MongoDB query to return only embedded document?

While MongoDB doesn't return only embedded documents directly, you can use projection to return specific fields and the $elemMatch operator to filter array elements that match certain conditions.

Syntax

db.collection.find(
    { "arrayField.nestedField": { $gte: value } },
    { "arrayField": { $elemMatch: { "nestedField": { $gte: value } } } }
);

Sample Data

db.queryToEmbeddedDocument.insertOne({
    "UserName": "Larry",
    "PostDetails": [
        { "UserMessage": "Hello", "UserLikes": 8 },
        { "UserMessage": "Hi", "UserLikes": 6 },
        { "UserMessage": "Good Morning", "UserLikes": 12 },
        { "UserMessage": "Awesome", "UserLikes": 4 }
    ]
});

Method 1: Using Projection (Returns All Array Elements)

db.queryToEmbeddedDocument.find(
    { "PostDetails.UserLikes": { $gte: 8 } },
    { PostDetails: 1 }
);

{
    "_id": ObjectId("5c988a9f330fd0aa0d2fe4bd"),
    "PostDetails": [
        { "UserMessage": "Hello", "UserLikes": 8 },
        { "UserMessage": "Hi", "UserLikes": 6 },
        { "UserMessage": "Good Morning", "UserLikes": 12 },
        { "UserMessage": "Awesome", "UserLikes": 4 }
    ]
}

Method 2: Using $elemMatch (Returns Only Matching Elements)

db.queryToEmbeddedDocument.find(
    { "PostDetails.UserLikes": { $gte: 8 } },
    { "PostDetails": { $elemMatch: { "UserLikes": { $gte: 8 } } } }
);

{
    "_id": ObjectId("5c988a9f330fd0aa0d2fe4bd"),
    "PostDetails": [
        { "UserMessage": "Hello", "UserLikes": 8 }
    ]
}

Method 3: Using Aggregation Pipeline

db.queryToEmbeddedDocument.aggregate([
    { $match: { "PostDetails.UserLikes": { $gte: 8 } } },
    { $unwind: "$PostDetails" },
    { $match: { "PostDetails.UserLikes": { $gte: 8 } } },
    { $project: { "PostDetails": 1 } }
]);

{ "_id": ObjectId("..."), "PostDetails": { "UserMessage": "Hello", "UserLikes": 8 } }
{ "_id": ObjectId("..."), "PostDetails": { "UserMessage": "Good Morning", "UserLikes": 12 } }

Key Differences

• Projection alone returns the entire array even if only some elements match
• $elemMatch returns only the first matching array element
• Aggregation returns all matching elements as separate documents

Conclusion

Use $elemMatch in projection to return only the first matching embedded document, or use aggregation with $unwind to get all matching elements as separate results.