Projection of one column in MongoDB?

In MongoDB, projection allows you to display only specific fields from documents instead of returning all fields. To project a single column (field), use the find() method with a projection document that specifies which fields to include or exclude.

Syntax

db.collection.find({}, {fieldToShow: 1, _id: 0});

Or exclude unwanted fields:

db.collection.find({}, {fieldToHide: 0, anotherField: 0});

Sample Data

Let us first create a collection with documents −

db.demo216.insertMany([
    {"ClientName": "John", "ClientAge": 34},
    {"ClientName": "Bob", "ClientAge": 32},
    {"ClientName": "Mike", "ClientAge": 35}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e3e351003d395bdc213470c"),
        ObjectId("5e3e351703d395bdc213470d"),
        ObjectId("5e3e351c03d395bdc213470e")
    ]
}

Display all documents from the collection −

db.demo216.find();

{ "_id": ObjectId("5e3e351003d395bdc213470c"), "ClientName": "John", "ClientAge": 34 }
{ "_id": ObjectId("5e3e351703d395bdc213470d"), "ClientName": "Bob", "ClientAge": 32 }
{ "_id": ObjectId("5e3e351c03d395bdc213470e"), "ClientName": "Mike", "ClientAge": 35 }

Method 1: Exclude Unwanted Fields

To project only the ClientName field, exclude the _id and ClientAge fields −

db.demo216.find({}, {_id: 0, "ClientAge": 0});

{ "ClientName": "John" }
{ "ClientName": "Bob" }
{ "ClientName": "Mike" }

Method 2: Include Only Desired Field

Alternatively, explicitly include only the ClientName field −

db.demo216.find({}, {"ClientName": 1, _id: 0});

{ "ClientName": "John" }
{ "ClientName": "Bob" }
{ "ClientName": "Mike" }

Key Points

• Use 1 to include fields and 0 to exclude fields in projection
• The _id field is included by default; explicitly set _id: 0 to exclude it
• Cannot mix inclusion and exclusion (except for _id)

Conclusion

MongoDB projection enables selective field retrieval using find() with a projection document. Use 0 to exclude unwanted fields or 1 to include only desired fields for efficient single-column queries.