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: Oct 6, 2025
Author: Syed Sibtain
System Analyst

The Problem: When comparing images for UI testing, we needed to implement a fuzz factor to ignore small colour differences (like anti-aliasing, compression artifacts, or minor rendering variations). This is crucial for UI screenshots where a 1-2 pixel difference shouldn't count as a "failure."

Command Line approach

Code

# This works but is fragile
magick compare -metric AE -fuzz 10% image1.png image2.png NULL: 2>&1

# Problems:
# - Shell command parsing issues
# - Error handling is difficult
# - Output parsing is brittle
# - Cross-platform compatibility issues
# - Hard to debug when things go wrong

The Mini Magick Solution

Code

# Step 1: Create difference image
difference_image = first_image.composite(second_image) do |c|
  c.compose "difference"
end

# Step 2: Apply fuzz factor using threshold
thresholded_diff = difference_image.dup
thresholded_diff.combine_options do |c|
  c.normalize
  c.threshold "10%"
# This acts as our fuzz factor!
end

# Step 3: Get statistics
mean_value = thresholded_diff.identify do |c|
  c.format "%[fx:mean]"
end

# Step 4: Convert to percentage
percentage = mean_value.to_f * 100

Key Insight: Fuzz Factor = Threshold
- In ImageMagick: fuzz 10% tells it to ignore differences below 10%
- In MiniMagick: threshold10% does the same thing by setting pixels below 10% to black

#ruby #image

Published: Sep 30, 2025
Author: Syed Sibtain
System Analyst

* The Problem:* I had an existing Elixir app with a users table that used password_digest field, but Devise expects encrypted_password by default.

Devise's Default Password Field:

Code

# Devise expects this by default:
class User < ApplicationRecord
  devise :database_authenticatable
  # Uses 'encrypted_password' column automatically
end

Our Existing Schema:

Code

# Uses password_digest
create_table :users do |t|
  t.string :password_digest, null: false  # ← Different field name!
  # ... other fields
end

The Override Solution:

Code

# Devise calls: user.encrypted_password
# Our override returns: user.password_digest

class User < ApplicationRecord
  devise :database_authenticatable, :registerable, :validatable

  # Tell Devise to use our existing password_digest field
  def self.encrypted_password_column
    :password_digest
  end

  # Override the getter method
  def encrypted_password
    read_attribute(:password_digest)
  end

  # Override the setter method  
  def encrypted_password=(value)
    self.password_digest = value
  end
end

So we can simply override Devise's password field by:
1. Telling Devise which column to use (encrypted_password_column)
2. Creating getter/setter bridges (encrypted_password methods)
3. Using read_attribute to avoid method conflicts
#devise #auth

Published: Sep 30, 2025
Author: Syed Sibtain
System Analyst

What does model: resource actually do in form_with?

model: resource is the bridge between our form and the data object. It makes forms smart - they remember values, show errors, and handle the complex Rails form lifecycle automatically.

Example:

Code

<%= form_with model: resource, as: resource_name, url: session_path(resource_name), local: true, class: "space-y-6" do |f| %>

model: resource tells Rails:
• Which object to bind the form to
• Where to get field values from
• Where to send validation errors to
• What HTTP method to use (POST for new, PATCH for existing)
In Devise Context:
resource is a Devise helper that returns:
• New User object (for signup) - User.new
• New User object (for signin) - User.new (usually empty, not pre-populated)
Without model: resource:
• Form fields are always empty
• No automatic error handling
• Manual parameter naming required
• No automatic HTTP method detection
#CU6U0R822 #devise

Published: Sep 30, 2025
Author: Satya

To understand network sockets locally, you can try this simple demo with two terminal tabs:
1. In the first tab run ns -l 1234 : This starts a small server process that listens for TCP connections on your computer’s address (localhost / 127.0.0.1) at port 1234.
2. In the second tab run ns localhost 1234 : This connects a client to the server on 127.0.0.1:1234 , creating a TCP connection between the two processes.
Now type text in one terminal and press Enter you’ll see the same text appear in the other terminal and vice-versa. 🚀

#sockets

Published: Sep 24, 2025
Author: Ashwani Kumar Jha
Senior System Analyst

Filtering API logs with path params in OpenSearch

When querying logs in OpenSearch Dashboards, paths with dynamic segments (like IDs) often don’t match with the usual search bar syntax because the field is mapped as text instead of keyword.

