addPostFilterAggregation example

        $groupings = $criteria->getGroupFields();

        if (\count($groupings) === 1) {
            $first = array_shift($groupings);

            $accessor = $this->criteriaParser->buildAccessor($definition, $first->getField(), $context);

            $aggregation = new CardinalityAggregation('total-count');
            $aggregation->setField($accessor);

            return $this->addPostFilterAggregation($criteria, $definition, $context, $aggregation);
        }

        $fields = [];
        foreach ($groupings as $grouping) {
            $accessor = $this->criteriaParser->buildAccessor($definition, $grouping->getField(), $context);

            $fields[] = sprintf(
                ' if (doc[\'%s\'].size()==0) { value = value + \'empty\'; } else { value = value + doc[\'%s\'].value; }',