How to execute aggregate function in prefetch_related?

Question

Django

Here are the models:

class ObjectDataAdditional(models.Model):
    percentage_technical_readiness = models.FloatField(
        null=True,
    )
    #какие-то поля


class ObjectDataNormalized(models.Model):
    #какие-то поля


class NormalizedAdditional(models.Model):
    normalized_object = models.ForeignKey(
        ObjectDataNormalized,
        on_delete=models.CASCADE,
        null=True,
        related_name='normal_object',
    )
    additional_object = models.ForeignKey(
        ObjectDataAdditional,
        on_delete=models.CASCADE,
        related_name='additional_object',
        null=True,
    )


class LinkedData(models.Model):
    many = models.ManyToManyField(
        ObjectDataNormalized,
        related_name='many_related',
    )


class LinkedInfo(models.Model):
    linked_data = models.ForeignKey(
        LinkedData,
        on_delete=models.CASCADE,
        related_name='linked_data_related'
    )
    normalized = models.ForeignKey(
        ObjectDataNormalized,
        on_delete=models.CASCADE,
        related_name='normalized_related'
    )
    main = models.BooleanField(
        default=False,
        null=False,
    )

One object ObjectDataNormalizedcan have several ObjectDataAdditional. All binding goes to NormalizedAdditional.
I need to get data from all listed tables. This is how I am trying to do it:

prefetch = Prefetch('normalized__normal_object',  queryset=NormalizedAdditional.objects.
annotate(max_percentage=Max('additional_object__percentage_technical_readiness')))

info = LinkedInfo.objects.all().order_by('linked_data_id',
                                                 '-main').select_related(
            'linked_data',
            'normalized',
        ).prefetch_related(prefetch)

Everything seems to be working. From infoI can pull out data from LinkedInfo, linked_data, normalizedbut I cannot get the value percentage_technical_readiness. A lot of how I tried to pull this value out actually.
That is, in a table NormalizedAdditional, one object normalized_objectcan have several ObjectDataAdditional:

normalized_object_id	additional_object_id
8	                                6580
8	                                6579
9	                                11006
9	                                10999

And I need to pull the maximum value percentage_technical_readinessfor the normalized_object. The field percentage_technical_readinessis in the table ObjectDataAdditional.
Or maybe Django ORM is not suitable for such complex queries? Can in such cases it is better to use stored procedures?

Answer 1

Try Prefetch(qs)