TILs - Fueling Curiosity, One Insight at a Time

At Codemancers, we believe every day is an opportunity to grow. This section is where our team shares bite-sized discoveries, technical breakthroughs and fascinating nuggets of wisdom we've stumbled upon in our work.

Published
Author
user-image
Adithya Hebbar
System Analyst
Updating Session in NextAuth

In NextAuth, you can update the session data using the update function from useSession(). Here's how you can modify user details dynamically:

Code

const { data: session, update } = useSession();

await update({
  user: {
    ...session?.user,
    name: "Updated Name",
    role: "editor", 
  },
});


Assuming a strategy: "jwt" is used, the update() method will trigger a jwt callback with the trigger: "update" option. You can use this to update the session object on the server.


Code

export default NextAuth({
  callbacks: {
    // Using the `...rest` parameter to be able to narrow down the type based on `trigger`
    jwt({ token, trigger, session }) {
      if (trigger === "update" && session?.name) {
        // Note, that `session` can be any arbitrary object, remember to validate it!
        token.name = session.name
        token.role = session.role
      }
      return token
    }
  }
})


This updates the session without requiring a full reload, ensuring the UI reflects the changes immediately. 🚀

#next-auth #nextjs
Published
Author
user-image
Puneeth kumar
System Analyst
Traits in FactoryBot helps to define reusable variations of a factory without creating multiple factories. They are useful when we need optional attributes or specific states in test data.
Let's say we have a User model with different roles (admin, regular, guest). Instead of writing separate factories, we can use traits like below:

Code

# spec/factories/users.rb
FactoryBot.define do
  factory :user do
    first_name { Faker::Name.first_name }
    email { Faker::Internet.unique.email }
    password { "password123" }

    trait :admin do
      role { "admin" }
    end

    trait :guest do
      role { "guest" }
    end

    trait :confirmed do
      confirmed_at { Time.current }
    end
  end
end


And use it like below

Code

let(:admin_user) { create(:user, :admin) }
let(:guest_user) { create(:user, :guest) }
let(:confirmed_user) { create(:user, :confirmed) }


#CU6U0R822 #factory_bot
Published
Author
user-image
Nived Hari
System Analyst
In Ruby, public_send allows calling a method dynamically when its name is stored in a variable.

• Why Use public_send?
Instead of calling methods explicitly, we can determine the method name at runtime and call it dynamically.

Example: Handling Different Attribute Names

Code

quantity_field = item.respond_to?(:ordered_quantity) ? :ordered_quantity : :quantity
new_quantity = item.public_send(quantity_field).to_i + item_case[:quantity].to_i


• If item has ordered_quantity, it calls item.ordered_quantity
• Otherwise, it calls item.quantity
• This avoids unnecessary if-else statements
#ruby
Published
Author
user-image
Nived Hari
System Analyst
In Ruby, there are two ways to define hash keys:

1. Using the Colon Syntax (:) – Creates a Literal Symbol Key

Code

item.update!(
  ordered_quantity: new_quantity,
)


Key Behavior: The key is treated as a fixed symbol (e.g., :ordered_quantity).

2. Using the Hash Rocket (=>) – Evaluates the Left-Hand Side as a Key

Code

item.update!(
  quantity_field => new_quantity,
)


Key Behavior: The left-hand side is evaluated dynamically, making it useful for variable-based keys.

Example Use Case: Dynamic Keys

Code

quantity_field = item.respond_to?(:ordered_quantity) ? :ordered_quantity : :quantity
new_quantity = item.public_send(quantity_field).to_i + item_case[:quantity].to_i

item.update!(
  quantity_field => new_quantity,  # Evaluates to :ordered_quantity or :quantity
)


Here, quantity_field is determined dynamically based on the model, so => must be used instead of :.

When to Use =>?
• When working with multiple models that have different column names
• When dynamically generating hash keys at runtime
• When building flexible APIs that handle varying attribute names
Takeaway:
• Use : when the key is static and always the same.
• Use => when the key is stored in a variable or needs to be evaluated dynamically.
#ruby
Published
Author
user-image
Nived Hari
System Analyst
In Ruby, attr_reader automatically creates a getter method for instance variables, making code cleaner and more concise. Instead of writing:

Code

def some_number
  @some_number
end


You can simply use:

Code

attr_reader :some_number


This makes attributes read-only while keeping the class lightweight

#ruby #CU6U0R822
Published
Author
user-image
Nitturu Baba
System Analyst
Real-time AI response streaming improves user experience by reducing wait times and making interactions feel more dynamic. Instead of waiting for the entire response to be generated before displaying it, streaming allows data to be processed and presented incrementally.

Example of AI response streaming using Nest Js backend and Next JS front end.

