Return a json dictionary representing this model.

def _to_dict(self):
        """Return a json dictionary representing this model."""
        _dict = {}
        if hasattr(self, 'entity') and self.entity is not None:
            _dict['entity'] = self.entity
        if hasattr(self, 'description') and self.description is not None:
            _dict['description'] = self.description
        if hasattr(self, 'metadata') and self.metadata is not None:
            _dict['metadata'] = self.metadata
        if hasattr(self, 'fuzzy_match') and self.fuzzy_match is not None:
            _dict['fuzzy_match'] = self.fuzzy_match
        if hasattr(self, 'created') and self.created is not None:
            _dict['created'] = datetime_to_string(self.created)
        if hasattr(self, 'updated') and self.updated is not None:
            _dict['updated'] = datetime_to_string(self.updated)
        if hasattr(self, 'values') and self.values is not None:
            _dict['values'] = [x._to_dict() for x in self.values]
        return _dict