Fixed circular import in nft_util

db/db.py

@@ -75,6 +75,8 @@ class DB(metaclass=Singleton):
         self._session.commit()
 
     def add_candidate(self, candidate: Candidate):
+        if self._session.query(Candidate).filter(Candidate.id == candidate.id).first() is not None:
+            return
         tres = TestResult(answers=[])
         candidate.test_result = [tres]
         self._session.add(candidate)