Boost C++ Libraries

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;
    }
}