Database query optimization in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to fetch all users with a single query.

Ruby on Rails

users = User.[1]

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

Afind

Bwhere

Call

Dpluck

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'find' without an ID causes an error.

Using 'pluck' returns only specific columns, not full records.

The all method fetches all records in one query.

2fill in blank

medium

Complete the code to eager load associated posts with users.

Ruby on Rails

users = User.[1](:posts)

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

Agroup

Bjoins

Cselect

Dincludes

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'joins' does not eager load and can cause N+1 queries.

Using 'select' changes columns returned but does not eager load.

The includes method eager loads associations to reduce queries.

3fill in blank

hard

Fix the error in the query to find users older than 30.

Ruby on Rails

users = User.where("age [1] ?", 30)

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

A>

B!=

C<

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' returns only users exactly 30 years old.

Using '<' returns users younger than 30.

The operator > correctly filters users older than 30.

4fill in blank

hard

Fill both blanks to optimize fetching user emails for active users.

Ruby on Rails

emails = User.where(active: [1]).[2](:email)

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

Atrue

Bfalse

Cpluck

Dselect

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'false' fetches inactive users.

Using 'select' returns ActiveRecord objects, not just emails.

Filtering active users with true and using pluck fetches only emails efficiently.

5fill in blank

hard

Fill all three blanks to create a hash of user names and their post counts for users with more than 5 posts.

Ruby on Rails

result = User.joins(:posts).group([1]).having("COUNT(posts.id) [2] ?", [3]).count

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

A:name

B>

C5

D:email

Attempts:

3 left

💡 Hint

Common Mistakes

Grouping by :email changes the hash keys incorrectly.

Using '<' or '=' filters wrong post counts.

Grouping by :name, filtering with > 5 posts, and counting returns the desired hash.