The cause of your ‘troubles’ is the second aggregation stage – { $unwind: “$address” }. It removes record for party with _id: 4 (because its address array is empty, as you mention) and produces two records for parties _id: 1 and _id: 5 (because each of them has two addresses). To prevent removing of parties … Read more
You almost answered this yourself in your tags. MongoDB has a $regex operator which allows a regular expression to be submitted as a query. So you query for strings containing “Alex” you do this: Books.find( { “authors”: { “$regex”: “Alex”, “$options”: “i” } }, function(err,docs) { } ); You can also do this: Books.find( { … Read more
You can use the $ifNull operator here. It seems the field is either not an array or not present by the given error: { “$project”: { “people”: 1, “Count”: { “$size”: { “$ifNull”: [ “$myFieldArray”, [] ] } } }} Also you might want to check for the $type in your $match in case these … Read more
Mongodb 3.4 has introduced $facet aggregation which processes multiple aggregation pipelines within a single stage on the same set of input documents. Using $facet and $group you can find documents with $limit and can get total count. You can use below aggregation in mongodb 3.4 db.collection.aggregate([ { “$facet”: { “totalData”: [ { “$match”: { }}, … Read more
Update: Starting from v4.4 there is a dedicated operator $first: { $project: { user: { $first: “$users” }, otherField: 1 }}, It’s a syntax sugar to the Original answer: You can use arrayElemAt: { $project: { user: { $arrayElemAt: [ “$users”, 0 ] }, otherField: 1 }},
You’re almost there, you need to add another $project stage to your pipeline and use the $arrayElemAt to return the single element in the array. db.users.aggregate( [ { “$project”: { “fullName”: { “$concat”: [ “$firstName”, ” “, “$lastName”] }, “country”: “$country” }}, { “$lookup”: { “from”: “countries”, “localField”: “country”, “foreignField”: “_id”, “as”: “countryInfo” }}, { … Read more
The main purpose of the aggregation framework is to ease the query of a big number of entries and generate a low number of results that hold value to you. As you have said, you can also use multiple find queries, but remember that you can not create new fields with find queries. On the … Read more
Try this: objectId.str See the doc. ObjectId() has the following attribute and methods: […] str – Returns the hexadecimal string representation of the object.
I solved the same problem just last night, this way: > db.test.aggregate({$group:{_id:{$gt:[“$field”, null]}, count:{$sum:1}}}) { “_id” : true, “count” : 2 } { “_id” : false, “count” : 2 } See http://docs.mongodb.org/manual/reference/bson-types/#bson-types-comparison-order for a full explanation of how this works. Added From comment section: To check if the value doesn’t exist or is null use … Read more
As at MongoDB 3.4, the text search feature is designed to support case-insensitive searches on text content with language-specific rules for stopwords and stemming. Stemming rules for supported languages are based on standard algorithms which generally handle common verbs and nouns but are unaware of proper nouns. There is no explicit support for partial or … Read more