base_column.hpp

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#pragma once
 
/// @file userver/storages/clickhouse/io/columns/base_column.hpp
/// @brief @copybrief storages::clickhouse::io::columns::ClickhouseColumn
 
#include <userver/storages/clickhouse/io/columns/column_iterator.hpp>
#include <userver/storages/clickhouse/io/columns/column_wrapper.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace storages::clickhouse::io::columns {
 
// clang-format off
/// @brief Base class for every typed ClickHouse column.
/// To add new columns one should derive from this class,
/// define types aliases:
/// - `cpp_type` - to what C++ types are column values mapped,
/// - `container_type` (being `std::vector<cpp_type>`)
///
/// and implement 3 methods:
/// - `ctor(ColumnRef)` - column constructor,
/// - `static ColumnRef Serialize(const container_type&)` - constructs a column from C++ container,
/// - `cpp_type ColumnIterator<YourColumnType>::DataHolder::Get()`
///
/// see implementation of any of the existing columns for better understanding.
// clang-format on
template <typename ColumnType>
class ClickhouseColumn {
public:
    using iterator = ColumnIterator<ColumnType>;
 
    ClickhouseColumn(ColumnRef column) : column_{std::move(column)} {}
 
    iterator begin() const { return iterator{column_}; }
 
    iterator end() const { return iterator::End(column_); }
 
    size_t Size() const { return GetColumnSize(column_); }
 
private:
    ColumnRef column_;
};
class ClickhouseColumn {…};
 
}  // namespace storages::clickhouse::io::columns
 
USERVER_NAMESPACE_END