...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 shows how to use the static interface to parse * the results of a query into a C++ struct. * Like the previous tutorial, given an employee ID, * it prints their full name. * * It uses Boost.Pfr for reflection, which requires C++20. * You can backport it to C++14 if you need by using Boost.Describe. * * 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/pfr.hpp> #include <boost/mysql/static_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 <boost/asio/this_coro.hpp> #include <cstdint> #include <exception> #include <iostream> #include <string> #include <string_view> namespace mysql = boost::mysql; namespace asio = boost::asio; void print_employee(std::string_view first_name, std::string_view last_name) { std::cout << "Employee's name is: " << first_name << ' ' << last_name << std::endl; } // Should contain a member for each field of interest present in our query. // Declaration order doesn't need to match field order in the query. // Field names should match the ones in our query struct employee { std::string first_name; std::string last_name; }; asio::awaitable<void> coro_main( std::string_view server_hostname, std::string_view username, std::string_view password, std::int64_t employee_id ) { // Represents a connection to the MySQL server. // The connection will use the same executor as the 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); // Using static_results will parse the result of our query // into instances of the employee type. Fields will be matched // by name, instead of by position. // pfr_by_name tells the library to use Boost.Pfr for reflection, // and to match fields by name. mysql::static_results<mysql::pfr_by_name<employee>> result; // Execute the query with the given parameters, performing the required // escaping to prevent SQL injection. co_await conn.async_execute( mysql::with_params("SELECT first_name, last_name FROM employee WHERE id = {}", employee_id), result ); // Did we find an employee with that ID? if (result.rows().empty()) { std::cout << "Employee not found" << std::endl; } else { // Print the retrieved details const employee& emp = result.rows()[0]; print_employee(emp.first_name, emp.last_name); } // Close the 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); } // The execution context, required to run I/O operations. asio::io_context ctx; // Enqueue the coroutine for execution. asio::co_spawn( // The execution context where the coroutine will run ctx, // The coroutine to run. This must be a function taking no arguments // and returning an asio::awaitable<T> [argv] { return coro_main(argv[3], argv[1], argv[2], std::stoi(argv[4])); }, // Callback to run when the coroutine completes. // If any exception is thrown in the coroutine body, propagate it to terminate the program. [](std::exception_ptr ptr) { if (ptr) { std::rethrow_exception(ptr); } } ); // Calling run will actually execute the coroutine until completion ctx.run(); } int main(int argc, char** argv) { try { main_impl(argc, argv); } catch (const 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() << '\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; } }