Problem:
• Queries like

Code

json.req.url: "/api/bankAccounts/*/debit"

return no results.
• .keyword may not exist (json.req.url.keyword) if the field wasn’t mapped that way at ingestion.
Solution:
Use Query DSL with a wildcard or regexp query.

✅ Wildcard query (matches any value in the middle):

Code

{
  "query": {
    "wildcard": {
      "json.req.url": {
        "value": "/api/bankAccounts*/debit"
      }
    }
  }
}

✅ Regex query (restricts the middle part to numbers):

Code

{
  "query": {
    "regexp": {
      "json.req.url": "/api/bankAccounts/[0-9]+/debit"
    }
  }
}

#opensearch #logs

Published: Sep 24, 2025
Author: Mohammad hussain
System Analyst

You can mark methods as deprecated in Rails using ActiveSupport::Deprecation. This warns developers that a method will be removed in future versions.

Code

class User < ApplicationRecord
  def full_name
    "#{first_name} #{last_name}"
  end

  # Mark full_name as deprecated
  deprecate :full_name, deprecator: ActiveSupport::Deprecation.new("2.0", "MyApp")
end

Code

DEPRECATION WARNING: full_name is deprecated and will be removed from MyApp 2.0

💡 Might be especially useful in larger codebases, where many developers might be using the same method and you want to safely signal that it will be removed without breaking things immediately.
#Rails

Published: Sep 19, 2025
Author: Nived Hari
System Analyst

In Prisma, there’s a big difference between directly setting a foreign key and using connect when creating related records.

Code

// ❌ Directly setting the foreign key
users: {
  create: {
    userId: testUser.id,
  },
}

// ✅ Using relation API
users: {
  create: {
    user: {
      connect: { id: testUser.id },
    },
  },
}

• Direct assignment just writes the raw foreign key value — Prisma doesn’t check if the user actually exists.
• connect uses Prisma’s relation API, validates that the record exists, and safely links them.

#prisma

Published: Sep 17, 2025
Author: Ashwani Kumar Jha
Senior System Analyst

Nx has a built-in command to remove libraries

Nx provides the @nx/workspace:remove generator that can remove a library from our workspace.

The command:

Code

npx nx g @nx/workspace:remove

What it does automatically:
• Deletes the library folder and all its files
• Removes the project from nx.json and workspace configuration
• Checks for dependencies and warns if other projects still use it
We can use --forceRemove flag if we want to remove a library even when other projects depend on it (though this can break the build).
#nx #monorepo

Published: Sep 2, 2025
Author: Nived Hari
System Analyst

WITH (NOLOCK) is often used to speed up queries by avoiding shared locks, which means the query won’t block other reads or writes. This can improve performance on busy systems, but it comes at the cost of data accuracy.

When using NOLOCK, SQL Server may:
• Read uncommitted (dirty) data that could later be rolled back.
• Return missing or duplicate rows due to page splits and concurrent writes.
• Show inconsistent values within the same row if columns are updated mid-read.
In short: NOLOCK trades reliability for speed. It’s fine for dashboards, reports, or monitoring where approximate numbers are acceptable, but it should be avoided for financial or critical business logic where accuracy is essential.

#sql

Published: Sep 2, 2025
Author: Sudeep Hipparge

Prisma --create-only

npx prisma migrate dev --create-only --name <migration_name>

Creates a migration file with the SQL changes but does not apply them to the database.

Why this is useful:

✅ Safe inspection – lets you review the generated SQL before running it, especially helpful for destructive operations like drops or PK changes.

✅ Manual adjustments – you can tweak the SQL (e.g., add a USING clause for type casting or backfill data before dropping a column).

✅ Separation of responsibilities – you can generate migrations while DBAs/ops review and apply them in controlled environments.

Key takeaway:

👉 --create-only is like a dry run for migration generation – you get the recipe, but the dish isn't cooked yet 🍳.

#postgres

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