: 1, showStartTime: 1, showEndTime: 1 ,
$unwind:"$takenSeats",
$group:_id: "$_id", takenSeats: $push : "$takenSeats" ,
])


Result:

[Edit]

I manage to maintain my original data with $first operator.
But now i cant resolve issue no 2 (prevent result if null), I tried to use preserveNullAndEmptyArrays
in both of the unwind stages but the result is that it pushes an empty array.
My wanted result is that it should push to a new array only if there is values to push

$first

preserveNullAndEmptyArrays

unwind

push

push

This is my aggregation :

db.getCollection('shows').aggregate([
$match: _id: ObjectId("5b6b656818883ec018d1542d") ,

$lookup:
from: "temp",
localField: "_id",
foreignField: "showId",
as: "fromItems"

,
$unwind:path:"$fromItems" ,preserveNullAndEmptyArrays:true,
"$project": "takenSeats": "$setUnion": ["$takenSeats", "$fromItems.takenSeats"], _id: 1, showsHall: 1, movie: 1, showDate: 1, showStartTime: 1, showEndTime: 1 ,
$unwind:path:"$takenSeats" ,preserveNullAndEmptyArrays:true,
,
$group:
_id: "$_id",
showsHall : $first: '$showsHall' ,
movie : $first: '$movie' ,
showDate : $first: '$showDate' ,
showStartTime : $first: '$showStartTime' ,
showEndTime : $first: '$showEndTime' ,
takenSeats: $push : "$takenSeats"


])


This is the result that i getting if there is no documents in the temp collection


"_id" : ObjectId("5b6b656818883ec018d1542d"),
"showsHall" : [
ObjectId("5b64cb758ad5f81a6cb7e6ae")
],
"movie" : [
ObjectId("5b6b614218883ec018d15428")
],
"showDate" : "8/14/2018",
"showStartTime" : "3:00 PM",
"showEndTime" : "5:00 PM",
"takenSeats" : [
null
]



$unwind

$replaceRoot: newRoot: "$takenSeats"

preserveNullAndEmptyArrays

unwind

$unwind:path:"$fromItems" ,preserveNullAndEmptyArrays:true

$unwind:"$takenSeats"

1 Answer
1

Here Please add ifNull Condition for solution 2

db.getCollection('shows').aggregate([
$match: _id: ObjectId("5b6b656818883ec018d1542d") ,

$lookup:
from: "tempShows",
localField: "_id",
foreignField: "showId",
as: "fromItems"

,
$unwind:path:"$fromItems" ,preserveNullAndEmptyArrays:true,
"$project": "takenSeats": $ifNull: [ "$setUnion": ["$takenSeats", "$fromItems.takenSeats"], '$takenSeats'] ,_id: 1, showsHall: 1, movie: 1, showDate: 1, showStartTime: 1, showEndTime: 1 ,
$unwind:path:"$takenSeats" ,preserveNullAndEmptyArrays:true,
$group:
_id: "$_id",
showsHall : $first: '$showsHall' ,
movie : $first: '$movie' ,
showDate : $first: '$showDate' ,
showStartTime : $first: '$showStartTime' ,
showEndTime : $first: '$showEndTime' ,
takenSeats: $push : "$takenSeats"


])


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