CRUD operations through models in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new user record with name 'Alice'.

Ruby on Rails

user = User.[1](name: 'Alice')

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

Acreate

Bfind

Cupdate

Ddestroy

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'find' instead of 'create' to make a new record.

Using 'update' which changes existing records, not create new ones.

The create method creates and saves a new record in the database.

2fill in blank

medium

Complete the code to find a user by id 5.

Ruby on Rails

user = User.[1](5)

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

Adelete

Bnew

Ccreate

Dfind

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'new' which only initializes but does not fetch from database.

Using 'create' which makes a new record instead of finding.

The find method retrieves a record by its id.

3fill in blank

hard

Fix the error in updating a user's email to '[e-mail]'.

Ruby on Rails

user = User.find(3)
user.[1](email: '[e-mail]')

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

Aupdate

Bcreate

Cdestroy

Dfind

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'create' which makes a new record instead of updating.

Using 'destroy' which deletes the record.

The update method changes attributes and saves the record.

4fill in blank

hard

Fill both blanks to delete a user with id 7.

Ruby on Rails

user = User.[1](7)
user.[2]

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

Afind

Bcreate

Cdestroy

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to delete without finding the user first.

Using 'delete' instead of 'destroy' which is the Rails method.

First find the user, then call destroy to delete it.

5fill in blank

hard

Fill all three blanks to create a user, update their name, and then delete them.

Ruby on Rails

user = User.[1](name: 'Bob')
user.[2](name: 'Robert')
user.[3]

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

Acreate

Bupdate

Cdestroy

Dfind

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of operations.

Using 'find' instead of 'create' to make a new user.

Create a new user, update the name, then delete the user record.

Practice

1. Which Rails model method is used to add a new record to the database?

easy

A. create

B. find

C. update

D. destroy

Solution

1. Step 1: Understand CRUD operations

   CRUD means Create, Read, Update, Delete. Each operation has a matching Rails model method.

2. Step 2: Match method to action

   create adds a new record, find reads, update changes, and destroy deletes.

3. Final Answer:

   create -> Option A

4. Quick Check:

   Create = create [OK]

Hint: Create means adding new data, so use create [OK]

Common Mistakes:

• Confusing find with create
• Using update to add new records
• Trying to delete with create

2. Which of the following is the correct syntax to update a user's email in Rails?

easy

A. user.change(email = '[e-mail]')

B. user.update(email: '[e-mail]')

C. user.modify(email: '[e-mail]')

D. user.edit(email => '[e-mail]')

Solution

1. Step 1: Recall Rails update syntax

   The correct method to change attributes is update with a hash of attributes.

2. Step 2: Check syntax correctness

   user.update(email: '[e-mail]') uses symbol keys and colon, which is correct Ruby syntax.

3. Final Answer:

   user.update(email: '[e-mail]') -> Option B

4. Quick Check:

   Update syntax = user.update(hash) [OK]

Hint: Use update with symbol keys and colon for attributes [OK]

Common Mistakes:

• Using assignment (=) inside method arguments
• Using non-existent methods like change or modify
• Wrong hash syntax like email => instead of email:

3. Given the code:

user = User.find(1)
user.destroy
puts User.exists?(1)

What will be printed?

medium

A. An error

B. true

C. nil

D. false

Solution

1. Step 1: Understand what destroy does

   destroy deletes the record from the database permanently.

2. Step 2: Check if record exists after deletion

   User.exists?(1) returns false because the user with ID 1 was deleted.

3. Final Answer:

   false -> Option D

4. Quick Check:

   Destroy removes record, so exists? returns false [OK]

Hint: Destroy deletes record; check existence returns false after [OK]

Common Mistakes:

• Thinking destroy only marks record inactive
• Assuming exists? returns true after deletion
• Confusing destroy with delete (which skips callbacks)

4. Identify the error in this code snippet:

user = User.find_by(id: 10)
user.update(name: 'Alice')

medium

A. No error, code works fine

B. find_by should be find to work

C. find_by returns nil if no record found, so calling update on nil causes error

D. update method does not accept hash arguments

Solution

1. Step 1: Understand find_by behavior

   find_by returns nil if no matching record is found.

2. Step 2: Check method call on nil

   Calling update on nil causes a NoMethodError because nil has no update method.

3. Final Answer:

   find_by returns nil if no record found, so calling update on nil causes error -> Option C

4. Quick Check:

   Nil object has no update method [OK]

Hint: Check if find_by returns nil before calling methods [OK]

Common Mistakes:

• Assuming find_by always returns a record
• Thinking update cannot take hash arguments
• Confusing find and find_by behavior

5. You want to update multiple users' status to 'active' only if their current status is 'pending'. Which Rails code correctly does this in one query?

hard

A. User.where(status: 'pending').update_all(status: 'active')

B. User.update_all(status: 'active').where(status: 'pending')

C. User.find_each { |u| u.update(status: 'active') if u.status == 'pending' }

D. User.all.update(status: 'active') if User.status == 'pending'

Solution

1. Step 1: Filter users with status 'pending'

   User.where(status: 'pending') selects only users with 'pending' status.

2. Step 2: Update all selected users at once

   update_all(status: 'active') updates the status for all filtered users in one database query.

3. Final Answer:

   User.where(status: 'pending').update_all(status: 'active') -> Option A

4. Quick Check:

   Filter then update_all = efficient bulk update [OK]

Hint: Use where to filter, then update_all to bulk update [OK]

Common Mistakes:

• Calling update_all before filtering
• Using find_each which is slower for bulk updates
• Trying to chain where after update_all