在Django Orm中使用In语句

Question

I have 3 tables say

Table1       Table2                   Category
======       =================        ==============
id, name     id, Table1_id, name      category_id, Table2_id, name

Now given a category_id, I have to find those names in Table1 that belongs to that category_id

The only solution that I can think of right know is to make 2 queries like this

similar_ids = Table2.objects.filter(category__category_id=_cat_id).values_list('id')

similar_names = Table1.objects.filter(table2__id__in=similar_ids).values_list('name').distinct()

Is their a way to do it in a single query.

Also given the size of the 3 tables (Table1 == 30,000 rows, Table2 and Category == 125000 rows) what will be the right thing to do :-

1. Make a single query by joining all the tables at once
2. breaking it into 2 parts (as above)

Answer 1

The way you represented your models is quite obscure from a django standpoint. That is, it's hard to use correct related_name s in this case. But let's try. You would want:

Table1.objects.filter(table2_set__category_set__id=myid).values_list('name')

Answer 2

Django will not generate two queries for your original query. If you do table2__id__in=similar_ids, Django will automatically use a subquery.