Make an array of multiple arrays in MongoDB?

To make an array of multiple arrays in MongoDB, use $unwind in the aggregation pipeline to deconstruct array fields. This operation creates separate documents for each array element, effectively flattening multiple arrays into individual elements.

Syntax

db.collection.aggregate([
    { $unwind: "$arrayField" }
]);

Sample Data

db.demo289.insertMany([
    {"Section": ["A", "B", "E"], "Name": "Chris"},
    {"Section": ["C", "D", "B"], "Name": "David"}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e4c06fcf49383b52759cbc3"),
        ObjectId("5e4c070af49383b52759cbc4")
    ]
}

View Sample Data

db.demo289.find();

{
    "_id": ObjectId("5e4c06fcf49383b52759cbc3"),
    "Section": ["A", "B", "E"],
    "Name": "Chris"
}
{
    "_id": ObjectId("5e4c070af49383b52759cbc4"),
    "Section": ["C", "D", "B"],
    "Name": "David"
}

Example: Unwind Array Elements

Use $unwind to deconstruct the Section arrays into separate documents ?

db.demo289.aggregate([
    { $unwind: "$Section" }
]);

{"_id": ObjectId("5e4c06fcf49383b52759cbc3"), "Section": "A", "Name": "Chris"}
{"_id": ObjectId("5e4c06fcf49383b52759cbc3"), "Section": "B", "Name": "Chris"}
{"_id": ObjectId("5e4c06fcf49383b52759cbc3"), "Section": "E", "Name": "Chris"}
{"_id": ObjectId("5e4c070af49383b52759cbc4"), "Section": "C", "Name": "David"}
{"_id": ObjectId("5e4c070af49383b52759cbc4"), "Section": "D", "Name": "David"}
{"_id": ObjectId("5e4c070af49383b52759cbc4"), "Section": "B", "Name": "David"}

How It Works

The $unwind operator creates a new document for each element in the specified array field. Each resulting document contains the original document's fields with the array field replaced by a single array element.

Conclusion

Use $unwind in MongoDB aggregation to deconstruct arrays into individual documents. This effectively flattens multiple arrays, creating separate documents for each array element while preserving other document fields.