1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
|
//
// Copyright (c) 2019-2025 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)
//
#include <boost/asio/awaitable.hpp>
#ifdef BOOST_ASIO_HAS_CO_AWAIT
//[example_deletes
/**
* This example demonstrates how to use DELETE statements
* and the results::affected_rows() function.
*
* The program deletes an employee, given their ID,
* and prints whether the deletion was successful.
*
* 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.
*
* 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/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 <cstdint>
#include <iostream>
#include <string>
#include <string_view>
namespace mysql = boost::mysql;
namespace asio = boost::asio;
// The main coroutine
asio::awaitable<void> coro_main(
std::string_view server_hostname,
std::string_view username,
std::string_view password,
std::int64_t employee_id
)
{
// Create a connection.
// Will use the same executor as the coroutine.
mysql::any_connection conn(co_await asio::this_coro::executor);
// The server host, username, password and database to use.
mysql::connect_params params;
params.server_address.emplace_host_and_port(std::string(server_hostname));
params.username = std::move(username);
params.password = std::move(password);
params.database = "boost_mysql_examples";
// Connect to the server
co_await conn.async_connect(params);
// Perform the deletion.
mysql::results result;
co_await conn.async_execute(
mysql::with_params("DELETE FROM employee WHERE id = {}", employee_id),
result
);
// affected_rows() returns the number of rows that were affected
// by the executed statement. If there was an affected row, the deletion was successful.
// Note that this may not work for UPDATEs, as they may match but not affected some rows.
if (result.affected_rows() != 0u)
{
std::cout << "Deletion successful\n";
}
else
{
std::cout << "No employee with such ID\n";
}
// 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> <employee-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], std::stoi(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;
}
}
//]
#else
#include <iostream>
int main()
{
std::cout << "Sorry, your compiler doesn't have the required capabilities to run this example"
<< std::endl;
}
#endif
|
