...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
This example assumes you have gone through the setup.
/** * This example demonstrates how to use DELETE statements * and the results::affected_rows() function. * * The program deletes an employee, given their ID, * and prints whether the deletion was successful. * * 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. * * This example uses the 'boost_mysql_examples' database, which you * can get by running db_setup.sql. */ #include <boost/mysql/any_connection.hpp> #include <boost/mysql/error_with_diagnostics.hpp> #include <boost/mysql/results.hpp> #include <boost/mysql/with_params.hpp> #include <boost/asio/awaitable.hpp> #include <boost/asio/co_spawn.hpp> #include <boost/asio/io_context.hpp> #include <cstdint> #include <iostream> #include <string> #include <string_view> namespace mysql = boost::mysql; namespace asio = boost::asio; // The main coroutine asio::awaitable<void> coro_main( std::string_view server_hostname, std::string_view username, std::string_view password, std::int64_t employee_id ) { // Create a connection. // Will use the same executor as the coroutine. mysql::any_connection conn(co_await asio::this_coro::executor); // The server host, username, password and database to use. mysql::connect_params params; params.server_address.emplace_host_and_port(std::string(server_hostname)); params.username = std::move(username); params.password = std::move(password); params.database = "boost_mysql_examples"; // Connect to the server co_await conn.async_connect(params); // Perform the deletion. mysql::results result; co_await conn.async_execute( mysql::with_params("DELETE FROM employee WHERE id = {}", employee_id), result ); // affected_rows() returns the number of rows that were affected // by the executed statement. If there was an affected row, the deletion was successful. // Note that this may not work for UPDATEs, as they may match but not affected some rows. if (result.affected_rows() != 0u) { std::cout << "Deletion successful\n"; } else { std::cout << "No employee with such ID\n"; } // 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 != 5) { std::cerr << "Usage: " << argv[0] << " <username> <password> <server-hostname> <employee-id>\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], std::stoi(argv[4])); }, // 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; } }