How to retrieve a value from MongoDB by its key name?

To retrieve a value from MongoDB by its key name, use projection in the find() method to specify which fields to return while excluding others.

Syntax

db.collectionName.find({}, {"fieldName": 1});

Set the field value to 1 to include it, or 0 to exclude it from the result.

Sample Data

db.retrieveValueFromAKeyDemo.insertMany([
    {"CustomerName": "Larry", "CustomerAge": 21, "CustomerCountryName": "US"},
    {"CustomerName": "Chris", "CustomerAge": 24, "CustomerCountryName": "AUS"},
    {"CustomerName": "Mike", "CustomerAge": 26, "CustomerCountryName": "UK"}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5c9163b5a56efcc0f9e69048"),
        ObjectId("5c9163c4a56efcc0f9e69049"),
        ObjectId("5c9163d3a56efcc0f9e6904a")
    ]
}

Example: Retrieve Specific Field

To retrieve only the CustomerCountryName field from all documents ?

db.retrieveValueFromAKeyDemo.find({}, {"CustomerCountryName": 1});

{
    "_id": ObjectId("5c9163b5a56efcc0f9e69048"),
    "CustomerCountryName": "US"
}
{
    "_id": ObjectId("5c9163c4a56efcc0f9e69049"),
    "CustomerCountryName": "AUS"
}
{
    "_id": ObjectId("5c9163d3a56efcc0f9e6904a"),
    "CustomerCountryName": "UK"
}

Exclude _id Field

To retrieve only the field value without the _id field ?

db.retrieveValueFromAKeyDemo.find({}, {"CustomerCountryName": 1, "_id": 0});

{
    "CustomerCountryName": "US"
}
{
    "CustomerCountryName": "AUS"
}
{
    "CustomerCountryName": "UK"
}

Key Points

• Use 1 to include fields and 0 to exclude fields in projection
• The _id field is included by default unless explicitly excluded with "_id": 0
• You cannot mix inclusion and exclusion in the same projection (except for _id)

Conclusion

Use projection in MongoDB's find() method to retrieve specific field values by their key names. Set field values to 1 for inclusion and 0 for exclusion to control which data is returned.