Many-to-many with references in MongoDB - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find all books that a specific author wrote by matching the author's ID.

MongoDB

db.books.find({ authors: [1] })

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

A"authorId789"

B"authorId456"

C"authorId123"

D"authorId000"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong author ID string.

Not putting the author ID in quotes.

Trying to match the entire authors array instead of an element.

The query filters books where the authors array contains the specific author ID. Replace {{BLANK_1}} with the correct author ID string.

2fill in blank

medium

Complete the code to add a new author ID to a book's authors array using the $push operator.

MongoDB

db.books.updateOne({ _id: bookId }, { $push: { authors: [1] } })

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

AnewAuthorId

B"newAuthorId"

C{ newAuthorId }

D["newAuthorId"]

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the author ID.

Using an array or object instead of a string.

Using the wrong update operator.

The $push operator adds a single element to the array. The author ID must be a string, so it needs quotes.

3fill in blank

hard

Fix the error in the aggregation pipeline stage to lookup authors for each book.

MongoDB

{ $lookup: { from: "authors", localField: "authors", foreignField: [1], as: "authorDetails" } }

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

A"_id"

B"id"

C"authorId"

D"authors"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong field name for foreignField.

Confusing localField and foreignField.

Using a field that does not exist in the authors collection.

The foreignField should be the field in the authors collection that matches the IDs stored in the books' authors array. Usually, this is _id.

4fill in blank

hard

Fill both blanks to create a query that finds authors who wrote a book with a specific title.

MongoDB

db.authors.find({ _id: { $in: db.books.findOne({ title: [1] }).[2] }) })

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

A"The Great Adventure"

Bauthors

CauthorIds

Dwriters

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong field name for author IDs in the book document.

Not quoting the book title string.

Using a field name that does not exist.

The query finds the book by title, then uses the authors array field to find matching author IDs.

5fill in blank

hard

Fill all three blanks to create an aggregation pipeline that joins books with authors and filters books published after 2010.

MongoDB

[ { $match: { year: { $[1]: [2] } } }, { $lookup: { from: "authors", localField: "authors", foreignField: [3], as: "authorInfo" } } ]

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

Agt

B2010

C"_id"

Dgte

Attempts:

3 left

💡 Hint

Common Mistakes

Using $gte instead of $gt when strictly greater is needed.

Not quoting the year number correctly.

Using wrong field names in $lookup.

The $match stage filters books where the year is greater than 2010 using $gt. The $lookup joins authors by matching the _id field.