...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 prepare, execute * and deallocate prepared statements. This program retrieves * all employees in a company, given its ID. * * 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/results.hpp> #include <boost/mysql/row_view.hpp> #include <boost/mysql/statement.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> #include <string_view> 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, std::string_view company_id ) { // 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); // Prepared statements can be used to execute queries with untrusted // parameters securely. They are an option to mysql::with_params, // but work server-side. // They are more complex but can yield more efficiency when retrieving // lots of numeric data, or when executing the same query several times with the same parameters. // Ask the server to prepare a statement and retrieve its handle mysql::statement stmt = co_await conn.async_prepare_statement( "SELECT first_name, last_name, salary FROM employee WHERE company_id = ?" ); // Execute the statement. bind() must be passed as many parameters (number of ?) // as the statement has. bind() packages the statement handle with the parameters, // and async_execute sends them to the server mysql::results result; co_await conn.async_execute(stmt.bind(company_id), result); for (mysql::row_view employee : result.rows()) print_employee(employee); // We can execute stmt as many times as we want, potentially with different // parameters, without the need to re-prepare it. // Once we're done with a statement, we can close it, to deallocate it from the server. // Closing the connection will also deallocate active statements, so this is not // strictly required here, but it's shown for completeness. // This can be relevant if you're using long-lived sessions. // Note that statement's destructor does NOT close the statement. co_await conn.async_close_statement(stmt); // 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> <company-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], 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; } }