This article will discuss two important concepts in Ruby on Rails - Named Scopes and Default Scopes. The main idea is to get results based on some condition.
Named Scopes
Let’s say we have a model named Post that has columns title, body and author and is_published with title, body and author as string and is_published as boolean.
Assume we want to get only those posts that are published. In app/models/post.rb:
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# app/models/post.rb
scope :published, lambda { where(is_published: true) }
Now hit the following scope:
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Post.published
This will generate the following query:
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SELECT "posts".* FROM "posts" WHERE "posts"."is_published" = $1 LIMIT $2 [["is_published", true], ["LIMIT", 11]]
Default Scopes
There is another use case where we want only published posts even if we hit Post.all method. Here, default scopes come in.
In app/models/post.rb.
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# app/models/post.rb
default_scope { where(is_published: true) }
Now get all the posts.
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Post.all
This will generate the following query:
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SELECT "posts".* FROM "posts" WHERE "posts"."is_published" = $1 LIMIT $2 [["is_published", true], ["LIMIT", 11]]
Now you know how to utilize Named Scopes and Default Scopes in your Ruby on Rails applications!