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# What are macros?

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In Ruby on Rails, macros are methods that generate other methods or code. They are often used to define associations, validations, and other behaviors in a declarative way. Macros help in writing cleaner and more readable code by abstracting repetitive tasks.

Common Macros in Rails

Associations: Macros like has_many, belongs_to, and has_one are used to define relationships between models.
class User < ApplicationRecord
  has_many :posts
  belongs_to :account
end
Validations: Macros like validates are used to ensure data integrity.

class User < ApplicationRecord
  validates :email, presence: true, uniqueness: true
end
Callbacks: Macros like before_save, after_create, etc., are used to define callbacks.

class User < ApplicationRecord
  before_save :normalize_name

  private

  def normalize_name
    self.name = name.downcase.titleize
  end
end
How Macros Work

Macros are essentially class-level methods that define behaviour for instances of the class. When you use a macro, it dynamically generates methods and other code that gets executed when the class is loaded.

Example:

class User < ApplicationRecord
  has_many :posts
end
The has_many :posts macro generates methods like posts, posts.build, and posts.create for the User class, allowing you to interact with associated Post objects easily.

Creating Custom Macros

You can also create your own macros in Rails. Here’s a simple example of a custom macro that adds a class method to log messages:

module Loggable
  def log_message(message)
    define_method(:log) do
      puts message
    end
  end
end

class ApplicationRecord < ActiveRecord::Base
  extend Loggable
end

class User < ApplicationRecord
  log_message "User created!"
end

user = User.new
user.log  # Output: User created!
Macros in Rails make it easier to write DRY (Don’t Repeat Yourself) code by encapsulating common patterns and behaviours into reusable methods.