How to schedule tasks using cron expressions in GitHub Actions: By defining a cron schedule in the workflow YAML file, we can automate the execution of tasks at specific intervals. For instance, setting */5 * * * * in the cron expression triggers the workflow every 5 minutes. Monitoring workflow runs in the "Actions" tab of the GitHub repository allows to verify that the scheduled tasks are executing as intended. #cronjobs #workflowautomation

When terraform state file is locked and you are unable to acquire a state lock, you can use terraform force-unlock <LOCK_ID> to forcefully remove the lock. #terrafrom

Use git reset --mixed HEAD~1 command to undo your last commit without losing the changes made in your last commit.

#git #gitReset #github

In TypeScript interfaces, ?: denotes optional properties. Here's an example:

interface User {
    name: string;
    age?: number; // Optional
}

const user1: User = { name: "Joe Mama" }; // Age is optional
const user2: User = { name: "Tony", age: 30 };

console.log(user1); // Output: { name: "Joe Mama" }
console.log(user2); // Output: { name: "Tony", age: 30 }

#javascript #typescript

Utility Types: TypeScript's Utility Types simplify complex type manipulations. For instance, Partial<T> makes all properties of type T optional

interface User {
    id: number;
    name: string;
    email: string;
}

function displayUser(user: Partial<User>) {
    console.log(user);
}

displayuser({ name: "Joe Mama" }); // Partial<T> will make the properties optional hence this is valid

#javascript #typescript

EAGER LOADING

Eager loading in Rails is a technique used to optimize database queries by loading associated records of the objects returned by the query, thereby reducing the number of database calls. This is particularly useful when you have associations defined in your models and you want to avoid the "N+1 query problem."

What is the N+1 Query Problem?

“N+1 Queries” are a very common cause of repeated queries in Rails applications. This happens when you make a request for a single row in one table, and then make an additional request per element in a has_many relationship, usually in a loop. Here’s an example:

Consider two models: Author and Book, where an Author has many Books.

class Author < ApplicationRecord 
  has_many :books 
 end 

class Book < ApplicationRecord 
  belongs_to :author 
end 

Scenario Without Eager Loading When you fetch authors and then access their books, Rails performs an additional query for each author to get their books.

# Fetching all authors and their books 
authors = Author.all 

authors.each do |author| 
  puts author.books.pluck(:title) 
end 

This will result in one query to fetch the authors and multiple queries to fetch books for each author, leading to the N+1 query problem.

How Eager Loading Works

Eager loading addresses this problem by loading all the necessary data in as few queries as possible, usually through the use of includes, eager_load, or preload.

Using Eager Loading with includes

To avoid the N+1 query problem, you can use includes to preload the associated books when fetching authors.

# Fetching all authors and their books with eager loading 
authors = Author.includes(:books) 

authors.each do |author| 
  puts author.books.pluck(:title) 
end 

With includes, Rails performs a single query to fetch all authors and another single query to fetch all associated books.

Using Eager Loading with eager_load

eager_load forces Rails to use a SQL JOIN to load the associated records. This can be useful if you need to filter or sort based on the associated records.

# Fetching all authors and their books with eager loading using JOIN 
authors = Author.eager_load(:books) 

authors.each do |author| 
  puts author.books.pluck(:title) 
end 

This approach performs a single query with a LEFT OUTER JOIN.

Using Eager Loading with preload

preload is similar to includes, but it always uses separate queries for loading the associations.

# Fetching all authors and their books with eager loading using separate queries 
authors = Author.preload(:books) 

authors.each do |author| 
  puts author.books.pluck(:title) 
end 

preload is useful when you know that separate queries will be more efficient, for example, when fetching a large number of records.

Summary

Eager loading is a powerful tool in Rails that helps to optimize database access by pre-loading associations. Using includes, eager_load, or preload appropriately can significantly improve the performance of your application by reducing the number of database queries.

#rails #db #optimizing_queries

Scoped Associations with Joins

Let's consider the following models: • Author with attributes id, name • Book with attributes id, title, published, author_id The association is that an Author has many Books, and a Book belongs to an Author.

Defining Scoped Associations First, let's define a scope on the Book model to filter only published books:

class Book < ApplicationRecord 
  belongs_to :author 
  scope :published, -> { where(published: true) } 
end 

Next, let's use this scope in the Author model to create a scoped association:

class Author < ApplicationRecord 
  has_many :books 
  has_many :published_books, -> { published }, class_name: 'Book' 
end 

Now, Author has an association called published_books, which only includes books that are published.

Using Scoped Associations with Joins

We can now use the scoped association in joins to fetch authors and their published books. Example 1: Fetch Authors with Published Books To fetch authors along with their published books:

@authors_with_published_books = Author.joins(:published_books).select('authors.*, books.title as book_title') 

This query joins the authors table with the books table but only includes books that are published, thanks to the scoped association published_books.

As a result, each Author object in @authors_with_published_books will have: • All attributes of the Author model. • An additional attribute called book_title representing the title of each associated book. #rails #scoped_associations_with_joins

Scoped associations

Let's say we have two models: User and Post. And we want to get all posts for user. We can do this:

class User < ActiveRecord::Base
  has_many :posts
end

class Post < ActiveRecord::Base
  belongs_to :user
end

user = User.first
user.posts

But what if we don't ever want to include posts for user which are published? Often I see people doing this:

class User < ActiveRecord::Base
  has_many :posts
end

class Post < ActiveRecord::Base
  belongs_to :user

  scope :published, -> { where(published: true) }
end

user = User.first
user.posts.published

And this is fine, but you can somehow forget to add published scope to your query. And then you will get all posts, even unpublished. And this is not what you want. Some people use default_scope for this, but it is not good idea. So what we can do? We can use scope in association:

class User < ActiveRecord::Base
  has_many :posts, -> { published }
  has_many :not_published_posts, -> { not_published }
end

class Post < ActiveRecord::Base
  belongs_to :user

  scope :published, -> { where(published: true) }
  scope :not_published, -> { where(published: false) }
end

user = User.first
user.posts # only published posts here

#rails #database #model #associations

There are two ways to call respond_to: Either we can pass it as a list of symbols or pass a block Block Version:

def index
  @people = Person.all

  respond_to do |format|
    format.json { render json: @people}
    format.xml { render xml: @people }
    format.html { render :index}
  end
end

Symbol version:

def index
  @people = Person.all
  respond_to :json, :xml, :html  
end

#respondto #actionview #rails

kubectl rollout restart deployment <deployment-name> command used to restart pods managed by a Kubernetes deployment without making any modifications to the deployment configuration. #devops #Kubernetes #rollingrestart