How to sort inner array in MongoDB?

To sort inner arrays in MongoDB, use the aggregation framework with $unwind, $sort, $group, and $project stages. This approach deconstructs the array, sorts the elements, and reconstructs the sorted array.

Sample Data

db.sortInnerArrayDemo.insertOne({
    "EmployeeDetails": {
        "EmployeeAddress": {
            "EmployeeCountry": [
                {
                    "EmployeeZipCode": 1003,
                    "EmployeeStreetName": "7885 Trusel Street"
                },
                {
                    "EmployeeZipCode": 1001,
                    "EmployeeStreetName": "7390 Gonzales Drive"
                },
                {
                    "EmployeeZipCode": 1002,
                    "EmployeeStreetName": "444 N.Myres Rd."
                }
            ]
        }
    }
});

{
    "acknowledged": true,
    "insertedId": ObjectId("5c6f07d3da34711ecf87a5b8")
}

Display the document to see the original unsorted array ?

db.sortInnerArrayDemo.find().pretty();

{
    "_id": ObjectId("5c6f07d3da34711ecf87a5b8"),
    "EmployeeDetails": {
        "EmployeeAddress": {
            "EmployeeCountry": [
                {
                    "EmployeeZipCode": 1003,
                    "EmployeeStreetName": "7885 Trusel Street"
                },
                {
                    "EmployeeZipCode": 1001,
                    "EmployeeStreetName": "7390 Gonzales Drive"
                },
                {
                    "EmployeeZipCode": 1002,
                    "EmployeeStreetName": "444 N.Myres Rd."
                }
            ]
        }
    }
}

Case 1: Sort in Ascending Order

Sort the inner array by EmployeeZipCode in ascending order (1 = ascending) ?

db.sortInnerArrayDemo.aggregate([
    { $unwind: '$EmployeeDetails.EmployeeAddress.EmployeeCountry' },
    { $sort: { 'EmployeeDetails.EmployeeAddress.EmployeeCountry.EmployeeZipCode': 1 } },
    { $group: { 
        _id: '$_id', 
        'EmpCountry': { $push: '$EmployeeDetails.EmployeeAddress.EmployeeCountry' } 
    }},
    { $project: { 
        'EmployeeDetails.EmployeeAddress.EmployeeCountry': '$EmpCountry' 
    }}
]).pretty();

{
    "_id": ObjectId("5c6f07d3da34711ecf87a5b8"),
    "EmployeeDetails": {
        "EmployeeAddress": {
            "EmployeeCountry": [
                {
                    "EmployeeZipCode": 1001,
                    "EmployeeStreetName": "7390 Gonzales Drive"
                },
                {
                    "EmployeeZipCode": 1002,
                    "EmployeeStreetName": "444 N.Myres Rd."
                },
                {
                    "EmployeeZipCode": 1003,
                    "EmployeeStreetName": "7885 Trusel Street"
                }
            ]
        }
    }
}

Case 2: Sort in Descending Order

Sort the inner array by EmployeeZipCode in descending order (-1 = descending) ?

db.sortInnerArrayDemo.aggregate([
    { $unwind: '$EmployeeDetails.EmployeeAddress.EmployeeCountry' },
    { $sort: { 'EmployeeDetails.EmployeeAddress.EmployeeCountry.EmployeeZipCode': -1 } },
    { $group: { 
        _id: '$_id', 
        'EmpCountry': { $push: '$EmployeeDetails.EmployeeAddress.EmployeeCountry' } 
    }},
    { $project: { 
        'EmployeeDetails.EmployeeAddress.EmployeeCountry': '$EmpCountry' 
    }}
]).pretty();

{
    "_id": ObjectId("5c6f07d3da34711ecf87a5b8"),
    "EmployeeDetails": {
        "EmployeeAddress": {
            "EmployeeCountry": [
                {
                    "EmployeeZipCode": 1003,
                    "EmployeeStreetName": "7885 Trusel Street"
                },
                {
                    "EmployeeZipCode": 1002,
                    "EmployeeStreetName": "444 N.Myres Rd."
                },
                {
                    "EmployeeZipCode": 1001,
                    "EmployeeStreetName": "7390 Gonzales Drive"
                }
            ]
        }
    }
}

How It Works

• $unwind ? Deconstructs the array into separate documents
• $sort ? Sorts the unwound documents by the specified field
• $group ? Groups documents back by _id and pushes sorted elements into a new array
• $project ? Shapes the output to match the original document structure

Conclusion

Use MongoDB's aggregation pipeline to sort inner arrays by unwinding, sorting, grouping, and projecting. The $sort stage accepts 1 for ascending and -1 for descending order on any field within the array elements.