Setting Up the NestJS Backend for Streaming AI Responses

Controller


Code

import { Controller, Post, Body, Res } from '@nestjs/common';
import { openai } from '@ai-sdk/openai';
import { streamText } from 'ai';
import { Response } from 'express';

@Controller('orchestrator')
export class OrchestratorController {

 @Post('chat')
 async chat(@Body() payload: any, @Res() res: Response) {
  const { messages } = payload;

  const result = streamText({
   model: openai('gpt-4o'),
   messages,
  });
   
  result.pipeDataStreamToResponse(res); // Streams the AI response directly to the client
 }
}


How It Works
• The @Post('chat') endpoint listens for chat requests.
• The streamText function sends user messages to OpenAI and receives a streamed response.
• pipeDataStreamToResponse(res) directly streams the AI-generated content to the client as it arrives.
Building the Next.js Frontend for AI Response Streaming

chat/page.tsx


Code

'use client';

import { useChat } from '@ai-sdk/react';

export default function Home() {
 const { messages, input, handleInputChange, handleSubmit } = useChat({
  api: 'https://localhost:3000/api/orchestrator/chat',  // make the post request to the NestJS backend
 });

 return (
  <div>
   {messages.map((message) => (
    <div key={message.id}>
     {message.role === 'user' ? 'User: ' : 'AI: '}
     {message.content}
    </div>
   ))}

   <form onSubmit={handleSubmit}>
    <input
     name="prompt"
     value={input}
     onChange={handleInputChange}
     className="text-black"
    />
    <button type="submit">Submit</button>
   </form>
  </div>
 );
}


How It Works
• The useChat hook from AI-SDK manages state and streaming logic automatically.
• It sends user messages to the backend and updates the UI in real time as responses arrive.
• The messages array dynamically updates, displaying each chunk of AI-generated text as it's received.
#C08DPTN3JAW #streaming #next js #nest js
Published
Author
user-image
Puneeth kumar
System Analyst
Collection caching is a way to speed up rendering multiple items on a page by storing their HTML in cache.
How it works:
1. When we use <%= render partial: 'products/product', collection: @products, cached: true %>, Rails checks if each product's HTML is already stored in the cache.
2. If a product’s HTML is found in the cache, Rails loads it quickly instead of rendering it again.
3. If a product’s HTML is not in the cache, Rails will render it, store it in the cache, and use it next time.
4. The big advantage: Rails fetches all cached products at once (instead of one by one), making it much faster.
#CU6U0R822 #caching #collection_caching
Published
Author
user-image
Nived Hari
System Analyst
When testing with Capybara, you might need to scroll an element into view before interacting with it. Instead of using JavaScript like:

Code

page.execute_script("arguments[0].scrollIntoView(true)", button)


You can use Capybara's built-in method:

Code

scroll_to(button)  # Scrolls to the element


This is available in
Capybara 3.26+
and is the preferred way to ensure visibility before clicking or interacting with an element.

#capybara #CU6U0R822 #C041BBLJ57G
Published
Author
user-image
Nived Hari
System Analyst
In JavaScript, you can use localeCompare with { sensitivity: "base" } to compare strings without considering case or accents.
Example:


Code

"Test".localeCompare("test", undefined, { sensitivity: "base" }) === 0; // ✅ True
"café".localeCompare("cafe", undefined, { sensitivity: "base" }) === 0; // ✅ True
"Hello".localeCompare("HELLO", undefined, { sensitivity: "base" }) === 0; // ✅ True


• Case-insensitive
• Accent-insensitive
No need for toLowerCase() hacks anymore! 🎉

second argument is locale . by giving it as "Undefined" it uses default locale of the runtime environment. We can specify as "en", "id" etc. It is used in sorting scenarios ig.

Sensitivity is the behaviour of the comparison


Code

"base" → Ignores case & accents ("café" == "cafe", "Hello" == "hello")

"accent" → Considers accents but ignores case ("café" != "cafe", "Hello" == "hello")

"case" → Considers case but ignores accents ("café" == "cafe", "Hello" != "hello")

"variant" → Considers both case & accents ("café" != "cafe", "Hello" != "he



#stimulus #JavaScript #StringComparison
Published
Author
user-image
Nived Hari
System Analyst
By default, Capybara only finds visible and interactable elements. If a button is disabled or outside the viewport, Capybara may fail to locate it.
To fix this, use:


Code

expect(page).to have_button("Add Discrepancy", disabled: true, visible: :all)


• disabled: true ensures the button is actually disabled
• visible: :all allows Capybara to find buttons that are hidden, off-screen, or disabled
This is useful when testing UI behaviors where buttons are conditionally enabled/disabled or require scrolling to be visible.

#CU6U0R822 #capybara #C041BBLJ57G #specs

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