code: def count(self, signature = None):
          
          query = self._session.query(CrashDTO.id)
          if signature:
              sig_pickled = pickle.dumps(signature, protocol = 0)
              query = query.filter_by(signature = sig_pickled)
          return query.count()
docs: Counts how many crash dumps have been stored in this database.
          Optionally filters the count by heuristic signature.
  
          @type  signature: object
          @param signature: (Optional) Count only the crashes that match
              this signature. See L{Crash.signature} for more details.
  
          @rtype:  int
          @return: Count of crash dumps stored in this database.