[FIX] util/records: fix delete_unused DOCSTRING

[Pirols]

delete_unused, in spite of its name, deletes records even if they are used, provided they are not part of a foreign key with restrict ondelete clause.

[robodoo]

[Pirols]

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[UemuS]

We could also mention that it does not handle indirect references.
If table 1 is referenced with ON DELETE CASCADE by table 2 and table 2 is restricted by table 3, the upgrade would crash.
I'm trying to fix this in addition to some other cases, but it's a bit tricky

[diagnoza]

I thought that it's somewhat implied that if there's no direct link in the database, the record won't be removed :p The term "used" is used in the sense that there is a constraint linking one record to another.

Imho what would be more important to mention is what Yazid said.

[Pirols]

We could also mention that it does not handle indirect references. If table 1 is referenced with ON DELETE CASCADE by table 2 and table 2 is restricted by table 3, the upgrade would crash.

That's a good idea, I will add a warning.

So the set null is the same as restrict, only cascade is ignored when checking fk on other tables.

This is right and I will clarify it in the DOCSTRING.

However, I think we should consider addressing this: the behavior sounds to be inconsistent when we have a set clause vs a restrict one on a direct/indirect reference. See the possibilities:

• Direct restrict reference -> no removal ✅
• Direct set reference -> no removal ✅
• Indirect restrict reference -> failure. Not ideal but at least it raises a concern ⚠️
• Indirect set reference -> (my untested guess) removes the records (and triggers the indirect ondelete clause). Inconsistent case ❌

But well if @UemuS manages to solve the indirect issue, this inconsistency will also be gone, just wanted to acknowledge it.

I thought that it's somewhat implied that if there's no direct link in the database, the record won't be removed :p

Exactly! And that's the problem with the name/DOCSTRING: they don't explain that records will still be removed if their references can cascade.

[Pirols]

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