Method _from_son

mongoengine/base/document.py:779–846

Create an instance of a Document (subclass) from a PyMongo SON (dict)

(cls, son, _auto_dereference=True, created=False)

    @classmethod
    def _from_son(cls, son, _auto_dereference=True, created=False):
        """Create an instance of a Document (subclass) from a PyMongo SON (dict)"""
        if son and not isinstance(son, dict):
            raise ValueError(
                "The source SON object needs to be of type 'dict' but a '%s' was found"
                % type(son)
            )

        # Get the class name from the document, falling back to the given
        # class if unavailable
        class_name = son.get("_cls", cls._class_name)

        # Convert SON to a data dict, making sure each key is a string and
        # corresponds to the right db field.
        # This is needed as _from_son is currently called both from BaseDocument.__init__
        # and from EmbeddedDocumentField.to_python
        data = {}
        for key, value in son.items():
            key = str(key)
            key = cls._db_field_map.get(key, key)
            data[key] = value

        # Return correct subclass for document type
        if class_name != cls._class_name:
            cls = get_document(class_name)

        errors_dict = {}

        fields = cls._fields
        if not _auto_dereference:
            # if auto_deref is turned off, we copy the fields so
            # we can mutate the auto_dereference of the fields
            fields = copy.deepcopy(fields)

        # Apply field-name / db-field conversion
        for field_name, field in fields.items():
            field.set_auto_dereferencing(
                _auto_dereference
            )  # align the field's auto-dereferencing with the document's
            if field.db_field in data:
                value = data[field.db_field]
                try:
                    data[field_name] = (
                        value if value is None else field.to_python(value)
                    )
                    if field_name != field.db_field:
                        del data[field.db_field]
                except (AttributeError, ValueError) as e:
                    errors_dict[field_name] = e

        if errors_dict:
            errors = "\n".join([f"Field '{k}' - {v}" for k, v in errors_dict.items()])
            msg = "Invalid data to create a `{}` instance.\n{}".format(
                cls._class_name,
                errors,
            )
            raise InvalidDocumentError(msg)