CODEWITHSUNDEEP
pythonmysqldjango
David542
David542

Reputation: 110452

How to prevent foreign key lookup in django

I am trying to do the following query:

SELECT * FROM catalog WHERE master_id IS NULL

The master field is a ForeignKey, but in this case, I just need to know whether it is NULL or not so I don't need to do a foreign key lookup. However, if I do:

Catalog.objects.filter(master_id=None).values_list('is_tv', flat=True).count()

Here is the example statement it does:

SELECT ••• FROM `catalog` LEFT OUTER JOIN `main_titlemaster` 
    ON (`main_catalog`.`master_id` = `main_titlemaster`.`id`) 
    WHERE `main_titlemaster`.`id` IS NULL

How can I prevent this useless FK lookup without diving into raw SQL?

Upvotes: 1

Views: 90

Answers (1)

Ozgur Vatansever
Ozgur Vatansever

Reputation: 52203

You should use __isnull lookup keyword.

Catalog.objects.filter(master__isnull=True).values_list('is_tv', flat=True).count()

Upvotes: 3

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