I always thought of 1+N as a thing that you just keep in your head, catch on code reviews or via performance regressions. This worked well for a long time, however, the less control we have over our SQL queries the more likely it will sneak through those guards.
A small history dive
This used to be very visible and meant almost “do not perform SQL queries in a cycle”:
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With ORM and lazy loading this became a little bit less obvious:
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With something so innocent as an attribute access making an SQL query, it’s much easier to miss it. Especially when this code spreads out, the ORM objects are passed to templates, which also have loops and sure they can do attribute access.
As project grows, as its database schema becomes more complicated, as your team grows too, this keeps adding up. And magic also adds up. One particular mention should be a GraphQL library, which resolves onto ORM automatically.
Back to the present
I tumbled on a couple of 1+Ns while reading a project code for an unrelated reason and it got me thinking – do I ever want Django to do that lazy loading stuff? And the answer was never. This was a misfeature for me, the need for such thing is quite circumstantial, usually when you load a list of things you need the same data about all of them, so it doesn’t make sense to lazy load extra data for each object separately. Either eager load or batch lazy load, the latter Django does not do.
So, anyway, if I don’t need this than I might as well prohibit it, which turned out to be quite easy to do:
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This way 1+N will blow up instead. Great, we’ll catch it during tests. The thing is, however, if 1+Ns were passing our defences before they will probably continue now and this will explode in production. With this in mind, a flood guard and some explanations it transforms into:
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Which is ready to be used as is. Simply need to put or import it somewhere.
P.S. A small bonus – how I tried to make ChatGPT write this post for me. It was mostly failure :), but refactoring the code sample was done nicely.