How to add a field with static value to MongoDB find query?

To add a field with static value to MongoDB find query, use the $literal operator with the aggregation framework. The $literal operator returns a value without parsing, making it perfect for adding constant values to query results.

Syntax

db.collection.aggregate([
    {
        $project: {
            field1: 1,
            field2: 1,
            "staticFieldName": { $literal: "staticValue" }
        }
    }
]);

Sample Data

db.fieldWithStaticValue.insertMany([
    {"Name": "Larry", "Age": 24},
    {"Name": "Chris", "Age": 23},
    {"Name": "David", "Age": 26}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5cd6554c7924bb85b3f48948"),
        ObjectId("5cd655567924bb85b3f48949"),
        ObjectId("5cd655607924bb85b3f4894a")
    ]
}

View Original Data

db.fieldWithStaticValue.find();

{ "_id": ObjectId("5cd6554c7924bb85b3f48948"), "Name": "Larry", "Age": 24 }
{ "_id": ObjectId("5cd655567924bb85b3f48949"), "Name": "Chris", "Age": 23 }
{ "_id": ObjectId("5cd655607924bb85b3f4894a"), "Name": "David", "Age": 26 }

Example: Add Static Numeric Value

db.fieldWithStaticValue.aggregate([
    {
        $project: {
            Name: 1,
            Age: 1,
            "StaticValue": { $literal: 100 }
        }
    }
]);

{ "_id": ObjectId("5cd6554c7924bb85b3f48948"), "Name": "Larry", "Age": 24, "StaticValue": 100 }
{ "_id": ObjectId("5cd655567924bb85b3f48949"), "Name": "Chris", "Age": 23, "StaticValue": 100 }
{ "_id": ObjectId("5cd655607924bb85b3f4894a"), "Name": "David", "Age": 26, "StaticValue": 100 }

Example: Add Static String Value

db.fieldWithStaticValue.aggregate([
    {
        $project: {
            Name: 1,
            Age: 1,
            "Department": { $literal: "Engineering" }
        }
    }
]);

{ "_id": ObjectId("5cd6554c7924bb85b3f48948"), "Name": "Larry", "Age": 24, "Department": "Engineering" }
{ "_id": ObjectId("5cd655567924bb85b3f48949"), "Name": "Chris", "Age": 23, "Department": "Engineering" }
{ "_id": ObjectId("5cd655607924bb85b3f4894a"), "Name": "David", "Age": 26, "Department": "Engineering" }

Key Points

• $literal can add any static value - numbers, strings, objects, or arrays.
• Use $project stage to include existing fields (1) and define new static fields.
• This approach works with the aggregation framework, not traditional find() queries.

Conclusion

The $literal operator in MongoDB's aggregation pipeline allows you to add fields with constant values to query results. Use it within $project stages to enhance documents with static data during retrieval.