Field selection within MongoDB query using dot notation?

Field selection in MongoDB using dot notation allows you to access and filter nested fields within embedded documents or arrays. Use dot notation to specify which fields to include or exclude in query results.

Syntax

db.collection.find(
    {"parentField.nestedField": "value"},
    {"parentField.specificField": 1/0}
);

Sample Data

db.demo302.insertMany([
    {"Id": 101, "details": [{"Name": "Chris", "Age": 21, "Subject": "MySQL"}]},
    {"Id": 102, "details": [{"Name": "Bob", "Age": 23, "Subject": "MongoDB"}]},
    {"Id": 103, "details": [{"Name": "David", "Age": 20, "Subject": "Java"}]}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e4d746f5d93261e4bc9ea52"),
        ObjectId("5e4d74815d93261e4bc9ea53"),
        ObjectId("5e4d74955d93261e4bc9ea54")
    ]
}

Display All Documents

db.demo302.find();

{ "_id" : ObjectId("5e4d746f5d93261e4bc9ea52"), "Id" : 101, "details" : [ { "Name" : "Chris", "Age" : 21, "Subject" : "MySQL" } ] }
{ "_id" : ObjectId("5e4d74815d93261e4bc9ea53"), "Id" : 102, "details" : [ { "Name" : "Bob", "Age" : 23, "Subject" : "MongoDB" } ] }
{ "_id" : ObjectId("5e4d74955d93261e4bc9ea54"), "Id" : 103, "details" : [ { "Name" : "David", "Age" : 20, "Subject" : "Java" } ] }

Example: Field Selection Using Dot Notation

Query documents where Subject is "MongoDB" and exclude Name, Age, _id, and Id fields ?

db.demo302.find(
    {"details.Subject": "MongoDB"},
    {"details.Name": 0, "details.Age": 0, "_id": 0, "Id": 0}
);

{ "details" : [ { "Subject" : "MongoDB" } ] }

Key Points

• Use parentField.nestedField syntax to access nested fields in arrays or embedded documents.
• Field projection: 1 includes the field, 0 excludes it.
• Dot notation works for both query conditions and field selection.

Conclusion

Dot notation enables precise field selection within nested MongoDB documents. Combine it with projection operators to control which nested fields appear in query results, making data retrieval more efficient and focused.