Uniqueness validation in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a uniqueness validation for the username attribute in a Rails model.

Ruby on Rails

validates :username, [1]: true

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

Auniqueness

Bpresence

Clength

Dnumericality

Attempts:

3 left

💡 Hint

Common Mistakes

Using presence instead of uniqueness will only check if the field is filled.

Using length or numericality does not check uniqueness.

The uniqueness option ensures that the username is unique in the database.

2fill in blank

medium

Complete the code to make the uniqueness validation case insensitive.

Ruby on Rails

validates :email, uniqueness: { [1]: false }

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

Acase_sensitive

Bcase_insensitive

Cignore_case

Dcase_sensitive_option

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent option like case_insensitive.

Setting case_sensitive to true does not ignore case.

Setting case_sensitive: false makes the uniqueness check ignore case differences.

3fill in blank

hard

Fix the error in the uniqueness validation syntax.

Ruby on Rails

validates :nickname, uniqueness: [1]

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

Atrue

Bfalse

C{ case_sensitive: false }

Dnil

Attempts:

3 left

💡 Hint

Common Mistakes

Passing true or false directly when options are needed.

Passing nil causes an error.

The uniqueness validation can take a hash of options. Using { case_sensitive: false } is correct syntax.

4fill in blank

hard

Fill both blanks to add a uniqueness validation scoped to the :account_id attribute.

Ruby on Rails

validates :email, uniqueness: { [1]: :account_id, [2]: false }

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

Ascope

Bcase_sensitive

Cunique

Dignore_case

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect option names like unique or ignore_case.

Mixing up the order of options.

The scope option limits uniqueness to the given attribute, and case_sensitive controls case sensitivity.

5fill in blank

hard

Fill all three blanks to add a uniqueness validation with a custom error message and case insensitivity.

Ruby on Rails

validates :username, uniqueness: { [1]: false, [2]: "[3]" }

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

Acase_sensitive

Bmessage

Chas already been taken

Dscope

Attempts:

3 left

💡 Hint

Common Mistakes

Using scope instead of message for the error text.

Not setting case_sensitive to false for case insensitivity.

Set case_sensitive: false to ignore case, and use message to customize the error text.

Practice

1. What does validates :email, uniqueness: true do in a Rails model?

easy

A. Deletes duplicate email records from the database

B. Prevents saving records with duplicate email values

C. Allows multiple records with the same email

D. Automatically encrypts the email field

Solution

1. Step 1: Understand uniqueness validation purpose

   Uniqueness validation ensures no two records have the same value for the specified field.

2. Step 2: Apply to the email field

   Using validates :email, uniqueness: true means Rails will check that the email is unique before saving.

3. Final Answer:

   Prevents saving records with duplicate email values -> Option B

4. Quick Check:

   Uniqueness validation = prevents duplicates [OK]

Hint: Uniqueness validation stops duplicate field values [OK]

Common Mistakes:

• Thinking it encrypts data
• Assuming it deletes duplicates automatically
• Believing it allows duplicates

2. Which is the correct syntax to add uniqueness validation for a username in a Rails model?

easy

A. validates :username, unique: true

B. validate :username, uniqueness: true

C. validates :username, uniqueness: true

D. validates_uniqueness_of :username, true

Solution

1. Step 1: Recall Rails validation syntax

   Rails uses validates :field, uniqueness: true for uniqueness validation.

2. Step 2: Check each option

   validates :username, uniqueness: true matches the correct syntax exactly; others have syntax errors or deprecated style.

3. Final Answer:

   validates :username, uniqueness: true -> Option C

4. Quick Check:

   Correct uniqueness syntax = validates :field, uniqueness: true [OK]

Hint: Use 'validates :field, uniqueness: true' syntax [OK]

Common Mistakes:

• Using 'unique' instead of 'uniqueness'
• Using 'validate' instead of 'validates'
• Using deprecated 'validates_uniqueness_of' syntax incorrectly

3. Given this model code:

class User < ApplicationRecord
  validates :email, uniqueness: true
end

What happens if you try to save two users with the same email?

medium

A. The second user fails to save due to validation error

B. Both users save successfully

C. An exception is raised immediately

D. The database automatically rejects the second user

Solution

1. Step 1: Understand Rails validation behavior

   Uniqueness validation runs before saving and prevents duplicates by adding errors.

2. Step 2: Effect on saving duplicate email

   The first user saves fine; the second user triggers validation failure and does not save.

3. Final Answer:

   The second user fails to save due to validation error -> Option A

4. Quick Check:

   Uniqueness validation blocks duplicates on save [OK]

Hint: Second duplicate save triggers validation error [OK]

Common Mistakes:

• Thinking both save successfully
• Expecting a database exception instead of validation error
• Assuming database rejects without validation

4. Identify the problem in this model code:

class Product < ApplicationRecord
  validates :code, uniqueness: true
  validates :code, presence: true
end

Why might duplicates still be saved?

medium

A. Uniqueness validation is case sensitive by default

B. Presence validation conflicts with uniqueness validation

C. The validations are in the wrong order

D. No unique index exists in the database for code

Solution

1. Step 1: Understand validation vs database constraints

   Rails validations check before saving but do not guarantee uniqueness at the database level.

2. Step 2: Check for unique index necessity

   Without a unique database index on code, race conditions can allow duplicates.

3. Final Answer:

   No unique index exists in the database for code -> Option D

4. Quick Check:

   Validation alone can't prevent duplicates without DB index [OK]

Hint: Add unique DB index to fully prevent duplicates [OK]

Common Mistakes:

• Assuming validations alone guarantee uniqueness
• Confusing presence and uniqueness validations
• Thinking validation order matters here

5. You want to ensure usernames are unique but case insensitive (e.g., 'User1' and 'user1' count as duplicates). How do you write the validation?

hard

A. validates :username, uniqueness: { case_sensitive: false }

B. validates :username, uniqueness: true, case_sensitive: false

C. validates :username, unique: { case_sensitive: false }

D. validates_uniqueness_of :username, case_sensitive: true

Solution

1. Step 1: Recall uniqueness validation options

   To make uniqueness case insensitive, use uniqueness: { case_sensitive: false }.

2. Step 2: Check each option's correctness

   validates :username, uniqueness: { case_sensitive: false } uses correct syntax and option key; others have syntax errors or wrong case sensitivity.

3. Final Answer:

   validates :username, uniqueness: { case_sensitive: false } -> Option A

4. Quick Check:

   Case insensitive uniqueness = uniqueness: { case_sensitive: false } [OK]

Hint: Use uniqueness with case_sensitive: false for case insensitivity [OK]

Common Mistakes:

• Placing case_sensitive outside uniqueness hash
• Using 'unique' instead of 'uniqueness'
• Setting case_sensitive to true by mistake