Django Querying chained Foreign Key

Question

Hello I am learning Django ORM queries and come to figure out reverse relationship in Foreign Key. I cannot visualize _set in foreign key field hope I will be cleared here. Here are my model I have been working.

class Location(BaseModel):
    name = models.CharField(
        max_length=50,
        validators=[validate_location_name],
        unique=True,
    )

I have Route model linked with Location as FK:

class Route(BaseModel):
    departure = models.ForeignKey(
        Location,
        on_delete=models.PROTECT,
        related_name='route_departure'
    )
    destination = models.ForeignKey(
        Location,
        on_delete=models.PROTECT,
        related_name='route_destination'
    )

Similarly I have Bus Company Route linked Foreign key with Route

class BusCompanyRoute(BaseModel):
    route = models.ForeignKey(Route, on_delete=models.PROTECT)

Finally I have Schedule Model linked with BusCompanyRoute as Fk

class Schedule(BaseModel):
    bus_company_route = models.ForeignKey(BusCompanyRoute, on_delete=models.PROTECT)

Problem is I want to query from views being on Schedule model want to link with departure and destination how will I do that? I have only done this so far on view.py

schedule = Schedule.objects.all()

I am stuck on querying Chained foreign key

What exactly you are trying to get, it is unclear can you elaborate with example — iklinac, Jan 07 '21 at 02:55
I want to query `departure ` and `destination` from `Schedule` — lord stock, Jan 07 '21 at 03:09

ruddra · Accepted Answer · 2021-01-07T06:20:01.810

2

You can simply try like this:

Schedule.objects.filter(bus_company_route__route__departure__name="A", bus_company_route__route__destination__name="B")

For more information, please see how you can follow lookup in Django.

edited Jan 07 '21 at 06:20

answered Jan 07 '21 at 05:41

ruddra

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one query: all foreign key above were one to many so that is reason we applied `bus_company_route__route__departure__name ='A'` ? PS: can you help me linking documentation for this concept. – lord stock Jan 07 '21 at 06:07
1

Sure. Documentation link: https://docs.djangoproject.com/en/3.1/topics/db/queries/#lookups-that-span-relationships – ruddra Jan 07 '21 at 06:19

score 1 · Answer 2 · answered Jan 07 '21 at 05:39

I am continuing from your code, as everything looks fine

schedule = Schedule.objects.all()

for s in schedule:
    current_schedule_route = s.bus_company_route.route
    departure = current_schedule_route.destination.name
    destination = current_schedule_route.destination.name
    print(departure, '->', destination)

you don't need reverse relation to query departure and destination from Schedule

an easy explaination of reverse relation along with its use case can be found here

Django Querying chained Foreign Key

2 Answers2