class_docstr: Wrap MongoDB with three primary methods `read`, `write`, `remove`.
  
  Attributes
  ----------
  host : str
     Hostname or MongoDB compliant full credentials+address+database
     specification.
  
  Information on MongoDB `connection string
  <https://docs.mongodb.com/manual/reference/connection-string/>`_.
  
  .. seealso:: :class:`orion.core.io.database.Database` for more on attributes.
docstr: Convert index keys to MongoDB ones.
docstr_tok: ["Convert","index","keys","to","MongoDB","ones","."]
code: def _convert_index_keys(self, keys):
      """Convert index keys to MongoDB ones."""
      if not isinstance(keys, (list, tuple)):
          keys = [(keys, self.ASCENDING)]
  
      converted_keys = []
      for key, sort_order in keys:
          converted_keys.append(
              (key, self._convert_sort_order(sort_order))
          )
  
      return converted_keys
  
imports: import functools
  import pymongo
  from orion.core.io.database import Database, DatabaseError, DatabaseTimeout, DuplicateKeyError
label_desc: Use image node_id 11 for calling the MongoDB obj's underlying member method code with example usage: obj._convert_index_keys(keys) and returns: converted_keys