Seed data in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output after running this seed file?

Given this Rails seed file snippet, what will be the count of users in the database after running rails db:seed?

Ruby on Rails

User.create([{ name: 'Alice' }, { name: 'Bob' }])
User.create(name: 'Charlie')
User.create(name: 'Alice')

A 2

B 4

C 3

D 1

💡 Hint

Each create call adds records unless validations prevent it.

The first line creates 2 users, second line adds 1 more, and the third adds another user named 'Alice'. Total is 4 users.

📝 Syntax

intermediate

Which seed syntax will cause a syntax error?

Identify which option will cause a syntax error when running rails db:seed.

A User.create(name: 'Dave', age: 30)

B User.create([{ name: 'Eve' }, { name: 'Frank' }])

C User.create(name: 'Grace' age: 25)

D User.create([{ name: 'Heidi' }])

💡 Hint

Check for missing commas between hash keys.

Option C is missing a comma between name: 'Grace' and age: 25, causing a syntax error.

❓ state_output

advanced

What will be the value of Product.count after seeding?

Consider this seed code snippet. What is the final count of products in the database?

Ruby on Rails

Product.destroy_all
Product.create(name: 'Pen', price: 1.5)
Product.create(name: 'Notebook', price: 3.0)
Product.create(name: 'Pen', price: 1.5)

A 3

B 2

C 0

D 1

💡 Hint

Destroy_all clears all records before creating new ones.

All three create calls add products. No uniqueness validation is shown, so duplicates are allowed. Total is 3.

🔧 Debug

advanced

Why does this seed file fail with a validation error?

This seed file fails when run. What is the most likely cause?

Ruby on Rails

Category.create(name: 'Books')
Category.create(name: 'Books')

A The database connection is not established.

B The <code>Category</code> model does not allow creation without an ID.

C The seed file syntax is invalid due to missing commas.

D The <code>name</code> field must be unique and duplicates cause validation failure.

💡 Hint

Check model validations for uniqueness constraints.

If name is validated as unique in the model, creating two categories with the same name causes a validation error.

🧠 Conceptual

expert

What is the best way to ensure idempotent seed data in Rails?

You want to run rails db:seed multiple times without creating duplicate records. Which approach achieves this?

A Use <code>Model.find_or_create_by</code> with unique attributes to avoid duplicates.

B Use <code>Model.create</code> without checks; duplicates are acceptable.

C Manually delete all records before seeding with <code>Model.destroy_all</code>.

D Run <code>rails db:seed</code> only once and never again.

💡 Hint

Think about how to check if a record exists before creating it.

Using find_or_create_by checks for existing records with given attributes and creates only if none exist, making seeds safe to run multiple times.