[Answer]-Django ORM join with another table

by

1đź‘Ť

âś…

It sounds like you have a “polymorphic association”. There are a couple ways to do analogous things in Django, but I think the one that most closely matches what you described is the contenttypes module, which uses separate columns for the type and for the value as in your application.

👤Andrew Gorcester

0đź‘Ť

You may just want to define a multi-table inheritance structure. This gets you the same result in that you have multiple types of messages and field inheritance, but you don’t have to mess with a type field at all. 

class Message(models.Model):
    value = models.CharField(max_length=9000)

class Event(Message):
    pass

class Tweet(Message):
    pass

In view post handler:

...
if request.POST['type'] == 'event':
    Event.objects.create(value=request.POST['value'])
elif request.POST['type'] == 'tweet':
    Tweet.objects.create(value=request.POST['value'])
...

Then, get your objects:

all_tweets = Tweet.objects.all()
all_messages = Message.objects.all()

for message in all_messages:
    try:
        event = message.event
    except Event.DoesNotExist:
        # this message is not an Event
        pass

If this sort of structure doesn’t work for you, there are two other styles of Model inheritance supported by Django: Abstract base classes and Proxy models. You could also hold a GenericForeignKey as suggested by @AndrewGorcester.

👤dokkaebi

Leave a comment