CRUD operations through models in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Rails model code output after creation?

Consider the following Rails model code snippet. What will be the value of user.name after running this code?

Ruby on Rails

user = User.create(name: "Alice", age: 30)
user.name

A "Alice"

B nil

C ""

D Raises ActiveRecord::RecordInvalid error

💡 Hint

The create method saves the record and returns the object with attributes set.

The create method in Rails creates and saves a new record. The returned object has the attributes assigned, so user.name will be "Alice".

❓ state_output

intermediate

What is the value of user.persisted? after new and save?

Given the following code, what will user.persisted? return after the save call?

Ruby on Rails

user = User.new(name: "Bob")
saved = user.save
user.persisted?

A false

B true

C nil

D Raises NoMethodError

💡 Hint

The save method returns true if the record was saved successfully.

After calling save on a new record, if it succeeds, the record is persisted in the database. Thus, user.persisted? returns true.

🔧 Debug

advanced

Why does this update raise an error?

Examine the code below. Why does user.update(name: nil) raise an error if the model validates presence of name?

Ruby on Rails

user = User.find(1)
user.update(name: nil)

A Validation fails because name cannot be nil, so update returns false and does not raise error

B update raises ActiveRecord::RecordInvalid because validations fail and update! was called

C update raises NoMethodError because name is nil

D update raises ActiveRecord::RecordNotFound because user id 1 does not exist

💡 Hint

Check if update or update! is used and how validations behave.

The update method returns false if validations fail but does not raise an error. Only update! raises an exception on validation failure.

📝 Syntax

advanced

Which option correctly deletes a record by id?

Which of the following Rails model commands correctly deletes the user with id 5 from the database?

A User.delete(5)

B User.remove(5)

C User.destroy(5)

D User.destroy_by(id: 5)

💡 Hint

Consider which methods trigger callbacks and which do not.

destroy deletes the record and runs callbacks. delete deletes without callbacks. remove is not a valid method. destroy_by deletes by conditions but returns the number of records deleted.

🧠 Conceptual

expert

What is the result of chaining update and reload?

Given this code, what will user.name be after the last line?

Ruby on Rails

user = User.create(name: "Carol")
user.update(name: "Diana")
user.reload
user.name

A nil

B "Carol"

C Raises ActiveRecord::RecordNotFound

D "Diana"

💡 Hint

The reload method refreshes the object from the database.

The update changes the name to "Diana" in the database. reload refreshes the object with the latest data, so user.name is "Diana".