django prefetch_related和select_related在父表上

Question

I have the following db structure:

catogory
   id
   name
   parent_id

class Category(models.Model)
  name = models.CharField(max_length=400, blank=True, null=True)
  parent = models.ForeignKey("self", blank=True, null=True)

I need to fetch all categories and their parent.

If I do:

Category.objects.select_related("parent").filter(pk__in=[ids])

it would just return the parent of the first level.

How can I retrieve the parents of all level with minimum db calls?

My approach is to build a new non-db-model objects eg: CategorySerializer that will transfer those Category models to non db ones so the logic layer could use it

Answer 1

What if you created a function that you can call recursively until there are no more parents left

def get_categories(ids):
    ids = list(Category.objects.select_related("parent").filter(pk__in=[ids]).values_list('parent_id', flat=True))
    if len(ids) == 0:
        return []
    else:
        return ids + get_categories(ids)

So start with this call

all_parent_ids = []
for category in list(Category.objects.all()):
    all_parent_ids.append(get_categories(category.parent_id))

I haven't tested this, so it may need some refinement, but I believe the idea is correct.