CODEWITHSUNDEEP
pythondjango
barciewicz
barciewicz

Reputation: 3773

Django database: how to filter objects based on other object's field?

In the code below, how do I filter capital_listings so to return listings only for capital cities? Also, is it possible to get rid of the intermediate capitals_names list?

capitals = City.objects.filter(status='capital')
capitals_names = [capital.name for capital in capitals]
capital_listings = Listing.objects.filter #???

Models:

class Listing(models.Model):
    city = models.CharField(max_length = 30, default = 'placeholder')
    date_added = models.DateTimeField()

    def __str__(self):
        return self.name

class City(models.Model):
    name = models.CharField(max_length = 30, default = 'placeholder')
    status = models.CharField(max_length = 30, default = 'placeholder')

    def __str__(self):
        return self.name

Upvotes: 1

Views: 230

Answers (2)

Håken Lid
Håken Lid

Reputation: 23064

If you change Listings.city to a foreignkey relationship, you can do your query in a single step.

class City(models.Model):
    name = models.CharField(max_length = 30, default = 'placeholder')
    status = models.CharField(max_length = 30, default = 'placeholder')

class Listing(models.Model):
    city = models.ForeignKey(City, on_delete=models.CASCADE)


capital_listings = Listing.objects.filter(city__status='capital')

This is explained in the docs:

https://docs.djangoproject.com/en/2.1/topics/db/queries/#lookups-that-span-relationships

Upvotes: 0

Gevorg Davoian
Gevorg Davoian

Reputation: 524

capital_listings = Listing.objects.filter(city__in=capital_names)

Upvotes: 2

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