Combine sub-documents with missing information

In my mongoDB collection, the data structure includes:

{
    "_id" : ObjectId("..."),
    "records" : [
        ISODate("2020-04-19T00:49:18.945Z"),
        {
            "_id" : ObjectId(""),
            "date" : ISODate("2020-05-07T04:49:55.643Z"),
            "text" : "someText"
        }
    ],
}

Due to version upgrades, the content in records varies.

I am looking to aggregate records.text from all documents while disregarding any missing data. I attempted to use code shared on MongoDB: Aggregate and flatten an array field

db.collection.aggregate({$unwind : "records"},
                      {$project: {_id: 1, 'text': '$records.text'}})

However, this resulted in the following error message:

The path option to $unwind stage should be prefixed with a '$': records

I then tried to rectify the error based on instructions provided in these directions, aiming to handle empty fields:

db.collection.aggregate({$unwind : "records", includeEmpty: false},
                      {$project: {_id: 1, 'text': '$records.text'}})

Yet,d this resulted in another error:

A pipeline stage specification object must contain exactly one field.

How can I effectively aggregate values from nested arrays that may have empty elements?

javascriptmongodbaggregation-framework

Answer №1

If you want to exclude the empty records, you can utilize the $exists operator:

db.collection.aggregate([
    { $unwind: "$records" },
    { $match: { "records.text": { $exists: true } } },
    { $project: { _id: 1, text: "$records.text" }}
    {$group: {_id: "$text", count: {$sum: 1}}},
    {$sort: {count: -1}}
])

Check out this example on Mongo Playground

Answer №2

When constructing your initial query, make sure to include the '$' before 'record' as it represents a field value. The corrected version of the query would look like this:

db.collection.aggregate({$unwind : "$records"},
                      {$project: {_id: 1, 'text': '$records.text'}})

Hopefully, this adjustment resolves your issue.

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