Django ORM manager for (naive) bulk upserting

db.py

from django.db import models


class BulkUpsertManager(models.Manager):
    @staticmethod
    def __filter_field(field):
        return not field.many_to_many

    @staticmethod
    def __to_serialized(field):
        if isinstance(field, datetime):
            return f"'{str(datetime)}'"

        if isinstance(field, bool):
            return str(1 if field else 0)

        if isinstance(field, int):
            return str(field)

        return f"{field}"

    @staticmethod
    def __to_value_tuple_list(value, all_fields):
        return [BulkUpsertManager.__to_serialized(getattr(value, v.name)) for v in all_fields if
                BulkUpsertManager.__filter_field(v)]

    def bulk_upsert(self, values, update_on_conflict=None):
        if not update_on_conflict:
            return []

        table_name = self.model._meta.db_table
        model_fields = self.model._meta.get_fields()

        # XXX: This is not how we should handle conflicting keys.
        pk_field = [f.name for f in model_fields if f.primary_key]
        all_fields = [f.name for f in model_fields if BulkUpsertManager.__filter_field(f)]
        set_fields = [f"{f}=EXCLUDED.{f}" for f in update_on_conflict]
        values_template = f"({', '.join(['%s'] * len(all_fields))})"

        sql_query = f"""
        INSERT INTO {table_name} ({', '.join(all_fields)})
        VALUES {', '.join([values_template] * len(values))}
        ON CONFLICT ({', '.join(pk_field)}) DO UPDATE SET {', '.join(set_fields)}
        """

        from django.db import connection
        with connection.cursor() as cursor:
            flatten = lambda l: [item for sublist in l for item in sublist]
            params = [BulkUpsertManager.__to_value_tuple_list(m, model_fields) for m in values]
            cursor.execute(sql_query, flatten(params))
            return cursor.rowcount