Created attachment 935965 [details]
there would be errors when deleting the category with cases belonging to.

Description of problem:
as summary.

Version-Release number of selected component (if applicable):
v3.8.10-2 on qa server.

How reproducible:
100%

Steps to Reproduce:
1.login the tcms as a superuser.
2.then add one new category belonging to a product. Check whether this category can be deleted.
3.then create a new case with the new category.Then check whether this category can be deleted.

Actual results:
if the category has no cases ,we can delete it.
else,it would have databases error.

Expected results:


Additional info:
the priority also has the same problem.