Custom validation methods in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a custom validation method in a Rails model.

Ruby on Rails

class User < ApplicationRecord
  validate :[1]

  def custom_age_check
    errors.add(:age, "must be at least 18") if age < 18
  end
end

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

Acheck_age

Bvalidate_age

Ccustom_age_check

Dage_check

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name in the validate call than the method defined.

Forgetting to define the custom validation method.

The method name used in the validate call must match the custom validation method defined in the model.

2fill in blank

medium

Complete the code to add an error message inside the custom validation method.

Ruby on Rails

def check_username
  if username.blank?
    errors.[1](:username, "can't be blank")
  end
end

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

Aappend

Badd_error

Cpush

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'add_error' or other incorrect method names.

Forgetting to specify the attribute when adding errors.

The correct method to add an error message in Rails validations is 'errors.add'.

3fill in blank

hard

Fix the error in the custom validation method to correctly check if email contains '@'.

Ruby on Rails

def email_format
  unless email.[1]('@')
    errors.add(:email, "must contain @")
  end
end

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

Ainclude?

Bcontains

Chas

Dincludes

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like 'contains' or 'has'.

Forgetting the question mark at the end of 'include?'.

The correct Ruby method to check if a string contains a substring is 'include?'.

4fill in blank

hard

Fill both blanks to create a custom validation that checks if password length is at least 6.

Ruby on Rails

def password_length_check
  if password.[1] < [2]
    errors.add(:password, "is too short")
  end
end

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

Alength

B6

Csize

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'size' instead of 'length' (both work but only one is correct here).

Using the wrong number for minimum length.

Use 'length' to get the password length and compare it to 6 for minimum length validation.

5fill in blank

hard

Fill all three blanks to create a custom validation that adds an error if age is not between 18 and 65.

Ruby on Rails

def age_range_check
  unless age [1] 18 [2] age [3] 65
    errors.add(:age, "must be between 18 and 65")
  end
end

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

A>=

B<=

C&&

D||

Attempts:

3 left

💡 Hint

Common Mistakes

Using '||' instead of '&&' which allows invalid ages.

Reversing the comparison operators.

Check that age is greater or equal to 18 and less or equal to 65 using '>=' and '<=' with '&&' between conditions.

Practice

1. What is the main purpose of a custom validation method in a Rails model?

easy

A. To add your own rules for checking data before saving

B. To automatically generate database tables

C. To create user interface elements

D. To speed up database queries

Solution

1. Step 1: Understand validation role in Rails

   Validations check data correctness before saving to the database.

2. Step 2: Identify custom validation purpose

   Custom validations let you write your own rules beyond built-in checks.

3. Final Answer:

   To add your own rules for checking data before saving -> Option A

4. Quick Check:

   Custom validation = custom data rules [OK]

Hint: Custom validations add your own data rules [OK]

Common Mistakes:

• Confusing validations with database setup
• Thinking validations create UI elements
• Assuming validations improve query speed

2. Which is the correct way to add a custom validation method named check_age in a Rails model?

easy

A. validates :check_age

B. validate :check_age

C. validate_check_age

D. validates_with :check_age

Solution

1. Step 1: Recall syntax for custom validations

   Use validate :method_name to call a custom method.

2. Step 2: Match method name with syntax

   For method check_age, syntax is validate :check_age.

3. Final Answer:

   validate :check_age -> Option B

4. Quick Check:

   Custom validation syntax = validate :method_name [OK]

Hint: Use 'validate :method_name' for custom validations [OK]

Common Mistakes:

• Using 'validates' instead of 'validate' for custom methods
• Adding underscores in method call
• Using 'validates_with' incorrectly

3. Given this model code:

class User < ApplicationRecord
  validate :check_name

  def check_name
    errors.add(:name, "can't be blank") if name.blank?
  end
end

What happens if you try to save a User with name = ''?

medium

A. The save fails with an error on the name attribute

B. The save succeeds without errors

C. A syntax error occurs

D. The save fails but no error message is added

Solution

1. Step 1: Understand the custom validation logic

   The method adds an error if name.blank? is true (empty string).

2. Step 2: Effect on saving a User with empty name

   Since name is blank, error is added and save fails.

3. Final Answer:

   The save fails with an error on the name attribute -> Option A

4. Quick Check:

   Blank name triggers error = save fails [OK]

Hint: Blank fields trigger errors in custom validations [OK]

Common Mistakes:

• Assuming save succeeds despite errors
• Confusing blank? with nil check
• Expecting syntax errors from valid code

4. Identify the error in this custom validation method:

class Product < ApplicationRecord
  validate :check_price

  def check_price
    errors.add(:price, "must be positive") if price <= 0
  end
end

medium

A. The method name should start with 'validate_'

B. The validation should use 'validates' instead of 'validate'

C. No error; the code is correct

D. The comparison operator should be '==' instead of '<='

Solution

1. Step 1: Check method naming and usage

   Custom validation methods do not need 'validate_' prefix; 'validate :method' is correct.

2. Step 2: Verify validation logic and syntax

   Using 'validate' with method and condition 'price <= 0' is valid Ruby and Rails syntax.

3. Final Answer:

   No error; the code is correct -> Option C

4. Quick Check:

   Custom validation syntax and logic are correct [OK]

Hint: Custom validation methods do not need special prefixes [OK]

Common Mistakes:

• Adding 'validate_' prefix to method name
• Using 'validates' for custom methods
• Changing correct comparison operators

5. You want to create a custom validation that ensures a User's username is at least 5 characters and contains no spaces. Which code correctly implements this?

hard

A. validate :username_rules

def username_rules
errors.add(:username, "invalid") if username.length <= 5 && username.include?(" ")
end

B. validates :username, length: { minimum: 5 }, format: { without: /\s/ }

C. validate :username_rules

def username_rules
errors.add(:username, "invalid") unless username.length >= 5 && !username.include:(" ")
end

D. validate :username_rules

def username_rules
if username.length < 5 || username.include?(" ")
errors.add(:username, "must be 5+ chars and no spaces")
end
end

Solution

1. Step 1: Understand the validation requirements

   Username must be at least 5 characters and contain no spaces.

2. Step 2: Analyze each option's logic

   validate :username_rules
   
   def username_rules
     if username.length < 5 || username.include?(" ")
       errors.add(:username, "must be 5+ chars and no spaces")
     end
   end

   uses OR logic to add error if username is shorter than 5 or contains spaces, which matches requirements.

3. Step 3: Check other options

   validates :username, length: { minimum: 5 }, format: { without: /\s/ }

   uses built-in validations, not custom method.

   validate :username_rules
   
   def username_rules
     errors.add(:username, "invalid") unless username.length >= 5 && !username.include:(" ")
   end

   has syntax error with colon in method call.

   validate :username_rules
   
   def username_rules
     errors.add(:username, "invalid") if username.length <= 5 && username.include?(" ")
   end

   uses wrong comparison (<= 5 excludes 5).

4. Final Answer:

   validate :username_rules def username_rules if username.length < 5 || username.include?(" ") errors.add(:username, "must be 5+ chars and no spaces") end end -> Option D

5. Quick Check:

   Custom validation logic matches requirements [OK]

Hint: Check logic carefully: use OR for combined invalid conditions [OK]

Common Mistakes:

• Using AND instead of OR for combined conditions
• Confusing built-in validations with custom methods
• Wrong comparison operators causing off-by-one errors