How to select a single field in MongoDB?

You can select a single field in MongoDB using the projection parameter in the find() method. Projection lets you specify which fields to include or exclude in the query results. The syntax is −

db.yourCollectionName.find(
    {"yourFieldName": yourValue},
    {"yourSingleFieldName": 1, _id: 0}
);

In the above syntax, "yourSingleFieldName": 1 means include this field in the result, and _id: 0 means exclude the _id field which MongoDB includes by default.

Creating a Sample Collection

To understand the above syntax, let us create a collection with documents ?

db.singleFieldDemo.insertOne({"StudentName": "David", "StudentAge": 28});
db.singleFieldDemo.insertOne({"StudentName": "Bob", "StudentAge": 18});
db.singleFieldDemo.insertOne({"StudentName": "Chris", "StudentAge": 24});
db.singleFieldDemo.insertOne({"StudentName": "Robert", "StudentAge": 26});

Now display all documents from the collection using the find() method −

db.singleFieldDemo.find().pretty();

The following is the output −

{
    "_id" : ObjectId("5c6eba356fd07954a489067c"),
    "StudentName" : "David",
    "StudentAge" : 28
}
{
    "_id" : ObjectId("5c6eba406fd07954a489067d"),
    "StudentName" : "Bob",
    "StudentAge" : 18
}
{
    "_id" : ObjectId("5c6eba4c6fd07954a489067e"),
    "StudentName" : "Chris",
    "StudentAge" : 24
}
{
    "_id" : ObjectId("5c6eba586fd07954a489067f"),
    "StudentName" : "Robert",
    "StudentAge" : 26
}

Selecting a Single Field

Here is the query to select only the StudentName field for the student whose age is 18 −

db.singleFieldDemo.find(
    {"StudentAge": 18},
    {"StudentName": 1, "_id": 0}
);

The following is the output −

{ "StudentName" : "Bob" }

Only the StudentName field is returned. The _id field is excluded because we set _id: 0, and StudentAge is excluded because we did not set it to 1 in the projection.

Selecting a Single Field for All Documents

To retrieve a single field from all documents (without filtering), pass an empty query object as the first parameter ?

db.singleFieldDemo.find(
    {},
    {"StudentName": 1, "_id": 0}
);

The following is the output −

{ "StudentName" : "David" }
{ "StudentName" : "Bob" }
{ "StudentName" : "Chris" }
{ "StudentName" : "Robert" }

Conclusion

Use the projection parameter in MongoDB's find() method to select a single field. Set the desired field to 1 to include it and _id to 0 to exclude the default ID field from the results.