builder.setSize(size);
        }

        // set query.
        final QueryBuilder q = buildQuery(query, fields);

        // set function score
        final QueryBuilder queryBuilder = buildFunctionScoreQuery(query, q);
        builder.addSort("_score", SortOrder.DESC);

        // set filter query.
        final List<QueryBuilder> filterList = new ArrayList<>(10);
        if (!tags.isEmpty()) {