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Add ability to prevent access to a database

Rodrigo Muino Tomonari requested to merge github/fork/stevecrozz/while-preventing-access into main

Created by: stevecrozz

Motivation / Background

From discussion: https://discuss.rubyonrails.org/t/proposal-prevent-activerecord-access/85322

I have some methods that I know are being called in loops and these methods will become N+1 DB query situations if a database query is generated in any way. What I’m hoping for is some sort of runtime policy that says “no ActiveRecord access is allowed in here, you must load everything you need first”

Here’s another way to put it. If I have some business logic that combines data loading with some kind of pure calculation, it would be nice to have the power, when it is useful, to strongly separate these concerns and be sure the separation remains.

This power could be useful for any situation where a hot code path must remain free of queries. Perhaps it could be used to implement a policy to prevent database access during the render phase of an HTTP request.

N+1 queries can be a real performance concern. It isn't always immediately obvious what the impacts could be of adding a new query. I wish engineers would be constantly watching the query log as they work. But things can get out of hand quickly, and even if you are watching the wall of queries being logged, N+1s can sometimes disappear into the noise.

Also, there are times when I want a pure in-memory algorithm. An API like this would allow me to both express and enforce the intention to not be hitting the database in a branch of code.

Just today, I was working with some code that broke a test that asserts for a given controller action, exactly 118 queries are dispatched. This is a terrible test to have, but we have it because we have had real problems with query explosions emerging unexpectedly. I believe strict loading could help, but it would not have prevented all of the problems that led to write and maintain this test.

This is indeed a heavy hammer to use. But I don't see an alternative that can achieve the same level of assurance, and the implementation was pretty easy thanks to the prior art of while_preventing_writes.

Detail

This Pull Request adds while_preventing_access to the public API of ActiveRecord::Base much like was done for while_preventing_writes in https://github.com/rails/rails/pull/34505

Additional information

Checklist

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  • This Pull Request is related to one change. Unrelated changes should be opened in separate PRs.
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  • Tests are added or updated if you fix a bug or add a feature.
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