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