Rails Scopes

Rails scopes allow you to define pre-defined queries for your ActiveRecord models which can be reused across the application. Scopes can save you a lot of time and make your code more concise and readable.

Defining a Scope

Scopes are defined in the model using the scope method. The scope method takes a block where you can define your query using ActiveRecord query methods like where, order, etc.

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

In the above example, we have defined a scope called published which returns only the articles that are marked as published.

Using a Scope

Once a scope is defined, it can be used just like a regular ActiveRecord query method. For example, to get all the published articles, you can call the published scope on the Article model.

@articles = Article.published

You can also chain multiple scopes to narrow down the results.

@articles = Article.published.order(created_at: :desc)

Dynamic Scopes

Dynamic scopes are scopes that take arguments at runtime to customize the query. For example, let's say we want to define a scope that returns articles for a particular category.

class Article < ApplicationRecord
  scope :in_category, -> (category) { where(category: category) }
end

We can now use the in_category scope to get articles for a specific category.

@articles = Article.in_category('Technology')

Conclusion

Scopes are a powerful feature of Rails that can help you write DRY and concise code. By defining common queries as scopes, you can avoid repeating yourself and make your models more expressive.