Is it possible to do a $lookup aggregation between two databases in Mongodb? It is not possible to query using lookup in two different db’s. $lookup in mongodb supports Performs a left outer join to an unsharded collection in the same database. { $lookup: { from: <collection to join>, localField: <field from the input documents>, … Read more
You need to use the $ne operator. var data = { ‘kind’: ‘tortoise’, ‘hashtag’: ‘foo’ }; Model.update( { ‘articles.hashtag’: { ‘$ne’: ‘foo’ } }, { ‘$addToSet’: { ‘articles’: data } } ) This will update the document only if there is no sub document in the “article” array with the value of hashtag equals to … Read more
You can easily identify the duplicates by running the following aggregation pipeline operation: db.collection.aggregate([ { “$group”: { “_id”: { “foreing”: “$foreing”, “value”: “$value” }, “uniqueIds”: { “$addToSet”: “$_id” }, “count”: { “$sum”: 1 } } }, { “$match”: { “count”: { “$gt”: 1 } } } ]) The $group operator in the first step is … Read more
You can try below $facet aggregation $count aggregation will always give you the counts for only single matching ($match) condition. So you need to further divide your each count into multiple section and that’s what the $facet provides by processes multiple aggregation pipelines within a single stage on the same set of input documents. db.collection.aggregate([ … Read more
MongoDB will not create an index on a collection if the index entry for an existing document exceeds the index key limit (1024 bytes). You can however create a hashed index or text index instead: db.logcollection.createIndex({“Module”:”hashed”}) or db.logcollection.createIndex({“Module”:”text”})
I am afraid that this is an ongoing problem. I had the same problem and I found a jira ticket about this: https://jira.mongodb.org/browse/SERVER-14322 It is possible that two updates come in with upsert:true, resulting in neither finding a document and both inserting new documents which conflict on unique index violations of the query predicate. The … Read more
The error is pretty much what it means as you cannot act on two things of the same “path” in the same update operation. The two operators you are using do not process sequentially as you might think they do. You can do this with as “sequential” as you can possibly get with the “bulk” … Read more
There is the db.getCollectionNames() helper method that does this for you. You can then implement your code: db.getCollectionNames().forEach(function(collname) { // find the last item in a collection var last_element = db[collname].find().sort({_id:-1}).limit(1); // check that it’s not empty if (last_element.hasNext()) { // print its timestamp printjson(last_element.next()._id.getTimestamp()); } }) You probably also want a .hasNext() check in … Read more
You don’t need to use to retrieve the document first just use the .update method with the $push operator. def update_tags(ref, new_tag): coll.update({‘ref’: ref}, {‘$push’: {‘tags’: new_tag}}) Since update is deprecated you should use the find_one_and_update or the update_one method if you are using pymongo 2.9 or newer
You can use $lookup 3.6 syntax to $project the fields inside the $lookup pipeline User.aggregate([ { “$lookup”: { “from”: “schedules”, “let”: { “id”: “$_id.phone” }, “pipeline”: [ { “$match”: { “$expr”: { “$eq”: [“$customer.phone”, “$$id”] }}}, { “$project”: { “scheduleStart”: 1, “scheduleEnd”: 1 }} ], “as”: “user_detail” }} ])