How to execute custom SQL query when deleting a model item in Django?

Question

I want to execute an SQL query, when an item gets deleted in the admin interface. In models.py I do this:

from django.db import connection

class LList(models.Model):
    item = models.ForeignKey(Item, models.DO_NOTHING)

    def delete(self, *args, **kwargs):
        cursor = connection.cursor()
        cursor.execute('DELETE FROM some_table where item = %d', [self.item.id])

When I turn debugging on I see all the queries executed. It seems the DELETE FROM query is not executed, I only see

(0.000) DELETE FROM `llist` WHERE `llist`.`id` IN (27); args=(27,)

Why is the other DELETE FROM query not executed? How can I fix that?

How did you execute the delete operation in the admin interface? — JPG
– JPG, Commented Oct 9, 2019 at 6:04
Oh I see what you mean, didn't know there were 2 possibilities to delete an item. I want the SQL query beeing executed in both possible ways, with delete selected and delete. — defoe
– defoe, Commented Oct 9, 2019 at 15:27

HabibUllah Khan · Accepted Answer · 2019-10-09 10:51:02Z

2

You are overriding the delete function the wrong way,

def delete(self, using=None, keep_parents=False):
    with connection.cursor() as cursor:
        cursor.execute('''DELETE FROM some_table where item = %d''', [self.item.id])

    super(LList, self).delete(using, keep_parents)

But I believe the better way would be to do it using signals, you should create a pre_delete signal.

answered Oct 9, 2019 at 10:51

HabibUllah Khan

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2 Comments

defoe Over a year ago

Great, this way the direct delete works, but when I delete the item via delete selected it does not work. What kind of function do I have to call in this case?

HabibUllah Khan Over a year ago

Can you please write down the sql query that you are trying to execute. I will be better able to solve the problem then.

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