Query for values (not objects) in list with MongoDB

To query for values in list, use the positional operator ($) in MongoDB. The $ operator projects only the first matching array element that satisfies the query condition.

Syntax

db.collection.find(
    { "arrayField": "value" },
    { "arrayField.$": 1 }
);

Sample Data

Let us create a collection with documents ?

db.demo628.insertMany([
    { id: 1, Name: ["Chris", "David", "John"] },
    { id: 1, Name: ["Carol", "Sam"] },
    { id: 2, Name: ["Mike", "Sam", "John"] }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e9ae7ea6c954c74be91e6b6"),
        ObjectId("5e9ae7f26c954c74be91e6b7"),
        ObjectId("5e9ae8056c954c74be91e6b8")
    ]
}

Display all documents from a collection with the help of find() method ?

db.demo628.find();

{ "_id": ObjectId("5e9ae7ea6c954c74be91e6b6"), "id": 1, "Name": ["Chris", "David", "John"] }
{ "_id": ObjectId("5e9ae7f26c954c74be91e6b7"), "id": 1, "Name": ["Carol", "Sam"] }
{ "_id": ObjectId("5e9ae8056c954c74be91e6b8"), "id": 2, "Name": ["Mike", "Sam", "John"] }

Example: Query for Values in List

Query for values (not objects) in list ?

db.demo628.find(
    { "Name": "John" },
    { "id": 1, "Name.$": 1 }
);

{ "_id": ObjectId("5e9ae7ea6c954c74be91e6b6"), "id": 1, "Name": ["John"] }
{ "_id": ObjectId("5e9ae8056c954c74be91e6b8"), "id": 2, "Name": ["John"] }

Key Points

• The $ operator returns only the first matching element from the array
• Use "arrayField.$": 1 in the projection to get the matched value
• The query condition must match at least one array element for the document to be returned

Conclusion

The positional operator $ allows you to project specific array values that match your query condition. This is useful when you need to retrieve only the matching array elements instead of the entire array.