CRUD operations through models in Ruby on Rails

Introduction

CRUD operations let you create, read, update, and delete data easily using models. Models connect your app to the database in a simple way.

When you want to add new records to your database, like adding a new user.

When you need to show data from the database, like listing all products.

When you want to change existing data, like updating a user's email.

When you want to remove data, like deleting a comment.

When you want to keep your code clean by using Rails models to handle data.

Syntax

Ruby on Rails

# Create
Model.create(attributes)

# Read
Model.find(id)
Model.where(condition)
Model.all

# Update
record = Model.find(id)
record.update(attributes)

# Delete
record = Model.find(id)
record.destroy

Use create to add new records quickly.

find raises an error if no record is found; where returns an empty collection if none match.

Examples

This creates a new user with name and email.

Ruby on Rails

User.create(name: "Alice", email: "[e-mail]")

This finds the user with ID 1.

Ruby on Rails

User.find(1)

This gets all users who are active.

Ruby on Rails

User.where(active: true)

This finds user 1 and updates their email.

Ruby on Rails

user = User.find(1)
user.update(email: "[e-mail]")

Sample Program

This example shows all CRUD steps: create a user, read it, update the name, then delete it. Finally, it checks if the user still exists.

Ruby on Rails

class User < ApplicationRecord
end

# Create a user
user = User.create(name: "Bob", email: "[e-mail]")

# Read the user
found_user = User.find(user.id)

# Update the user
found_user.update(name: "Bobby")

# Delete the user
found_user.destroy

puts User.exists?(user.id)

Important Notes

Always handle exceptions when using find to avoid app crashes if record is missing.

Use update to change only the fields you want.

destroy removes the record from the database permanently.

Summary

CRUD stands for Create, Read, Update, Delete.

Rails models make CRUD easy and clean.

Use model methods like create, find, update, and destroy to manage data.

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