Presence validation in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a presence validation for the :name attribute in a Rails model.

Ruby on Rails

validates :name, [1]: true

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

Anumericality

Blength

Cpresence

Duniqueness

Attempts:

3 left

💡 Hint

Common Mistakes

Using length instead of presence

Using uniqueness which checks for duplicates, not presence

The presence validation ensures that the attribute is not empty or nil.

2fill in blank

medium

Complete the code to validate presence of :email with a custom error message.

Ruby on Rails

validates :email, presence: [1]

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

Afalse

Btrue

Cnil

Doptional

Attempts:

3 left

💡 Hint

Common Mistakes

Using false disables validation

Using nil or optional are not valid options here

Setting presence: true activates the presence validation.

3fill in blank

hard

Fix the error in the validation code to correctly validate presence of :title.

Ruby on Rails

validates :title, [1]

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

Apresence: true

Bpresence true

Cpresence => true

Dpresence = true

Attempts:

3 left

💡 Hint

Common Mistakes

Using spaces instead of colon

Using => which is old hash rocket syntax but not preferred here

Using equals sign which is invalid

The correct syntax uses a symbol key and colon: presence: true.

4fill in blank

hard

Fill both blanks to add presence validation for :username and a custom error message.

Ruby on Rails

validates :username, [1]: true, message: [2]

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

Apresence

B"can't be blank"

C"must be present"

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using length instead of presence

Not quoting the error message string

Use presence: true to validate presence and provide a custom message string.

5fill in blank

hard

Fill all three blanks to validate presence of :password with allow_nil false and a custom message.

Ruby on Rails

validates :password, [1]: true, [2]: false, message: [3]

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

Apresence

Ballow_nil

C"can't be empty"

Dallow_blank

Attempts:

3 left

💡 Hint

Common Mistakes

Using allow_blank instead of allow_nil

Not quoting the message string

Setting allow_nil to true which disables presence validation

This code validates presence, disallows nil values, and sets a custom error message.

Practice

1. What does validates :name, presence: true do in a Rails model?

easy

A. It ensures the name field is not empty before saving.

B. It automatically fills the name field with a default value.

C. It deletes the record if name is empty.

D. It allows name to be empty without errors.

Solution

1. Step 1: Understand presence validation purpose

   Presence validation checks that a field is not blank before saving a record.

2. Step 2: Apply to name field

   Using validates :name, presence: true means the name must have a value.

3. Final Answer:

   It ensures the name field is not empty before saving. -> Option A

4. Quick Check:

   Presence validation = field not empty [OK]

Hint: Presence validation means field cannot be blank [OK]

Common Mistakes:

• Thinking it fills default values automatically
• Confusing presence with uniqueness validation
• Assuming it deletes records if empty

2. Which of the following is the correct syntax to add presence validation for the email attribute in a Rails model?

easy

A. validates_presence_of email

B. validates :email, presence: true

C. validate :email, presence: true

D. validates :email, required: true

Solution

1. Step 1: Recall modern Rails validation syntax

   Rails uses validates :attribute, presence: true for presence validation.

2. Step 2: Check each option

   validates_presence_of email is invalid syntax (missing symbol ":email"); validates :email, presence: true is the correct modern syntax; validate :email, presence: true is incorrect method name; validates :email, required: true uses wrong option key.

3. Final Answer:

   validates :email, presence: true -> Option B

4. Quick Check:

   Use validates :field, presence: true [OK]

Hint: Use validates :field, presence: true for presence [OK]

Common Mistakes:

• Using validate instead of validates
• Using required instead of presence
• Confusing old and new syntax

3. Given this model code:

class User < ApplicationRecord
  validates :username, presence: true
end

What happens if you try to save User.new(username: '')?

medium

A. The save fails because username is blank.

B. The user is saved with an empty username.

C. An error is raised due to syntax error.

D. The username is automatically set to 'default'.

Solution

1. Step 1: Understand presence validation effect on blank string

   Presence validation treats empty strings as invalid, so saving fails.

2. Step 2: Apply to username: ''

   Since username is empty string, validation fails and save returns false.

3. Final Answer:

   The save fails because username is blank. -> Option A

4. Quick Check:

   Empty string fails presence validation [OK]

Hint: Empty string fails presence validation, save returns false [OK]

Common Mistakes:

• Thinking empty string passes presence validation
• Expecting automatic default value assignment
• Confusing validation failure with exceptions

4. Identify the error in this model validation code:

class Product < ApplicationRecord
  validates :title, presence
end

medium

A. No error, code is correct.

B. Should use validate instead of validates.

C. The attribute title must be a string.

D. Missing true after presence.

Solution

1. Step 1: Check presence validation syntax

   Presence validation requires presence: true, not just presence.

2. Step 2: Identify missing true

   The code misses : true after presence, causing syntax error.

3. Final Answer:

   Missing true after presence. -> Option D

4. Quick Check:

   Presence validation needs presence: true [OK]

Hint: Always write presence: true for presence validation [OK]

Common Mistakes:

• Omitting : true after presence
• Using validate instead of validates
• Assuming attribute type affects validation syntax

5. You want to ensure a Post model's title and content are present, but content can be blank if title is 'Draft'. Which validation setup achieves this?

hard

A. validates :title, presence: true
validates :content, presence: false, unless: -> { title == 'Draft' }

B. validates :title, presence: true
validates :content, presence: true, if: -> { title == 'Draft' }

C. validates :title, presence: true
validates :content, presence: true, unless: -> { title == 'Draft' }

D. validates :title, presence: true
validates :content, presence: false, if: -> { title == 'Draft' }

Solution

1. Step 1: Understand requirement for content

   Content must be present except when title is 'Draft'.

2. Step 2: Use conditional presence validation

   Use presence: true with unless condition to skip validation if title is 'Draft'.

3. Step 3: Check options

   validates :title, presence: true validates :content, presence: true, unless: -> { title == 'Draft' } correctly uses unless: -> { title == 'Draft' } to skip content presence validation when title is 'Draft'. Others misuse if or set presence false incorrectly.

4. Final Answer:

   validates :title, presence: true validates :content, presence: true, unless: -> { title == 'Draft' } -> Option C

5. Quick Check:

   Use unless to skip presence validation conditionally [OK]

Hint: Use unless to skip presence validation conditionally [OK]

Common Mistakes:

• Using if instead of unless for skipping validation
• Setting presence: false which disables validation
• Not combining validations properly