def alter_field(self, model, old_field, new_field, strict=False):
        """Ran when the configuration on a field changed."""

        is_old_field_hstore = isinstance(old_field, HStoreField)
        is_new_field_hstore = isinstance(new_field, HStoreField)

        if not is_old_field_hstore and not is_new_field_hstore:
            return

        old_uniqueness = getattr(old_field, 'uniqueness', []) or []
        new_uniqueness = getattr(new_field, 'uniqueness', []) or []

        # handle field renames before moving on
        if str(old_field.column) != str(new_field.column):
            for keys in self._iterate_uniqueness_keys(old_field):
                self._rename_hstore_unique(
                    model._meta.db_table,
                    model._meta.db_table,
                    old_field,
                    new_field,
                    keys
                )

        # drop the indexes for keys that have been removed
        for keys in old_uniqueness:
            if keys not in new_uniqueness:
                self._drop_hstore_unique(
                    model,
                    old_field,
                    self._compose_keys(keys)
                )

        # create new indexes for keys that have been added
        for keys in new_uniqueness:
            if keys not in old_uniqueness:
                self._create_hstore_unique(
                    model,
                    new_field,
                    self._compose_keys(keys)
                )
Ran when the configuration on a field changed.