如果对obj有FK依赖关系，请不要删除

Question

I want to do a DELETE operation for an item in django, but only if there are no FK dependencies. I would normally do this:

Catalog.objects.filter(pk=pk).delete()

Which would delete the item and then delete/nullify any dependencies to this particular Catalog object. However, I do not want to delete the item if there are any dependencies. How would I do that in django? I was thinking -

list(Catalog objects.raw('DELETE FROM main_catalog WHERE pk=%s', pk))

Answer 1

You can use the exists() command in your query.

if main_catalog.objects.filter(catalog__id=pk).exists():
    pass
else:
    Catalog.objects.filter(pk=pk).delete()

Answer 2

First of all, use a get() with a foreign key, as you only expect one object to be returned. Then check for foreign keys on that object.

catalog = Catalog.objects.get(pk=pk)
if  catalog.foreign_key_1 or catalog.foreign_key_2 :  # repeat or's with all fk's on the object
    pass
else : 
    catalog.delete()