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Reading DATE, DATETIME via mysqlx (MySQL Connector/C++ 8.0 X DevAPI)
Posted by: Kira Backes
Date: October 19, 2022 07:53AM

Since this is still not implemented into the C++ Connector we developed the following C++20 helper methods for production use with mysqlx (MySQL Connector/C++ 8.0 X DevAPI) to properly read DATE, DATETIME and TIMESTAMP fields:

#pragma once

#include <vector>
#include <cstddef>
#include <chrono>
#include <mysqlx/xdevapi.h>

namespace mysqlx {

static inline std::vector<uint64_t>
mysqlx_raw_as_u64_vector(const mysqlx::Value& in_value)
{
std::vector<uint64_t> out;

const auto bytes = in_value.getRawBytes();
auto ptr = reinterpret_cast<const std::byte*>(bytes.first);
auto end = reinterpret_cast<const std::byte*>(bytes.first) + bytes.second;

while (ptr != end) {
static constexpr std::byte carry_flag{0b1000'0000};
static constexpr std::byte value_mask{0b0111'1111};

uint64_t v = 0;
uint64_t shift = 0;
bool is_carry;
do {
auto byte = *ptr;
is_carry = (byte & carry_flag) == carry_flag;
v |= std::to_integer<uint64_t>(byte & value_mask) << shift;

++ptr;
shift += 7;
} while (is_carry && ptr != end && shift <= 63);

out.push_back(v);
}

return out;
}

static inline std::chrono::year_month_day
read_date(const mysqlx::Value& value)
{
const auto vector = mysqlx_raw_as_u64_vector(value);
if (vector.size() < 3)
throw std::out_of_range{"Value is not a valid DATE"};

return std::chrono::year{static_cast<int>(vector.at(0))} / static_cast<int>(vector.at(1)) / static_cast<int>(vector.at(2));
}

static inline std::chrono::system_clock::time_point
read_date_time(const mysqlx::Value& value)
{
const auto vector = mysqlx_raw_as_u64_vector(value);
if (vector.size() < 3)
throw std::out_of_range{"Value is not a valid DATETIME"};

auto ymd = std::chrono::year{static_cast<int>(vector.at(0))} / static_cast<int>(vector.at(1)) / static_cast<int>(vector.at(2));
auto sys_days = std::chrono::sys_days{ymd};

auto out = std::chrono::system_clock::time_point(sys_days);

auto it = vector.begin() + 2;
auto end = vector.end();

if (++it == end)
return out;
out += std::chrono::hours{*it};

if (++it == end)
return out;
out += std::chrono::minutes{*it};

if (++it == end)
return out;
out += std::chrono::seconds{*it};

if (++it == end)
return out;
out += std::chrono::microseconds{*it};

return out;
}

} //namespace



Which can then be used as follows:



auto row = table.select("datetime", "date").execute().fetchOne();
auto time_point = read_date_time(row[0]);
auto year_month_day = read_date(row[1]);



rgds Kira

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Reading DATE, DATETIME via mysqlx (MySQL Connector/C++ 8.0 X DevAPI)
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