One-to-many embedding pattern in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to embed multiple comments inside a blog post document.

MongoDB

db.posts.insertOne({ title: "My Post", comments: [[1]] })

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

A{ text: "Great post!" }

B[{ text: "Great post!" }, { text: "Thanks for sharing." }]

C"Great post!", "Thanks for sharing."

D{ text: "Great post!" }, { text: "Thanks for sharing." }

Attempts:

3 left

💡 Hint

Common Mistakes

Putting comments as strings instead of objects.

Wrapping the array of comments in extra brackets.

The comments field is an array of embedded documents. Each comment is an object inside the array.

2fill in blank

medium

Complete the query to find posts that have at least one comment with text 'Nice!'.

MongoDB

db.posts.find({ comments: { $elemMatch: { text: [1] } } })

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

ANice!

B"Nice!"

C{ $eq: "Nice!" }

D/Nice!/

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the string.

Using a regex instead of exact match.

The $elemMatch operator matches array elements. The text field must equal the string "Nice!".

3fill in blank

hard

Fix the error in the update to add a new comment to the post with _id 1.

MongoDB

db.posts.updateOne({ _id: 1 }, { [1]: { comments: { text: "New comment" } } })

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

A$push

B$add

C$set

D$insert

Attempts:

3 left

💡 Hint

Common Mistakes

Using $set which replaces the whole array instead of adding.

Using non-existent operators like $add or $insert.

The $push operator adds an element to an array field. Here, it adds a new comment object to the comments array.

4fill in blank

hard

Fill both blanks to update the text of the first comment in the post with _id 2.

MongoDB

db.posts.updateOne({ _id: 2 }, { [1]: { "comments.[2].text": "Updated comment" } })

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

A$set

B$push

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using $push which adds a new comment instead of updating.

Using index 1 which targets the second comment.

Use $set to update a specific field. The first comment is at index 0 in the comments array.

5fill in blank

hard

Fill the blanks to remove comments with text 'Spam' from the post with _id 3.

MongoDB

db.posts.updateOne({ _id: 3 }, { [1]: { comments: { text: [2] } } })

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

A$pull

B$pop

C"Spam"

D"spam"

Attempts:

3 left

💡 Hint

Common Mistakes

Using $pop which removes only the first or last element.

Using wrong case in the string value.

The $pull operator removes all array elements that match a condition. Here, it removes comments where text equals "Spam".