Filters given entity queryset by an attribute which is linked to given
        schema and has given value in the field for schema's datatype.

def _filter_by_simple_schema(self, qs, lookup, sublookup, value, schema):
        """
        Filters given entity queryset by an attribute which is linked to given
        schema and has given value in the field for schema's datatype.
        """
        value_lookup = 'attrs__value_%s' % schema.datatype
        if sublookup:
            value_lookup = '%s__%s' % (value_lookup, sublookup)
        return {
            'attrs__schema': schema,
            str(value_lookup): value
        }