python-Django模型查询

Question

I've 2 models :

class A(models.Model):
    a_id = models.CharField(max_length = 255, primary_key = True)
    destination = models.CharField(max_length = 255)

class B(models.Model):
    a_id = models.ForeignKey('A', related_name = 'pptls')
    some_unique_value = models.CharField(max_length = 255, unique = True)

I want to get destination from A given the some_unique_value from B .

This is how I'm currently doing:-

a_id = B.objects.get(some_unique_value = "something").a_id
destination = A.objects.get(a_id = a_id).destination

Though, it fetches me the results, but I want to convert this into single line query, something like joins in SQL. How can I do it?

Answer 1

You use the double-underscore syntax to traverse relationships:

destination = A.objects.get(b__some_unique_value="something").destination

This is very well covered in the documentation on making queries .

(Also, please don't name your ForeignKeys "_id": it doesn't represent an ID, it represents an actual object of the other class. Django automatically appends "_id" to the underlying database field anyway.)