ClickHouse/src/Storages/MergeTree/MergedColumnOnlyOutputStream.h

#pragma once

#include <Storages/MergeTree/IMergedBlockOutputStream.h>

namespace DB
{

class MergeTreeDataPartWriterWide;

/// Writes only those columns that are in `header`
class MergedColumnOnlyOutputStream final : public IMergedBlockOutputStream
{
public:
    /// Pass empty 'already_written_offset_columns' first time then and pass the same object to subsequent instances of MergedColumnOnlyOutputStream
    ///  if you want to serialize elements of Nested data structure in different instances of MergedColumnOnlyOutputStream.
    MergedColumnOnlyOutputStream(
        const MergeTreeDataPartPtr & data_part,
        const StorageMetadataPtr & metadata_snapshot_,
        const Block & header_,
        CompressionCodecPtr default_codec_,
        const MergeTreeIndices & indices_to_recalc_,
        WrittenOffsetColumns * offset_columns_ = nullptr,
        const MergeTreeIndexGranularity & index_granularity = {},
        const MergeTreeIndexGranularityInfo * index_granularity_info_ = nullptr);

    Block getHeader() const override { return header; }
    void write(const Block & block) override;
    void writeSuffix() override;
    MergeTreeData::DataPart::Checksums
    writeSuffixAndGetChecksums(MergeTreeData::MutableDataPartPtr & new_part, MergeTreeData::DataPart::Checksums & all_checksums, bool sync = false);

private:
    Block header;
};

using MergedColumnOnlyOutputStreamPtr = std::shared_ptr<MergedColumnOnlyOutputStream>;


}