Django ORM: Reverse relation query multiple model from single models - django

Question

I am in trouble querying reverse relation, I learned a lot about select_related and prefetch_related, yet I failed to achieve this.
At first see my models:
from django.db import models
import uuid
class Person(models.Model):
alias = models.UUIDField(primary_key=True,default=uuid.uuid4, editable=False, unique=True)
name = models.CharField(max_length=20)
class Appointment(models.Model):
patient = models.ForeignKey(Person, related_name="patient_for_appointment", on_delete=models.CASCADE)
data = models.CharField(max_length=20)
class Sales(models.Model):
customer = models.ForeignKey(Person, related_name="customer_for_sales", on_delete=models.CASCADE)
amount = models.FloatField()
class Prescription(models.Model):
patient = models.ForeignKey(Person, related_name="Patient_for_prescription", on_delete=models.CASCADE)
details = models.CharField(max_length=100)
I am trying to filter Person Model to check if the person has any prescription, sales, and appointment I want to get these all with single query like the person. will filter it with a person alias (primary key)
I can filter it with separate query like
patient_alias = '53fsdfsdf-fdsfds-df-fdf'
queryset = Appointment.objects.filter(
patient__alias=patient_alias
)
But I don't want this, coz, it has a performance issue. I don't want this with separate query.
I want to query only Person model to check if a person has Appointment, prescription or Sales
like Person.objects.filter(alias='a person alias)
Can anyone please help me to achieve this?
Much appreciated

Answer 1

We can select all Persons, except the ones that hav no Appointment, nor a Sales or Prescription with:
Person.objects.exclude(
patient_for_appointment=None,
customer_for_sales=None,
Patient_for_prescription=None
)
This will yield a query that looks like:
SELECT person.alias, person.name
FROM person
WHERE NOT (
person.alias IN (
SELECT U0.alias
FROM person U0
LEFT OUTER JOIN prescription U1 ON U0.alias = U1.patient_id
WHERE U1.id IS NULL
)
AND person.alias IN (
SELECT U0.alias
FROM person U0
LEFT OUTER JOIN sales U1 ON U0.alias = U1.customer_id
WHERE U1.id IS NULL AND U0.alias = person.alias
)
AND person.alias IN (
SELECT U0.alias
FROM person U0
LEFT OUTER JOIN appointment U1
ON U0.alias = U1.patient_id
WHERE U1.id IS NULL AND U0.alias = person.alias
)
)
Or we can make a union, like:
Person.objects.filter(
patient_for_appointment__isnull=False
).union(
Person.objects.filter(customer_for_sales__isnull=False),
Person.objects.filter(Patient_for_prescription__isnull=False)
)
This will result in a query that looks like:
(
SELECT person.alias, person.name
FROM person
INNER JOIN appointment ON person.alias = appointment.patient_id
WHERE appointment.id IS NOT NULL
) UNION (
SELECT person.alias, person.name FROM person
INNER JOIN sales ON person.alias = sales.customer_id
WHERE sales.id IS NOT NULL
) UNION (
SELECT person.alias, person.name
FROM person
INNER JOIN prescription ON person.alias = prescription.patient_id
WHERE prescription.id IS NOT NULL
)