CRUD operations through models in Ruby on Rails - Mini Project: Build & Apply

CRUD Operations Through Models in Rails

📖 Scenario: You are building a simple Rails app to manage a list of books in a library. Each book has a title and an author.

🎯 Goal: Learn how to create, read, update, and delete book records using Rails models.

📋 What You'll Learn

Create a Book model with title and author attributes

Add a variable to hold a sample book's title

Use the Book model to create a new book record

Update the book's author and then delete the book record

💡 Why This Matters

🌍 Real World

Managing data records like books, users, or products is common in web apps. Rails models make it easy to create, read, update, and delete these records.

💼 Career

Understanding CRUD operations through models is essential for backend Rails developers to handle database interactions cleanly and efficiently.

1

Create the Book model with attributes

Create a Rails model called Book with string attributes title and author using rails generate model Book title:string author:string.

Ruby on Rails

# Run the rails generate command to create the Book model
# Your code here

Hint

Use the Rails generator to create a model with the exact attribute names title and author.

2

Add a variable for a sample book title

In the Rails console or a Ruby file, create a variable called sample_title and set it to the string 'The Great Gatsby'.

Ruby on Rails

# Create a variable sample_title with value 'The Great Gatsby'
# Your code here

Hint

Assign the exact string 'The Great Gatsby' to the variable sample_title.

3

Create a new Book record using the model

Use the Book.create method to create a new book with title set to sample_title and author set to 'F. Scott Fitzgerald'.

Ruby on Rails

sample_title = 'The Great Gatsby'

# Create a new Book record with title sample_title and author 'F. Scott Fitzgerald'
# Your code here

Hint

Use Book.create with a hash of attributes for title and author.

4

Update and delete the Book record

Update the author of the book variable to 'Francis Scott Fitzgerald' using update. Then delete the book record using destroy.

Ruby on Rails

sample_title = 'The Great Gatsby'

book = Book.create(title: sample_title, author: 'F. Scott Fitzgerald')

# Update book author to 'Francis Scott Fitzgerald'
# Then delete the book record
# Your code here

Hint

Use update on the book object to change the author, then call destroy to remove it.

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