Joins vs embedding decision in MongoDB - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to embed an address inside a user document in MongoDB.

MongoDB

db.users.insertOne({ name: "Alice", address: [1] })

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AObjectId("507f1f77bcf86cd799439011")

B[ "123 Main St", "Townsville" ]

C{ street: "123 Main St", city: "Townsville" }

D"123 Main St, Townsville"

Attempts:

3 left

💡 Hint

Common Mistakes

Using an array instead of an object for the address.

Using a string instead of a structured object.

Referencing an ObjectId instead of embedding the data.

Embedding an address as a sub-document uses an object with fields like street and city.

2fill in blank

medium

Complete the code to perform a $lookup join between orders and customers collections.

MongoDB

db.orders.aggregate([{ $lookup: { from: "[1]", localField: "customerId", foreignField: "_id", as: "customerInfo" } }])

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Aproducts

Baddresses

Corders

Dcustomers

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong collection name in the 'from' field.

Joining with the same collection instead of the related one.

The $lookup stage joins the orders collection with the customers collection using matching fields.

3fill in blank

hard

Fix the error in the query to embed multiple phone numbers inside a user document.

MongoDB

db.users.insertOne({ name: "Bob", phones: [1] })

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A[ { type: "home", number: "123-4567" }, { type: "work", number: "987-6543" } ]

B{ home: "123-4567", work: "987-6543" }

C"123-4567, 987-6543"

DObjectId("507f1f77bcf86cd799439012")

Attempts:

3 left

💡 Hint

Common Mistakes

Using a single object instead of an array for multiple phones.

Using a string or ObjectId instead of structured data.

Embedding multiple phone numbers requires an array of objects, each with type and number fields.

4fill in blank

hard

Fill both blanks to write a $lookup that joins orders with products and filters only orders with quantity greater than 5.

MongoDB

db.orders.aggregate([{ $lookup: { from: "[1]", localField: "productId", foreignField: "_id", as: "productDetails" } }, { $match: { quantity: { [2]: 5 } } }])

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Aproducts

B$gt

C$lt

Dcustomers

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong collection name in $lookup.

Using $lt instead of $gt for filtering.

The $lookup joins with the products collection. The $match filters orders where quantity is greater than 5 using $gt.

5fill in blank

hard

Fill all three blanks to create a query that embeds a review inside a product document only if the rating is 4 or higher.

MongoDB

db.products.updateOne({ _id: [1] }, { $push: { reviews: { userId: [2], rating: [3] } } })

Drag options to blanks, or click blank then click option'

AObjectId("507f1f77bcf86cd799439013")

BObjectId("507f1f77bcf86cd799439014")

C4

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using string literals instead of ObjectId for IDs.

Using a rating less than 4.

The product _id and userId are ObjectIds. The rating must be 4 or higher, so 4 is used here.