How to select related plus one?

Hi,

I have two models A and B:

 

class A(models.Model):
   some_fields

   number
   category

class B(models.Model):
   models.ForeignKey(A)

   some_fields

I need to select all records from A  which are present in B and the next number in A in the same category.

 

for example data in A (first column is id):
( 1, some_fields, 1, 2)
( 2, some_fields, 3, 3)

( 3, some_fields, 2, 2)

( 4, some_fields, 3, 2)

( 5, some_fields, 4, 2)

data in B:

( 1, 1)

( 2, 3)

so the queryset should return a 1,3,4 records from A.

I'm completely lost and have no idea how to do that.

I tried to implement that thing via django.db.models.F , but without success.

Could somebody please give me an advice how to implement that?

 

--

wbr,

rush.

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