Ruby: Query for N+1 queries problem

[asgerf]

No description provided.

[github-actions]

QHelp previews:

ruby/ql/src/queries/performance/ActiveRecordAssociationQueriedInLoop.qhelp

ActiveRecord association queried in loop

Performing database queries in a loop can be inefficient compared to performing a single query up front that retrieves all the data at once.

ORMs such as ActiveRecord implicitly query the database when certain members of an object are being accessed. But if such a member is accessed in a loop, it can result in a separate query for each iteration. ActiveRecord provides a way to eagerly load associated data using the includes method, which can be used to speed up such queries.

Recommendation

In ActiveRecord, use includes to eagerly load associated data that you expect to access in a loop.

Example

The following example code gets the names of all podcasts followed by a user:

def get_podcast_names(user):
    user.podcasts.map do |podcast|
        podcast.name
    end
end

However, the call to name inside the loop will result in a separate SQL query being executed to obtain the name. To speed this up, use includes to eagerly load the associated data:

def get_podcast_names(user):
    user.podcasts.includes(:name).map do |podcast|
        podcast.name
    end
end

Now all the associated podcast names are loaded up front with a single SQL query, and the call to name no longer results in a separate query.

References

• OWASP: SSRF
• OWASP: XSS Unvalidated Redirects and Forwards Cheat Sheet.