mysql/example/2_simple/multi_function.cpp

//
// Copyright (c) 2019-2025 Ruben Perez Hidalgo (rubenperez038 at gmail dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#include <boost/asio/awaitable.hpp>
#ifdef BOOST_ASIO_HAS_CO_AWAIT

//[example_multi_function

/**
 * This example demonstrates how to run multi-function operations
 * to dump an entire table to stdout, reading rows in batches.
 *
 * It uses C++20 coroutines. If you need, you can backport
 * it to C++11 by using callbacks, asio::yield_context
 * or sync functions instead of coroutines.
 */

#include <boost/mysql/any_connection.hpp>
#include <boost/mysql/error_with_diagnostics.hpp>
#include <boost/mysql/execution_state.hpp>
#include <boost/mysql/row_view.hpp>
#include <boost/mysql/rows_view.hpp>

#include <boost/asio/awaitable.hpp>
#include <boost/asio/co_spawn.hpp>
#include <boost/asio/io_context.hpp>
#include <boost/asio/this_coro.hpp>

#include <iostream>

namespace mysql = boost::mysql;
namespace asio = boost::asio;

void print_employee(mysql::row_view employee)
{
    std::cout << "Employee '" << employee.at(0) << " "   // first_name (string)
              << employee.at(1) << "' earns "            // last_name  (string)
              << employee.at(2) << " dollars yearly\n";  // salary     (double)
}

// The main coroutine
asio::awaitable<void> coro_main(
    std::string_view server_hostname,
    std::string_view username,
    std::string_view password
)
{
    // Create a connection. It will use the same executor as our coroutine
    mysql::any_connection conn(co_await asio::this_coro::executor);

    // The hostname, username, password and database to use
    mysql::connect_params params;
    params.server_address.emplace_host_and_port(std::string(server_hostname));
    params.username = username;
    params.password = password;
    params.database = "boost_mysql_examples";

    // Connect to the server
    co_await conn.async_connect(params);

    // Start our query as a multi-function operation.
    // This will send the query for execution but won't read the rows.
    // An execution_state keep tracks of the operation.
    mysql::execution_state st;
    co_await conn.async_start_execution("SELECT first_name, last_name, salary FROM employee", st);

    // st.should_read_rows() returns true while there are more rows to read.
    // Use async_read_some_rows to read a batch of rows.
    // This function tries to minimize copies. employees is a view
    // object pointing into the connection's internal buffers,
    // and is valid until you start the next async operation.
    while (st.should_read_rows())
    {
        mysql::rows_view employees = co_await conn.async_read_some_rows(st);
        for (auto employee : employees)
            print_employee(employee);
    }

    // Notify the MySQL server we want to quit, then close the underlying connection.
    co_await conn.async_close();
}

void main_impl(int argc, char** argv)
{
    if (argc != 4)
    {
        std::cerr << "Usage: " << argv[0] << " <username> <password> <server-hostname>\n";
        exit(1);
    }

    // Create an I/O context, required by all I/O objects
    asio::io_context ctx;

    // Launch our coroutine
    asio::co_spawn(
        ctx,
        [=] { return coro_main(argv[3], argv[1], argv[2]); },
        // If any exception is thrown in the coroutine body, rethrow it.
        [](std::exception_ptr ptr) {
            if (ptr)
            {
                std::rethrow_exception(ptr);
            }
        }
    );

    // Calling run will actually execute the coroutine until completion
    ctx.run();

    std::cout << "Done\n";
}

int main(int argc, char** argv)
{
    try
    {
        main_impl(argc, argv);
    }
    catch (const boost::mysql::error_with_diagnostics& err)
    {
        // Some errors include additional diagnostics, like server-provided error messages.
        // Security note: diagnostics::server_message may contain user-supplied values (e.g. the
        // field value that caused the error) and is encoded using to the connection's character set
        // (UTF-8 by default). Treat is as untrusted input.
        std::cerr << "Error: " << err.what() << ", error code: " << err.code() << '\n'
                  << "Server diagnostics: " << err.get_diagnostics().server_message() << std::endl;
        return 1;
    }
    catch (const std::exception& err)
    {
        std::cerr << "Error: " << err.what() << std::endl;
        return 1;
    }
}

//]

#else

#include <iostream>

int main()
{
    std::cout << "Sorry, your compiler doesn't have the required capabilities to run this example"
              << std::endl;
}

#endif