CRUD operations through models in Ruby on Rails - Performance & Optimization

Performance: CRUD operations through models

MEDIUM IMPACT

This affects how quickly data changes reflect on the page and the server response time during create, read, update, and delete actions.

Performing database updates inside a loop without batching

Ruby on Rails

Model.where(id: records.map(&:id)).update_all(attribute: new_value)

This sends a single query to update all records at once, reducing database calls and speeding response.

📈 Performance Gainsingle database query; reduces server processing time significantly

Performing database updates inside a loop without batching

Ruby on Rails

records.each do |record|
  record.update(attribute: new_value)
end

This triggers a separate database query for each record, causing many round-trips and slowing response.

📉 Performance Costblocks rendering for multiple milliseconds per query; triggers many server requests

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Multiple individual updates in loop	Minimal DOM changes but delayed	0 (server-side delay)	Low paint cost but delayed update	[X] Bad
Batch update_all query	Minimal DOM changes but faster	0 (server-side delay)	Low paint cost with faster update	[OK] Good

Rendering Pipeline

CRUD operations through models affect the server response time, which delays when the browser receives updated HTML or JSON. This impacts the time before the user sees updated content or can interact again.

→Server Processing

→Network Transfer

→DOM Update

⚠️ BottleneckServer Processing due to multiple or inefficient database queries

Core Web Vital Affected

INP

This affects how quickly data changes reflect on the page and the server response time during create, read, update, and delete actions.

Optimization Tips

1Avoid updating records one by one; batch updates reduce server queries.

2Minimize callbacks during bulk operations to speed up processing.

3Use efficient queries to reduce server response time and improve interaction speed.

Performance Quiz - 3 Questions

What is the main performance problem with updating records one by one in a loop?

A It causes many separate database queries, increasing server response time.

B It causes the browser to repaint multiple times unnecessarily.

C It increases the size of the HTML sent to the browser.

D It causes layout shifts on the page.

DevTools: Network

How to check: Open DevTools, go to Network tab, perform the CRUD action, and observe the number and duration of requests to the server.

What to look for: Look for multiple similar requests indicating inefficient queries or a single quick request indicating optimized batch operations.

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