Form object pattern in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a form object class inheriting from ActiveModel::Model.

Ruby on Rails

class UserForm
  include [1]

  attr_accessor :name, :email
end

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

AActiveModel::Model

BActiveRecord::Base

CActionController::Base

DActiveSupport::Concern

Attempts:

3 left

💡 Hint

Common Mistakes

Using ActiveRecord::Base instead of ActiveModel::Model

Forgetting to include any module

The form object pattern uses ActiveModel::Model to get model-like behavior without database persistence.

2fill in blank

medium

Complete the code to add a validation for presence of :email in the form object.

Ruby on Rails

class UserForm
  include ActiveModel::Model

  attr_accessor :name, :email

  validates :email, [1]: true
end

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

Auniqueness

Bformat

Cpresence

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'length' instead of 'presence' for required fields

Using 'uniqueness' which requires database

Use validates :email, presence: true to ensure the email is not blank.

3fill in blank

hard

Fix the error in the save method to return false if the form is invalid.

Ruby on Rails

def save
  return false unless [1]
  # persist data here
  true
end

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

Avalidate

Bsave!

Cvalidates

Dvalid?

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'validate' which runs validations but does not return boolean

Using 'save!' which is for ActiveRecord models

The valid? method runs validations and returns true or false.

4fill in blank

hard

Fill both blanks to define an initialize method that sets attributes from params hash.

Ruby on Rails

def initialize(params = {})
  params.each do |key, value|
    [1].send("[2]=", value)
  end
end

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

Aself

Bparams

Ckey

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'params.send' instead of 'self.send'

Using 'value' instead of 'key' for method name

Use self.send("key=", value) to assign each attribute dynamically.

5fill in blank

hard

Fill all three blanks to define a save method that validates, creates a User, and returns true if successful.

Ruby on Rails

def save
  return false unless [1]
  user = User.new(name: [2], email: [3])
  user.save
end

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

Avalid?

Bname

Cemail

Dsave!

Attempts:

3 left

💡 Hint

Common Mistakes

Calling save! instead of save which raises exceptions

Not checking validity before saving

The save method first checks validity, then creates a User with form attributes, and saves it.

Practice

1. What is the main purpose of using a Form Object in Rails?

easy

A. To speed up database queries

B. To replace ActiveRecord models completely

C. To separate form validation and logic from database models

D. To generate HTML forms automatically

Solution

1. Step 1: Understand the role of form objects

   Form objects are used to keep form-related logic and validations separate from the database models.

2. Step 2: Compare with other options

   They do not replace ActiveRecord models or speed up queries, nor do they generate HTML forms automatically.

3. Final Answer:

   To separate form validation and logic from database models -> Option C

4. Quick Check:

   Form object purpose = Separation of form logic [OK]

Hint: Form objects separate form logic from models [OK]

Common Mistakes:

• Thinking form objects replace database models
• Assuming form objects speed up queries
• Confusing form objects with view helpers

2. Which module is commonly included in a Rails form object to provide model-like behavior?

easy

A. ActiveModel::Model

B. ActiveRecord::Base

C. ActionController::Base

D. ActiveSupport::Concern

Solution

1. Step 1: Identify the module for model-like behavior without DB

   The ActiveModel::Model module allows plain Ruby objects to behave like ActiveRecord models, including validations.

2. Step 2: Eliminate other options

   ActiveRecord::Base is for database models, ActionController::Base is for controllers, and ActiveSupport::Concern is for mixins.

3. Final Answer:

   ActiveModel::Model -> Option A

4. Quick Check:

   Form object module = ActiveModel::Model [OK]

Hint: Form objects include ActiveModel::Model for validations [OK]

Common Mistakes:

• Using ActiveRecord::Base in form objects
• Confusing controller modules with model modules
• Forgetting to include any module

3. Given this form object code, what will user_form.valid? return if email is blank?

class UserForm
  include ActiveModel::Model
  attr_accessor :email
  validates :email, presence: true
end

user_form = UserForm.new(email: '')
user_form.valid?

medium

A. true

B. false

C. nil

D. Raises an error

Solution

1. Step 1: Check validation rules

   The form object requires email to be present (not blank).

2. Step 2: Evaluate given input

   The email is an empty string, which fails the presence validation, so valid? returns false.

3. Final Answer:

   false -> Option B

4. Quick Check:

   Blank email fails presence validation = false [OK]

Hint: Presence validation fails on blank string [OK]

Common Mistakes:

• Assuming blank string passes presence validation
• Expecting valid? to raise error on blank
• Confusing nil and empty string behavior

4. Identify the error in this form object code:

class OrderForm
  include ActiveModel::Model
  attr_accessor :quantity
  validates :quantity, numericality: { greater_than: 0 }

  def save
    if valid?
      Order.create(quantity: quantity)
    end
  end
end

medium

A. Missing return value in save method

B. Order model is not defined

C. quantity is a string, needs conversion before validation

D. No error, code is correct

Solution

1. Step 1: Verify syntax and structure

   The code properly includes ActiveModel::Model, defines attr_accessor, and sets up numericality validation. Syntax is valid.

2. Step 2: Confirm behavior

   Numericality validation internally handles string-to-number conversion (e.g., '5' validates as > 0). The save method returns the Order instance (truthy) on success or nil/falsey otherwise, which works in conditionals.

3. Final Answer:

   No error, code is correct -> Option D

4. Quick Check:

   Numericality handles strings; save pattern acceptable [OK]

Hint: Rails numericality validator handles numeric strings automatically [OK]

Common Mistakes:

• Thinking strings need manual conversion for numericality
• Overthinking save method's return value
• Assuming undefined models cause errors in examples

5. You want to create a form object that handles user registration with email, password, and password_confirmation. Which approach correctly ensures password confirmation validation and saves the user if valid?

class RegistrationForm
  include ActiveModel::Model
  attr_accessor :email, :password, :password_confirmation

  validates :email, presence: true
  validates :password, presence: true, confirmation: true

  def save
    if valid?
      User.create(email: email, password: password)
    end
  end
end

hard

A. This code correctly validates and saves the user with password confirmation

B. Missing manual check for password_confirmation equality

C. Should use validates_confirmation_of :password_confirmation instead

D. Must call super in save method to save user

Solution

1. Step 1: Check validations for password confirmation

   The confirmation: true option on password automatically validates that password_confirmation matches.

2. Step 2: Verify save method logic

   The save method calls valid? and creates the user if valid, which is the correct pattern.

3. Final Answer:

   This code correctly validates and saves the user with password confirmation -> Option A

4. Quick Check:

   Password confirmation validation works with confirmation: true [OK]

Hint: Use confirmation: true for password confirmation validation [OK]

Common Mistakes:

• Manually checking password_confirmation equality
• Using deprecated validates_confirmation_of syntax
• Forgetting to call valid? before save