How to do HAVING COUNT in MongoDB? -


my documents this:

{     "_id": objectid("5698fcb5585b2de0120eba31"),     "id": "26125242313",     "parent_id": "26125241841",     "link_id": "10024080",     "name": "26125242313",     "author": "gigaquack",     "body": "blogging = creative writing",     "subreddit_id": "6",     "subreddit": "reddit.com",     "score": "27",     "created_utc": "2007-10-22 18:39:31" }

what i'm trying create query finds users posted 1 subreddit. did in sql using query:

select distinct author, subreddit reddit group author having count(*) = 1;

i'm trying similar in mongodb having troubles atm. managed recreate select distinct using aggregate group can't figure out how solve having count part.

this query looks like:

db.collection.aggregate(  [{"$group":      { "_id": { author: "$author", subreddit: "$subreddit" } } },     {$match:{count:1}} // part not working ])

am using $match wrong?

your query should like:

db.collection.aggregate([{   '$group': {     '_id': {'author': '$author', 'subreddit': '$subreddit'},      'count': {'$sum': 1},      'data': {'$addtoset': '$$root'}} }, {   '$match': {     'count': {'$eq': 1} }}])

where data one-length list matched document.

if want exact field, should this:

db.collection.aggregate([{   '$group': {     '_id': {'author': '$author', 'subreddit': '$subreddit'},      'count': {'$sum': 1},      'author': {'$last': '$author'}} }, {   '$match': {     'count': {'$eq': 1} }}])

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