docs: def nr_cases(self, snv_cases=None, sv_cases=None):
          """Return the number of cases in the database
  
          Args:
              snv_cases(bool): If only snv cases should be searched
              sv_cases(bool): If only snv cases should be searched
  
          Returns:
              cases (Iterable(Case)): A iterable with mongo cases
          """
          query = {}
          
          if snv_cases:
              query = {'vcf_path': {'$exists':True}}
          if sv_cases:
              query = {'vcf_sv_path': {'$exists':True}}
          if snv_cases and sv_cases:
              query = None
  
          return self.db.case.count_documents(query)