Session handling in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Rails controller action regarding session?

Consider this Rails controller action:

def login
  session[:user_id] = 42
  render plain: session[:user_id]
end

What will be the response body when this action is called?

Ruby on Rails

def login
  session[:user_id] = 42
  render plain: session[:user_id]
end

A "nil"

B "42"

C "session[:user_id]"

D "user_id"

💡 Hint

Remember, session stores values as key-value pairs accessible by keys.

The session[:user_id] is set to 42, so rendering session[:user_id] outputs "42" as a string.

❓ state_output

intermediate

What is the session content after this sequence?

Given this sequence in a Rails controller:

session[:cart] = ['apple']
session[:cart] << 'banana'
session[:cart].delete('apple')

What is the value of session[:cart] after these lines?

Ruby on Rails

session[:cart] = ['apple']
session[:cart] << 'banana'
session[:cart].delete('apple')

A ['banana']

B ['apple', 'banana']

C []

D ['apple']

💡 Hint

Think about how arrays change with << and delete methods.

Initially cart has ['apple'], then 'banana' is added, then 'apple' is removed, leaving ['banana'].

📝 Syntax

advanced

Which option correctly sets a flash message in Rails session?

Which of these lines correctly sets a flash notice message in a Rails controller?

A session[:flash] = "Welcome!"

B session.flash[:notice] = "Welcome!"

C flash.notice = "Welcome!"

D flash[:notice] = "Welcome!"

💡 Hint

Flash messages use a special hash called flash.

flash is a hash-like object; setting flash[:notice] = "Welcome!" is correct syntax.

🔧 Debug

advanced

Why does this session assignment not persist across requests?

In a Rails controller, this code is used:

def set_user
  user = User.find(params[:id])
  session[:user] = user
  render plain: "User set"
end

Why might session[:user] not persist correctly across requests?

Ruby on Rails

def set_user
  user = User.find(params[:id])
  session[:user] = user
  render plain: "User set"
end

A Because User.find returns nil if user not found, causing session to clear

B Because session[:user] key is reserved and cannot be used

C Because session can only store simple data types, not ActiveRecord objects

D Because render plain disables session storage

💡 Hint

Think about what kind of data can be stored in session.

Sessions store simple data like strings or numbers. Storing complex objects like ActiveRecord instances causes issues.

🧠 Conceptual

expert

What is the main security risk of storing sensitive data in Rails session?

Why is it risky to store sensitive information like passwords or credit card numbers directly in Rails session?

A Because session data is stored client-side and can be tampered with if not encrypted

B Because sessions automatically expire after 5 minutes, losing data

C Because Rails encrypts session data making it impossible to read later

D Because storing data in session causes server crashes under load

💡 Hint

Consider where session data is stored and how it can be accessed.

Rails stores session data in cookies by default, which are client-side and can be read or modified if not properly secured.

Practice

1. What is the main purpose of using session in a Rails application?

easy

A. To style the webpage dynamically

B. To handle file uploads

C. To connect to the database

D. To store user data across multiple requests

Solution

1. Step 1: Understand what sessions do

   Sessions keep data between different pages or requests for the same user.

2. Step 2: Identify the correct purpose

   Storing user data like login status or preferences is the main use of sessions.

3. Final Answer:

   To store user data across multiple requests -> Option D

4. Quick Check:

   Sessions remember user info across pages = B [OK]

Hint: Sessions keep user info between pages [OK]

Common Mistakes:

• Confusing sessions with styling or database connections
• Thinking sessions handle file uploads

2. Which of the following is the correct way to store a user's name in the session in Rails?

easy

A. session = { name: 'Alice' }

B. session[:name] = 'Alice'

C. session.name = 'Alice'

D. session('name') = 'Alice'

Solution

1. Step 1: Recall session syntax in Rails

   Sessions use a hash-like syntax with square brackets and symbols for keys.

2. Step 2: Match the correct syntax

   Assigning with session[:name] = 'Alice' is the proper way.

3. Final Answer:

   session[:name] = 'Alice' -> Option B

4. Quick Check:

   Use session[:key] = value syntax = A [OK]

Hint: Use session[:key] = value to store data [OK]

Common Mistakes:

• Using assignment with equals on session itself
• Trying to call session like a method
• Using dot notation which is invalid

3. What will be the output of the following Rails controller code snippet?

session[:count] ||= 0
session[:count] += 1
render plain: session[:count]

medium

A. nil

B. 0

C. 1

D. Error

Solution

1. Step 1: Understand the ||= operator

   If session[:count] is nil or false, it sets it to 0; otherwise, it keeps the value.

2. Step 2: Increment the count

   After setting to 0 if needed, it adds 1, so the value becomes 1.

3. Final Answer:

   1 -> Option C

4. Quick Check:

   Initialize or keep count, then add 1 = 1 [OK]

Hint: ||= sets default, then += increments [OK]

Common Mistakes:

• Thinking ||= 0 sets count to 0 every time
• Expecting output 0 instead of 1
• Assuming session[:count] is nil after increment

4. Identify the error in this Rails controller code that tries to clear the session:

def logout
  session.clear()
  redirect_to root_path
end

medium

A. No error; code correctly clears the session

B. Missing parentheses in session.clear call

C. session.clear should be session.delete_all

D. session.clear is not a valid method

Solution

1. Step 1: Check session clearing methods in Rails

   Rails session supports clear method to remove all keys.

2. Step 2: Verify syntax and usage

   Calling session.clear() is valid and clears the session.

3. Final Answer:

   No error; code correctly clears the session -> Option A

4. Quick Check:

   session.clear() clears session correctly = D [OK]

Hint: session.clear() empties session data correctly [OK]

Common Mistakes:

• Thinking session.clear() is invalid
• Confusing with database delete methods
• Assuming parentheses are mandatory or cause error

5. You want to store a user's preferred language in the session only if it is not already set. Which code snippet correctly does this in a Rails controller?

hard

A. All of the above

B. session[:language] ||= params[:language]

C. session[:language] = params[:language] if session[:language].nil?

D. session[:language] = params[:language] unless session[:language]

Solution

1. Step 1: Understand the goal

   We want to set session[:language] only if it is not already set.

2. Step 2: Analyze each option

   session[:language] = params[:language] if session[:language].nil? uses if session[:language].nil?, which sets only if nil.
   session[:language] ||= params[:language] uses ||= which sets if false or nil.
   session[:language] = params[:language] unless session[:language] uses unless session[:language], which sets if false or nil.
   All three effectively do the same thing.

3. Final Answer:

   All of the above -> Option A

4. Quick Check:

   All three set only if session[:language] is unset = C [OK]

Hint: ||= or conditional assignment both work [OK]

Common Mistakes:

• Thinking only ||= works
• Confusing unless with if
• Setting session unconditionally