Fetch specific field values in MongoDB

To fetch specific field values in MongoDB, use the $in operator to match documents where a field value equals any value in a specified array, combined with projection to return only the desired fields.

Syntax

db.collection.find(
    { fieldName: { $in: ["value1", "value2", "value3"] } },
    { field1: 1, field2: 0, _id: 0 }
);

Sample Data

Let us create a collection with student documents ?

db.indexesDemo.insertMany([
    {"StudentFirstName": "John", "StudentLastName": "Smith"},
    {"StudentFirstName": "Chris", "StudentLastName": "Brown"},
    {"StudentFirstName": "John", "StudentLastName": "Doe"},
    {"StudentFirstName": "David", "StudentLastName": "Miller"}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e06de4d25ddae1f53b621dd"),
        ObjectId("5e06de5825ddae1f53b621de"),
        ObjectId("5e06de6725ddae1f53b621df"),
        ObjectId("5e06de7225ddae1f53b621e0")
    ]
}

View All Documents

db.indexesDemo.find();

{ "_id": ObjectId("5e06de4d25ddae1f53b621dd"), "StudentFirstName": "John", "StudentLastName": "Smith" }
{ "_id": ObjectId("5e06de5825ddae1f53b621de"), "StudentFirstName": "Chris", "StudentLastName": "Brown" }
{ "_id": ObjectId("5e06de6725ddae1f53b621df"), "StudentFirstName": "John", "StudentLastName": "Doe" }
{ "_id": ObjectId("5e06de7225ddae1f53b621e0"), "StudentFirstName": "David", "StudentLastName": "Miller" }

Example: Fetch Specific Field Values

Find documents where StudentFirstName is either "John" or "David", returning only the StudentFirstName field ?

db.indexesDemo.find(
    { StudentFirstName: { $in: ["John", "David"] } },
    { _id: 0, StudentLastName: 0 }
);

{ "StudentFirstName": "John" }
{ "StudentFirstName": "John" }
{ "StudentFirstName": "David" }

Key Points

• $in operator matches documents where the field value equals any value in the array.
• Use projection ({ field: 0 }) to exclude unwanted fields from results.
• Set _id: 0 to exclude the default ObjectId field.

Conclusion

The $in operator combined with field projection allows you to efficiently fetch specific field values that match multiple criteria. This approach is useful for filtering and retrieving targeted data from MongoDB collections.