Mongodb merging multiple rows base on computed condition on row value - mongodb

Question

I have a sample data like this:
[
{ objectId: 1, user: 1, phones: [1, 2], emails: ['a'] },
{ objectId: 2, user: 1, phones: [1, 5], emails: ['a', 'f'] },
{ objectId: 3, user: 1, phones: [8, 9], emails: ['f', 'g'] },
{ objectId: 4, user: 1, phones: [10], emails: ['h'] },
{ objectId: 5, user: 2, phones: [1, 2, 3], emails: ['aa', 'bb', cc'] },
]
Now I need to merge all related rows into one on these conditions:
Have same user
Have at least either one common phone or email
So output something like this:
[
{ objectId: 1, user: 1, phones: [1, 2, 5, 8, 9], emails: ['a', 'f', 'g'] },
{ objectId: 4, user: 1, phones: [10], emails: ['h'] },
{ objectId: 5, user: 2, phones: [1, 2, 3], emails: ['aa', 'bb', cc'] },
]
This is what I have came up with so far:
[
{
$unwind: {
path: "$phones",
preserveNullAndEmptyArrays: true
}
},
{
$group: {
_id: {
user: "$user",
phone: "$phones"
},
objectIds: {
$addToSet: "$_id"
},
emailsList: {
$push: "$emails"
},
user: { $first: "$user" },
phones: {
$first: "$phones"
}
}
},
{
"$addFields": {
"emails": {
"$reduce": {
"input": "$emailsList",
"initialValue": [],
"in": { "$setUnion": ["$$value", "$$this"] }
}
}
}
},
{
"$project": {
"emailsList": 0
}
},
{
$unwind: {
path: "$emails",
preserveNullAndEmptyArrays: true
}
},
{
$group: {
_id: {
user: "$user",
phone: "$emails"
},
objectIdsList: {
$push: "$objectIds"
}
}
},
{
"$project": {
"mergedObjectIds": {
"$reduce": {
"input": "$objectIdsList",
"initialValue": [],
"in": { "$setUnion": ["$$value", "$$this"] }
}
}
}
}
]
And then we have a list of objectIds need to be merged in, then I will merge it all in application code. So is there anyway I can do that in aggregation framework alone, or pipe the result of this aggregate in to the next one

Answer 1

Unless I'm missing something, these are just the "sets" for each user. So simply unwind both arrays and accumulate via $addToSet for each of "phones" and "emails":
db.collection.aggregate([
{ "$unwind": "$phones" },
{ "$unwind": "$emails" },
{ "$group": {
"_id": "$user",
"phones": { "$addToSet": "$phones" },
"emails": { "$addToSet": "$emails" }
}}
])
Which returns:
{ "_id" : 2, "phones" : [ 3, 2, 1 ], "emails" : [ "cc", "bb", "aa" ] }
{ "_id" : 1, "phones" : [ 9, 1, 2, 5, 8 ], "emails" : [ "g", "f", "a" ] }
A "set" is not really considered to be "ordered", so if you expect a certain order then you need to sort elsewhere, and probably best in the client.
Any "unique" id's don't really apply here. If anything you would use a different accumulator like $min or $max, or maybe $first depending on what you want, however the only relevant details I see here is the "user" for grouping and the other accumulated "set" values.
Even though unwinding multiple arrays produces a "cartesian product" of the other values, it really does not matter when everything being pulled out is as "distinct" values anyway. This typically only matters where you need to "count" elements, and that is something your output is not looking for in the question.