SafeQuery
Safely query stuff in ActiveRecord.
Why
To prevent unbounded resource consumption, we always want to limit how many rows can be returned from database fetches.
Calls to ActiveRecord::Relation#each
(without a LIMIT clause) are dangerous and should be avoided, because they can accidentally trigger an
unpaginated database fetch for millions of rows, which can exhaust your web server or database resources. Exceptions to this rule should be carefully vetted.
Worse, it's common to hit this problem only in production, because development environments seldom contain enough database rows to highlight the issue. This makes it easy to write code that seems to work well, but fails when operating on a database with more data.
This gem raises an exception whenever you attempt to call ActiveRecord::Relation#each
, giving you the opportunity to catch and fix
this before any unsafe code hits production.
How it works
With this gem installed, Rails will throw an exception when you make an unsafe query.
Compatibility:
- Rails 5+
- Ruby 2.6+
- Postgres, MySQL, SQLite, maybe others (untested)
Installation:
Add to your gemfile:
gem 'safe_query', group: [:development, :test]
then bundle install
.
It's recommended to set config.active_record.warn_on_records_fetched_greater_than
(available since Rails 5), so you have warnings
whenever a query is returning more rows than expected, even when using this gem.
For example, if your app is never supposed to have no more than 100 records per page, add to config/environments/development.rb
:
config.active_record.warn_on_records_fetched_greater_than = 100
Example fixes:
Use find_each
instead
Sometimes the fix is as easy as changing
book.authors.each do |author|
to this:
book.authors.find_each do |author|
Sometimes this doesn't work:
- For some reason you don't have an autoincrementing primary key ID for Rails to paginate on
- You have a specific sort order and you want to maintain the sort order
In those cases, you may have to add some custom code to maintain your existing app behavior. But otherwise, you can
use find_each
or any other solution from the ActiveRecord::Batches API.
Paginate your results
Use your existing pagination solution, or look at adding pagy, kaminari, will_paginate, etc to your app.
Just add a limit
clause
Sometimes you are simply missing a limit clause in your query. This might be the case if you have an implied upper bound on the number of results enforced by the application elsewhere. SafeQuery will find cases where this limit isn't expressed in your queries, which might be a problem if your enforcement logic is flawed in some way.
Ignore this problem
You can ignore this problem by converting the relation to an array with to_a
before you operate on it:
book..find_by ...
to this:
book..to_a.find_by ...