MongoDB - How to copy rows into a newly created collection?

To copy rows from one collection to a newly created collection in MongoDB, use the aggregation pipeline with the $out operator. This operator writes the aggregation results to a specified collection.

Syntax

db.sourceCollection.aggregate([
    { $match: {} },
    { $out: "destinationCollection" }
]);

Sample Data

Let us first create a source collection with employee documents ?

db.sourceCollection.insertMany([
    {"EmployeeName": "Robert", "EmployeeSalary": 15000},
    {"EmployeeName": "David", "EmployeeSalary": 25000},
    {"EmployeeName": "Mike", "EmployeeSalary": 29000}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e0397c1f5e889d7a5199506"),
        ObjectId("5e0397c3f5e889d7a5199507"),
        ObjectId("5e0397c4f5e889d7a5199508")
    ]
}

Display the source collection documents ?

db.sourceCollection.find();

{
    "_id": ObjectId("5e0397c1f5e889d7a5199506"),
    "EmployeeName": "Robert",
    "EmployeeSalary": 15000
}
{
    "_id": ObjectId("5e0397c3f5e889d7a5199507"),
    "EmployeeName": "David",
    "EmployeeSalary": 25000
}
{
    "_id": ObjectId("5e0397c4f5e889d7a5199508"),
    "EmployeeName": "Mike",
    "EmployeeSalary": 29000
}

Method 1: Copy All Documents

Copy all documents from sourceCollection to a new destinationCollection ?

db.sourceCollection.aggregate([
    { $out: "destinationCollection" }
]);

Verify the copy operation by displaying the destination collection ?

db.destinationCollection.find();

{
    "_id": ObjectId("5e0397c1f5e889d7a5199506"),
    "EmployeeName": "Robert",
    "EmployeeSalary": 15000
}
{
    "_id": ObjectId("5e0397c3f5e889d7a5199507"),
    "EmployeeName": "David",
    "EmployeeSalary": 25000
}
{
    "_id": ObjectId("5e0397c4f5e889d7a5199508"),
    "EmployeeName": "Mike",
    "EmployeeSalary": 29000
}

Method 2: Copy with Conditions

Copy only employees with salary greater than 20000 ?

db.sourceCollection.aggregate([
    { $match: { "EmployeeSalary": { $gt: 20000 } } },
    { $out: "highSalaryEmployees" }
]);

Key Points

• The $out operator creates a new collection or replaces an existing one.
• Use $match to filter specific documents before copying.
• The destination collection will have the same document structure and _id values.

Conclusion

Use MongoDB's aggregation pipeline with the $out operator to copy documents between collections. This method efficiently transfers data while allowing filtering and transformation during the copy process.