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88 lines
2.0 KiB
C++
88 lines
2.0 KiB
C++
#pragma once
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#include <cstring>
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#include <cassert>
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#include <Columns/IColumn.h>
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#include <Common/PODArray.h>
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#include <Columns/ColumnString.h>
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#include <Columns/ColumnFixedString.h>
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#include <IO/WriteBufferFromVector.h>
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namespace DB
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{
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namespace ErrorCodes
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{
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extern const int TOO_LARGE_STRING_SIZE;
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}
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namespace ColumnStringHelpers
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{
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/** Simplifies writing data to the ColumnString or ColumnFixedString via WriteBuffer.
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*
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* Take care of little subtle details, like padding or proper offsets.
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*/
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template <typename ColumnType>
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class WriteHelper
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{
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ColumnType & col;
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WriteBufferFromVector<typename ColumnType::Chars> buffer;
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size_t prev_row_buffer_size = 0;
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public:
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WriteHelper(ColumnType & col_, size_t expected_rows)
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: col(col_)
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, buffer(col.getChars())
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{
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if constexpr (std::is_same_v<ColumnType, ColumnFixedString>)
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col.reserve(expected_rows);
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else
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{
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col.getOffsets().reserve(expected_rows);
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/// Using coefficient 2 for initial size is arbitrary.
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col.getChars().resize(expected_rows * 2);
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}
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}
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~WriteHelper() = default;
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void finalize()
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{
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buffer.finalize();
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}
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auto & getWriteBuffer()
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{
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return buffer;
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}
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inline void rowWritten()
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{
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if constexpr (std::is_same_v<ColumnType, ColumnFixedString>)
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{
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if (buffer.count() > prev_row_buffer_size + col.getN())
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throw Exception(
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ErrorCodes::TOO_LARGE_STRING_SIZE,
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"Too large string for FixedString column");
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// Pad with zeroes on the right to maintain FixedString invariant.
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const auto excess_bytes = buffer.count() % col.getN();
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const auto fill_bytes = col.getN() - excess_bytes;
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writeChar(0, fill_bytes, buffer);
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}
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else
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{
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writeChar(0, buffer);
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col.getOffsets().push_back(buffer.count());
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}
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prev_row_buffer_size = buffer.count();
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}
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};
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}
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}
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