`Query.has_results` calls `.exists()` with wrong argument

[Flavio Curella]

The has_results method of the Query class (in django/db/models/sql/query.py), passes the using argument to the exists() method:

    def has_results(self, using):
        q = self.exists(using)
        compiler = q.get_compiler(using=using)
        return compiler.has_results()

but the signature of the exists method does not accept an argument to select the db connection. It only accepts an argument to limit the rows it should fetch:

    def exists(self, limit=True):
        # ... snip ...

[Simon Charette]

Regression caused by 3d734c09ff0138441dfe0a59010435871d17950f, I really wish we had type checking in this part of the code base to catch these kind of bugs that flew under the radar for almost two years.

[Mariusz Felisiak]

Replying to Simon Charette:

Regression caused by 3d734c09ff0138441dfe0a59010435871d17950f, I really wish we had type checking in this part of the code base to catch these kind of bugs that flew under the radar for almost two years.

Unfortunately, it hasn't change the behavior, because limit is True by default and we check if it's truthy in Query.exists().

[Flavio Curella]

should I change to check to if limit is True:?

[Mariusz Felisiak]

Replying to Flavio Curella:

should I change to check to if limit is True:?

Sounds good +1.

[Flavio Curella]

Done.

[Mariusz Felisiak]

​PR

[Natalia Bidart]

PR looks good but it needs a regression test.

[Mariusz Felisiak]

Replying to Natalia Bidart:

PR looks good but it needs a regression test.

IMO, it's not worth adding a regression test when the only doable option is to mock exists() call in has_results() and assert passed arguments.

[Tim Graham]

I agree with Mariusz. Testing implementation details like this seems more likely to add a maintenance burden in future refactors than to add any value. As far as I can tell, this mistake didn't cause an actual problem.

[GitHub <noreply@…>]

In f9bf616:

Fixed #35585 -- Corrected Query.exists() call in Query.has_results().