Why CRUD operations through models in Ruby on Rails? - Purpose & Use Cases

The Big Idea

What if you could manage your app's data with just a few simple commands instead of complex SQL?

The Scenario

Imagine building a web app where you manually write SQL queries everywhere to create, read, update, and delete data.

Every time you want to change a user's info, you write raw SQL in your controller or view.

The Problem

Writing SQL manually is slow and easy to mess up.

You might forget to sanitize inputs, causing security holes.

It's hard to keep track of all queries scattered across your code.

The Solution

Rails models let you handle data with simple Ruby methods instead of raw SQL.

This keeps your code clean, safe, and easy to maintain.

Before vs After

✗ Before

User.connection.execute("INSERT INTO users (name, email) VALUES ('Alice', '[e-mail]')")

✓ After

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

What It Enables

You can focus on your app's logic while Rails handles database details safely and efficiently.

Real Life Example

When a user signs up, you just call User.create with their info instead of writing SQL queries yourself.

Key Takeaways

Manual SQL is error-prone and scattered.

Rails models provide simple methods for CRUD operations.

This makes your code safer, cleaner, and easier to work with.

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