...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 insert several records in a single * SQL statement using format_sql. * * The program reads a JSON file containing a list of employees * and inserts it into the employee table. It uses Boost.JSON and * Boost.Describe to parse the file. * * This example uses C++20 coroutines. If you need, you can backport * it to C++14 (required by Boost.Describe) 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_address.hpp> #include <boost/mysql/any_connection.hpp> #include <boost/mysql/error_with_diagnostics.hpp> #include <boost/mysql/results.hpp> #include <boost/mysql/sequence.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 <boost/describe/class.hpp> #include <boost/json/parse.hpp> #include <boost/json/value_to.hpp> #include <fstream> #include <iostream> #include <string> namespace asio = boost::asio; namespace mysql = boost::mysql; namespace json = boost::json; /** * We will use Boost.Describe to easily parse the JSON file * into a std::vector<employee>. The JSON file contain an array * of objects like the following: * { * "first_name": "Some string", * "last_name": "Some other string", * "company_id": "String", * "salary": 20000 * } */ struct employee { std::string first_name; std::string last_name; std::string company_id; std::int64_t salary; // in dollars per year }; // Adds reflection capabilities to employee. Required by the JSON parser. // Boost.Describe requires C++14 BOOST_DESCRIBE_STRUCT(employee, (), (first_name, last_name, company_id, salary)) // Reads a file into memory static std::string read_file(const char* file_name) { std::ifstream ifs(file_name); if (!ifs) throw std::runtime_error("Cannot open file: " + std::string(file_name)); return std::string(std::istreambuf_iterator<char>(ifs), std::istreambuf_iterator<char>()); } // The main coroutine asio::awaitable<void> coro_main( std::string_view server_hostname, std::string_view username, std::string_view password, const std::vector<employee>& employees ) { // Create a 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); // A function describing how to format a single employee object. Used with mysql::sequence. auto format_employee_fn = [](const employee& emp, mysql::format_context_base& ctx) { // format_context_base can be used to build query strings incrementally. // Used internally by the sequence() formatter. // format_sql_to expands a format string, replacing {} fields, // and appends the result to the passed context. // When formatted, strings are quoted and escaped as string literals. // ints are formatted as number literals. mysql::format_sql_to( ctx, "({}, {}, {}, {})", emp.first_name, emp.last_name, emp.company_id, emp.salary ); }; // Compose and execute the batch INSERT. When passed to execute(), with_params // replaces placeholders ({}) by actual parameter values before sending the query to the server. // When inserting two employees, something like the following may be generated: // INSERT INTO employee (first_name, last_name, company_id, salary) // VALUES ('John', 'Doe', 'HGS', 20000), ('Rick', 'Smith', 'LLC', 50000) mysql::results result; co_await conn.async_execute( mysql::with_params( "INSERT INTO employee (first_name, last_name, company_id, salary) VALUES {}", mysql::sequence(std::ref(employees), format_employee_fn) ), result ); // 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> <input-file>\n"; exit(1); } // Read our JSON file into memory auto contents = read_file(argv[4]); // Parse the JSON. json::parse parses the string into a DOM, // and json::value_to validates the JSON schema, parsing values into employee structures auto values = json::value_to<std::vector<employee>>(json::parse(contents)); // We need one employee, at least if (values.empty()) { std::cerr << "Input file should contain one employee, at least\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], values); }, // 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 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; } }