Agregate query with lookup and restriction condition in MongoDb - mongodb

Question

I have a collection myCollection
{
name : String,
members: [{status : Number, memberId : {type: Schema.Types.ObjectId, ref: 'members'}]
}
with this data :
"_id" : ObjectId("5e8b0bac041a913bc608d69d")
"members" : [
{
"status" : 4,
"_id" : ObjectId("5e8b0bac041a913bc608d69e"),
"memberId" : ObjectId("5e7dbf5b257e6b18a62f2da9"),
"date" : ISODate("2020-04-06T10:59:56.997Z")
},
{
"status" : 1,
"_id" : ObjectId("5e8b0bf2041a913bc608d6a3"),
"memberId" : ObjectId("5e7e2f048f80b46d786bfd67"),
"date" : ISODate("2020-04-06T11:01:06.463Z")
}
],
and a collection members
{
firstname : String
lastname : String
}
with this data :
[{
"_id" : ObjectId("5e7dbf5b257e6b18a62f2da9"),
"firstname" : "raed",
"lastname" : "besbes"
},
{
"_id" : ObjectId("5e7e2f048f80b46d786bfd67"),
"firstname" : "sarra",
"lastname" : "besbes"
}]
I make a query with aggregate and $lookup, to have the data populated but I want to restrict returned
data on status 1 only, this is my query and result.
how can I get data populated with only status 1 members returned ? Thank you.
query
db.getCollection('myCollection').aggregate([
{ $match: { _id: ObjectId("5e8b0bac041a913bc608d69d")}},
{
"$lookup": {
"from": "members",
"localField": "members.memberId",
"foreignField": "_id",
"as": "Members"
}
},
{
$project: {
"Members.firstname" : 1,
"Members.lastname" : 1,
"Members._id" : 1,
},
}
])
result
{
"_id" : ObjectId("5e8b0bac041a913bc608d69d"),
"Members" : [
{
"_id" : ObjectId("5e7dbf5b257e6b18a62f2da9"),
"firstname" : "raed",
"lastname" : "besbes"
},
{
"_id" : ObjectId("5e7e2f048f80b46d786bfd67"),
"firstname" : "sarra",
"lastname" : "besbes"
}
]
}

Answer 1

Option 1
Filter members before $lookup
db.myCollection.aggregate([
{
$match: {
_id: ObjectId("5e8b0bac041a913bc608d69d")
}
},
{
$addFields: {
members: {
$filter: {
input: "$members",
cond: {
$eq: [
"$$this.status",
1
]
}
}
}
}
},
{
"$lookup": {
"from": "members",
"localField": "members.memberId",
"foreignField": "_id",
"as": "Members"
}
},
{
$project: {
"Members.firstname": 1,
"Members.lastname": 1,
"Members._id": 1
}
}
])
MongoPlayground
Option 2
(Similar to 1) We flatten member array, filter only status = 1 and then perform $lookup.
db.myCollection.aggregate([
{
$match: {
_id: ObjectId("5e8b0bac041a913bc608d69d")
}
},
{
"$unwind": "$members"
},
{
$match: {
"members.status": 1
}
},
{
"$lookup": {
"from": "members",
"localField": "members.memberId",
"foreignField": "_id",
"as": "Members"
}
},
{
"$unwind": "$Members"
},
{
$group: {
_id: "$_id",
Members: {
$push: "$Members"
}
}
}
])
MongoPlayground
Option 3
We can apply filter for Member array based on filtered values for member array.
db.myCollection.aggregate([
{
$match: {
_id: ObjectId("5e8b0bac041a913bc608d69d")
}
},
{
"$lookup": {
"from": "members",
"localField": "members.memberId",
"foreignField": "_id",
"as": "Members"
}
},
{
$project: {
Members: {
$filter: {
input: "$Members",
cond: {
$in: [
"$$this._id",
{
$let: {
vars: {
input: {
$filter: {
input: "$members",
cond: {
$eq: [
"$$this.status",
1
]
}
}
}
},
in: "$$input.memberId"
}
}
]
}
}
}
}
}
])
MongoPlayground