Solving the N+1 Query Problem with Rails' includes Method
2 min read
This article was written with the help of AI.
When working with Rails, you've likely encountered the N+1 query problem. This occurs when you have a database query that returns N records, and then you loop through those records and execute a separate query for each one. This can result in a large number of queries being executed, which can slow down your application.
Fortunately, Rails provides a solution to this problem in the form of the
includes method. The
includes method allows you to load associated records in a single query, rather than querying the database for each record individually.
Here's an example of how you can use
includes in Rails:
class Post < ApplicationRecord belongs_to :author has_many :comments end class Author < ApplicationRecord has_many :posts end class Comment < ApplicationRecord belongs_to :post end
In this example, a post belongs to an author and has many comments. Now, let's say we want to display a list of posts and their authors and comments. We could do this with the following code:
@posts = Post.all @posts.each do |post| puts post.title puts post.author.name post.comments.each do |comment| puts comment.body end end
This code will work, but it will result in N+1 queries being executed - one query to load all the posts, and then one query for each post to load its associated author and comments.
To solve this problem, we can use the
includes method to preload the associated records:
@posts = Post.includes(:author, :comments).all @posts.each do |post| puts post.title puts post.author.name post.comments.each do |comment| puts comment.body end end
includes, we can load all the posts, their associated authors, and their associated comments in a single query, rather than querying the database for each record individually. This can significantly improve the performance of our application, especially when dealing with large datasets.
In addition to
includes also supports
So, the next time you encounter the N+1 query problem in Rails, remember to use the
includes method to preload the associated records and improve the performance of your application.