mysql/example/query_sync.cpp

//
// Copyright (c) 2019-2022 Ruben Perez Hidalgo (rubenperez038 at gmail dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

//[example_query_sync
#include <boost/mysql.hpp>
#include <boost/mysql/handshake_params.hpp>
#include <boost/mysql/row_view.hpp>

#include <boost/asio/io_context.hpp>
#include <boost/asio/ssl/context.hpp>
#include <boost/system/system_error.hpp>

#include <iostream>

#define ASSERT(expr)                                          \
    if (!(expr))                                              \
    {                                                         \
        std::cerr << "Assertion failed: " #expr << std::endl; \
        exit(1);                                              \
    }

/**
 * Prints an employee to std::cout. An employee here is a boost::mysql::row_view,
 * which represents a row returned by a SQL query. row_view objects are an ordered
 * collection of SQL fields, representing each value returned by the query.
 *
 * Indexing a row_view yields a boost::mysql::field_view, which is a variant-like
 * type representing a single value returned by MySQL.
 */
void print_employee(const boost::mysql::row& employee)
{
    std::cout << "Employee '" << employee[0] << " "   // first_name (type string)
              << employee[1] << "' earns "            // last_name  (type string)
              << employee[2] << " dollars yearly\n";  // salary     (type double)
}

void main_impl(int argc, char** argv)
{
    if (argc != 4)
    {
        std::cerr << "Usage: " << argv[0] << " <username> <password> <server-hostname>\n";
        exit(1);
    }

    // The I/O context to perform all operations.
    boost::asio::io_context ctx;

    /**
     * Connection parameters that tell us how to connect to the MySQL server:
     * database credentials and schema to use.
     */
    boost::mysql::handshake_params params(
        argv[1],                // username
        argv[2],                // password
        "boost_mysql_examples"  // database to use; leave empty or omit for no database
    );

    /* We will use SSL in all our examples. To enable SSL, use boost::mysql::tcp_ssl_connection.
     * MySQL 8+ default is to use an authentication method that requires SSL, so we encourage
     * you to use SSL connections if you can.
     */
    boost::asio::ssl::context ssl_ctx(boost::asio::ssl::context::tls_client);

    // Represents a single connection over TCP to a MySQL server.
    boost::mysql::tcp_ssl_connection conn(ctx, ssl_ctx);

    // To establish the connection, we need a TCP endpoint. We have a hostname,
    // so we need to perform hostname resolution. We create a resolver for this.
    boost::asio::ip::tcp::resolver resolver(ctx.get_executor());

    // Invoke the resolver's appropriate function to perform the resolution.
    const char* hostname = argv[3];
    auto endpoints = resolver.resolve(hostname, boost::mysql::default_port_string);

    /**
     * Before using the connection, we have to connect to the server by:
     *    - Establishing the TCP-level session.
     *    - Authenticating to the MySQL server. The SSL handshake is performed as part of this.
     * connection::connect takes care of both.
     */
    conn.connect(*endpoints.begin(), params);

    /**
     * To issue a SQL query to the database server, use tcp_ssl_connection::query, which takes
     * the SQL to be executed as parameter and returns a resultset object by lvalue reference.
     *
     * Resultset objects represent the result of a query.
     * They hold metadata describing the fields the resultset holds (in this case, first_name,
     * last_name and salary). Resultsets don't contain the actual data, but have methods to read it.
     *
     * We will get all employees working for 'High Growth Startup'.
     */
    const char* sql = "SELECT first_name, last_name, salary FROM employee WHERE company_id = 'HGS'";
    boost::mysql::tcp_ssl_resultset result;
    conn.query(sql, result);

    /**
     * We will use resultset::read_all(), which will read all our rows into
     * a boost::mysql::rows object. This is a matrix-like object, specialized for
     * MySQL fields. Indexing a rows object returns a row_view, which represents
     * an individual row.
     */
    boost::mysql::rows all_rows;
    result.read_all(all_rows);
    for (boost::mysql::row_view employee : all_rows)
    {
        print_employee(employee);
    }

    // We can issue any SQL statement, not only SELECTs. In this case, the returned
    // resultset will have no fields and no rows
    sql = "UPDATE employee SET salary = 10000 WHERE first_name = 'Underpaid'";
    conn.query(sql, result);
    ASSERT(
        result.meta().size() == 0
    );  // meta() returns a collection containing metadata about the query fields

    // Check we have updated our poor intern salary
    conn.query("SELECT salary FROM employee WHERE first_name = 'Underpaid'", result);
    result.read_all(all_rows);
    ASSERT(all_rows.size() == 1);
    double salary = all_rows[0][0].as_double();
    ASSERT(salary == 10000);

    // Close the connection. This notifies the MySQL we want to log out
    // and then closes the underlying socket. This operation implies a network
    // transfer and thus can fail
    conn.close();
}

int main(int argc, char** argv)
{
    try
    {
        main_impl(argc, argv);
    }
    catch (const boost::system::system_error& err)
    {
        std::cerr << "Error: " << err.what() << ", error code: " << err.code() << std::endl;
        return 1;
    }
    catch (const std::exception& err)
    {
        std::cerr << "Error: " << err.what() << std::endl;
        return 1;
    }
}

//]