Using related models with conditional expression - python-3.x

Question

Goal: use a related model attribute as a filter inside a conditional expression for an annotation.
I'm currently adding some functionality to an old Django app, this app has some design issues and i have nothing to do with it. After some research I found conditional expressions, this is great and what I needed.
However I'm not being able to make it.
Let's have model A, model B and model C.
class ModelA(models.Model):
name=models.Charfield()
reference=models.ForeignKey('app.ModelB')
class ModelB(models.Model):
name=models.Charfield()
class ModelC(models.Model):
name=models.Charfield()
reference=models.ForeignKey('app.ModelB', related_name='some_reference')
bool_field=models.BooleanField()
And this is what I would like to do:
ModelA.objects.all().annotate(some_field=When(Q(reference__some_reference__bool_field=True),
then=F('reference_some_reference_name')))
This should work since it is being interpreted by python, but I get some Syntax Error from MySQL.
What am i doing wrong? Is this even possible?
This is what I'm getting:
django.db.utils.ProgrammingError: (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'WHEN `ParametrosPreciosProveedor`.`already_iva` = 1 THEN `ParametrosPreciosProve' at line 1")
'ParametrosPreciosProveedor' is ModelC in this example and 'already_iva' is bool_field.

Answer 1

I would try removing the When and then parts of the annotation. Q objects do those automatically - you don't define those terms in Python.
ModelA.objects.all().annotate(some_field=Q(reference__some_reference__bool_field=True),
F('reference_some_reference_name')))
Check out the docs to see how to use Q()