Full Outer join in MongoDB - mongodb

Question

I want to do a Full Outer Join in MongoDB by lookup mongoDB query. Is this possible? Is a Full Outer Join supported by MongoDB by any other alternative?
[Update:]
I want to achieve result from Collection1 & Collection2 as following attachment:
Example: Result Required
In above result column there may be different arithmetic operations and will be further used in calculations.

Answer 1

You can use $unionWith (starting 4.4)
Something like this:
db.c1.aggregate([
{$set: {
mark1: "$marks"
}},
{$unionWith: {
coll: 'c2',
pipeline: [{$set: {mark2: "$marks"}}]
}},
{$group: {
_id: "$name",
result: {
$sum: "$marks"
},
mark1: {$first: {$ifNull: ["$mark1", 0]}},
mark2: {$first: {$ifNull: ["$mark2", 0]}}
}}])

Answer 2

I have named the collections as coll1 and coll2 then just use this query it will give you the required output.
db.getCollection('coll1').aggregate([
{
$facet: {
commonRecords: [{
$lookup: {
from: "coll2",
localField: 'name',
foreignField: 'name',
as: "coll2"
}
},
{
$unwind: {
path: '$coll2',
preserveNullAndEmptyArrays: true
}
}
]
}
},
{
$lookup: {
from: "coll2",
let: {
names: {
$map: {
input: '$commonRecords',
as: 'commonRecord',
in: '$$commonRecord.name'
}
}
},
pipeline: [{
$match: {
$expr: {
$eq: [{
$indexOfArray: ['$$names', '$name']
}, -1]
}
}
}, ],
as: "coll2"
}
},
{
$addFields: {
coll2: {
$map: {
input: '$coll2',
as: 'doc',
in: {
coll2: '$$doc'
}
}
}
}
},
{
$project: {
records: {
$concatArrays: ['$commonRecords', '$coll2']
}
}
},
{
$unwind: '$records'
},
{
$replaceRoot: {
newRoot: '$records'
}
},
{
$project: {
_id: 0,
name: {
$ifNull: ['$name', '$coll2.name']
},
marks1: {
$ifNull: ['$marks', 0]
},
marks2: {
$ifNull: ['$coll2.marks', 0]
}
}
},
{
$addFields: {
result: {
$add: ['$marks1', '$marks2']
}
}
}
])

Answer 3

This is a sample:
{
$lookup:
{
from: [collection to join],
local_Field: [field from the input documents],
foreign_Field: [field from the documents of the "from" collection],
as: [output field]
}
}
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