MongoDB unwinding 2 embedded arrays separately - mongodb

Question

I have a question regarding MongoDB aggregation query which is almost similar to $unwind 2 fields separately in mongodb query.
This is the document:
{
"_id" : "1",
"details" : {
"phonenumber" : [
"1",
"2"
],
"name" : [
"a",
"b"
]
}
}
And I am trying to frame a query which will return me the following result:
{ "_id" : "1", "phonenumber" : "1", "name" : null },
{ "_id" : "1", "phonenumber" : "2", "name" : null },
{ "_id" : "1", "phonenumber" : null, "name" : "a" },
{ "_id" : "1", "phonenumber" : null, "name" : "b" }
Could someone please help me with that?
Closest solution I could figure out is by following query:
db.document.aggregate( [ { $unwind: { path: "$details.name"} }, { $unwind: { path: "$details.phonenumber" } }, { $project: { _id: 1, name: "$details.name", phonenumber: "$details.phonenumber" } } ] )
And the output from above query is:
{ "_id" : "1", "phonenumber" : "1", "name" : "a" },
{ "_id" : "1", "phonenumber" : "1", "name" : "b" },
{ "_id" : "1", "phonenumber" : "2", "name" : "a" },
{ "_id" : "1", "phonenumber" : "2", "name" : "b" }

Answer 1

With MongoDB v3.4, one of the possible solution would be,
db.document.aggregate({
'$facet': {
'phonenumber': [{
'$unwind': '$details.phonenumber'
}, {
'$project': {
phonenumber: '$details.phonenumber',
name: null
}
}],
'name': [{
'$unwind': '$details.name'
}, {
'$project': {
name: '$details.name',
phonenumber: null
}
}]
}
}, {
'$project': {
'combined': {
'$setUnion': ['$phonenumber', '$name']
}
}
}, {
'$unwind': '$combined'
}, {
'$replaceRoot': {
'newRoot': '$combined'
}
})
facet allows us to include multiple aggregation pipelines within a single stage, which is available from version 3.4

Answer 2

Alternate solution for earlier versions of mongodb,
db.document.aggregate([{
$unwind: {
path: "$details.name"
}
}, {
$group: {
_id: "$_id",
nameArr: {
$push: {
name: "$details.name",
phonenumber: {
$ifNull: ["$description", null]
}
}
},
"details": {
$first: "$details"
}
}
}, {
$unwind: "$details.phonenumber"
}, {
$group: {
_id: "$_id",
phoneArr: {
$push: {
phonenumber: "$details.phonenumber",
name: {
$ifNull: ["$description", null]
}
}
},
"nameArr": {
$first: "$nameArr"
}
}
}, {
$project: {
_id: 1,
value: {
$setUnion: ["$nameArr", "$phoneArr"]
}
}
}, {
$unwind: "$value"
}, {
$project: {
name: "$value.name",
phonenumber: "$value.phonenumber"
}
}])