docs: def _get_field_mapping(self, schema):
          """Get mapping for single field schema.
  
          :param schema: field schema
          """
          if 'mapping' in schema:
              return schema['mapping']
          elif schema['type'] == 'dict' and 'schema' in schema:
              return self._get_mapping(schema['schema'])
          elif schema['type'] == 'list' and 'schema' in schema.get('schema', {}):
              return self._get_mapping(schema['schema']['schema'])
          elif schema['type'] == 'datetime':
              return {'type': 'date'}
          elif schema['type'] == 'string' and schema.get('unique'):
              return {'type': 'string', 'index': 'not_analyzed'}