I have a MongoDB collection, Groups. Each group has an array of members, referenced by the member's unique id. A user can be a member of many groups.
Group data looks like this:
{ _id: 1, members: ['1', '3', '5'], status: 'active' }
{ _id: 2, members: ['4', '1', '10', '11'], status: 'inactive' }
{ _id: 3, members: ['1', '2', '9'], status: 'active' }
I'm trying to extract all members of active groups as a single array of member ids, without duplication. I want to export them to a csv file using mongoexport.
I can export the ids of the relevant projects and their member lists:
mongoexport -h localhost:3001 --db mydbname --collection groups --type=csv --fields _id,members --query '{"status": "active"}' --out mongotestoutput.txt
But I can't figure out how to merge the member lists into a single array. I've been looking at Aggregation but I'm just getting lost among all the different options, I can't see which one would do what I need. Very grateful for any help.
Use aggregation with $unwind and then $out to create a new collection that looks like you need. Then export this new collection to CSV file.
db.test1.insertMany([
{ _id: 1, members: ['1', '3', '5'], status: 'active' },
{ _id: 2, members: ['4', '1', '10', '11'], status: 'inactive' },
{ _id: 3, members: ['9'], status: 'active' }
])
{_id:0} here and below is used to suppress _id field
db.test1.aggregate([
{$unwind: "$members"},
{$project:{_id:0}},
{$out:"test2"}
])
db.test2.find({},{_id:0})
{ "members" : "1", "status" : "active" }
{ "members" : "3", "status" : "active" }
{ "members" : "5", "status" : "active" }
{ "members" : "4", "status" : "inactive" }
{ "members" : "1", "status" : "inactive" }
{ "members" : "10", "status" : "inactive" }
{ "members" : "11", "status" : "inactive" }
{ "members" : "9", "status" : "active" }
Or if you need to get members by status in the array - add another $group, $addToSet stage:
db.test1.aggregate([
{$unwind: "$members"},
{$project:{_id:0}},
{ "$group": { "_id": "$status", members:{$addToSet:"$members"} } },
{$out:"test3"}
])
db.test3.find()
{ "_id" : "inactive", "members" : [ "4", "1", "10", "11" ] }
{ "_id" : "active", "members" : [ "1", "3", "5", "9" ] }
See MongoPlayground
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