code: def from_config(config_file, use_admin=False):
          
          with open(config_file) as f:
              d = json.load(f)
              user = d["admin_user"] if use_admin else d["readonly_user"]
              password = d["admin_password"] if use_admin \
                  else d["readonly_password"]
              return QueryEngine(
                  host=d["host"], port=d["port"], database=d["database"],
                  user=user, password=password, collection=d["collection"],
                  aliases_config=d.get("aliases_config", None))
docs: Initialize a QueryEngine from a JSON config file generated using mgdb
          init.
  
          Args:
              config_file:
                  Filename of config file.
              use_admin:
                  If True, the admin user and password in the config file is
                  used. Otherwise, the readonly_user and password is used.
                  Defaults to False.
  
          Returns:
              QueryEngine