private void traverseByLabel()

in hugegraph-core/src/main/java/org/apache/hugegraph/backend/tx/GraphTransaction.java [2039:2109]
57 lines of code
12 McCabe index (conditional complexity)

    private <T> void traverseByLabel(SchemaLabel label,
                                     Function<Query, Iterator<T>> fetcher,
                                     Consumer<T> consumer, boolean deleting) {
        HugeType type = label.type() == HugeType.VERTEX_LABEL ?
                        HugeType.VERTEX : HugeType.EDGE;
        Query query = label.enableLabelIndex() ? new ConditionQuery(type) :
                                                 new Query(type);
        query.capacity(Query.NO_CAPACITY);
        query.limit(Query.NO_LIMIT);
        if (this.store().features().supportsQueryByPage()) {
            query.page(PageInfo.PAGE_NONE);
        }
        if (label.hidden()) {
            query.showHidden(true);
        }
        query.showDeleting(deleting);
        query.showExpired(deleting);

        if (label.enableLabelIndex()) {
            // Support label index, query by label index by paging
            assert query instanceof ConditionQuery;
            ((ConditionQuery) query).eq(HugeKeys.LABEL, label.id());
            Iterator<T> iter = fetcher.apply(query);
            try {
                // Fetch by paging automatically
                while (iter.hasNext()) {
                    consumer.accept(iter.next());
                    /*
                     * Commit per batch to avoid too much data in single commit,
                     * especially for Cassandra backend
                     */
                    this.commitIfGtSize(GraphTransaction.COMMIT_BATCH);
                }
                // Commit changes if exists
                this.commit();
            } finally {
                CloseableIterator.closeIterator(iter);
            }
        } else {
            // Not support label index, query all and filter by label
            if (query.paging()) {
                query.limit(this.pageSize);
            }
            String page = null;
            do {
                Iterator<T> iter = fetcher.apply(query);
                try {
                    while (iter.hasNext()) {
                        T e = iter.next();
                        SchemaLabel elemLabel = ((HugeElement) e).schemaLabel();
                        if (label.equals(elemLabel)) {
                            consumer.accept(e);
                            /*
                             * Commit per batch to avoid too much data in single
                             * commit, especially for Cassandra backend
                             */
                            this.commitIfGtSize(GraphTransaction.COMMIT_BATCH);
                        }
                    }
                    // Commit changes of every page before next page query
                    this.commit();
                    if (query.paging()) {
                        page = PageInfo.pageState(iter).toString();
                        query.page(page);
                    }
                } finally {
                    CloseableIterator.closeIterator(iter);
                }
            } while (page != null);
        }
    }