execution_result.hpp

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#pragma once
 
/// @file userver/storages/clickhouse/execution_result.hpp
/// @brief Result accessor.
 
#include <memory>
#include <type_traits>
 
#include <boost/pfr/core.hpp>
 
#include <userver/storages/clickhouse/impl/block_wrapper_fwd.hpp>
#include <userver/storages/clickhouse/io/impl/validate.hpp>
 
#include <userver/storages/clickhouse/io/result_mapper.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace storages::clickhouse {
 
/// Thin wrapper over underlying block of data, returned by
/// storages::clickhouse::Cluster Execute methods
///
/// ## Usage example:
///
/// @snippet storages/tests/execute_chtest.cpp  Sample CppToClickhouse specialization
///
/// @snippet storages/tests/execute_chtest.cpp  Sample ExecutionResult usage
class ExecutionResult final {
public:
    explicit ExecutionResult(impl::BlockWrapperPtr);
    ExecutionResult(ExecutionResult&&) noexcept;
    ~ExecutionResult();
 
    /// Returns number of columns in underlying block.
    size_t GetColumnsCount() const;
 
    /// Returns number of rows in underlying block columns.
    size_t GetRowsCount() const;
 
    /// Converts underlying block to strongly-typed struct of vectors.
    /// See @ref scripts/docs/en/userver/clickhouse/io.md for better understanding of `T`'s requirements.
    template <typename T>
    T As() &&;
 
    /// Converts underlying block to iterable of strongly-typed struct.
    /// See @ref scripts/docs/en/userver/clickhouse/io.md for better understanding of `T`'s requirements.
    template <typename T>
    auto AsRows() &&;
 
    /// Converts underlying block to strongly-typed container.
    /// See @ref scripts/docs/en/userver/clickhouse/io.md for better understanding
    /// of `Container::value_type`'s requirements.
    template <typename Container>
    Container AsContainer() &&;
 
private:
    impl::BlockWrapperPtr block_;
};
 
template <typename T>
T ExecutionResult::As() && {
    UASSERT(block_);
    T result{};
    io::impl::ValidateColumnsMapping(result);
    io::impl::ValidateColumnsCount<T>(GetColumnsCount());
 
    using MappedType = typename io::CppToClickhouse<T>::mapped_type;
    io::ColumnsMapper<MappedType> mapper{*block_};
 
    boost::pfr::for_each_field(result, mapper);
 
    return result;
}
 
template <typename T>
auto ExecutionResult::AsRows() && {
    UASSERT(block_);
    io::impl::ValidateRowsMapping<T>();
    io::impl::ValidateColumnsCount<T>(GetColumnsCount());
 
    return io::RowsMapper<T>{std::move(block_)};
}
 
template <typename Container>
Container ExecutionResult::AsContainer() && {
    UASSERT(block_);
    using Row = typename Container::value_type;
 
    Container result;
    if constexpr (io::traits::kIsReservable<Container>) {
        result.reserve(GetRowsCount());
    }
 
    auto rows = std::move(*this).AsRows<Row>();
    std::move(rows.begin(), rows.end(), io::traits::Inserter(result));
    return result;
}
 
}  // namespace storages::clickhouse
 
USERVER_NAMESPACE_END