mongodb unwind array nested inside an array of documents

Question

In MongoDB, I need to be able to unwind nested an array in a document inside an array inside the main document.

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Answer 1

In unwind stage, field should be an array field. If not array field, it treats it as array of 1 element.

From the docs:

Changed in version 3.2: $unwind stage no longer errors on non-array operands. If the operand does not resolve to an array but is not missing, null, or an empty array, $unwind treats the operand as a single element array.

---

Answer to your query:

db.response.aggregate([
    {
        $project:
        {
            "job_details.label_name":1,
            _id:0
        }
    },
    {
        $unwind:"$job_details.label_name"
    },
    {
        $group:
        {
            _id:"$job_details.label_name",
            count:{$sum:1}
        }
    }
])

Refer Shell Output