Split a document by its subdocuments in MongoDB

To split a document by its subdocuments, use $unwind in MongoDB. This operator deconstructs an array field from the input documents to output a document for each element.

Syntax

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

Sample Data

Let us create a collection with documents ?

db.demo276.insertOne({
    "Name": "Chris",
    "Subjects": ["MySQL", "MongoDB"]
});

{
    "acknowledged": true,
    "insertedId": ObjectId("5e48f953dd099650a5401a51")
}

Display all documents from a collection with the help of find() method ?

db.demo276.find().pretty();

{
    "_id": ObjectId("5e48f953dd099650a5401a51"),
    "Name": "Chris",
    "Subjects": [
        "MySQL",
        "MongoDB"
    ]
}

Example: Split Document by Subdocuments

Following is the query to split a document by its subdocuments ?

db.demo276.aggregate([
    { $unwind: "$Subjects" }
]);

{ "_id": ObjectId("5e48f953dd099650a5401a51"), "Name": "Chris", "Subjects": "MySQL" }
{ "_id": ObjectId("5e48f953dd099650a5401a51"), "Name": "Chris", "Subjects": "MongoDB" }

How It Works

The $unwind operator creates separate documents for each array element. The original document with ["MySQL", "MongoDB"] becomes two documents: one with "MySQL" and another with "MongoDB".

Conclusion

Use $unwind in an aggregation pipeline to split documents containing arrays into multiple documents. Each array element becomes a separate document with the same _id and other fields.