# mysqlpp::Connection Class Reference

Manages the connection to the database server. More...

`#include <connection.h>`

Inheritance diagram for mysqlpp::Connection:

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Collaboration diagram for mysqlpp::Connection:

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List of all members.

## Public Member Functions

| Connection (bool te=true)
| Create object without connecting to the database server.
| Connection (const char *db, const char *server=0, const char *user=0, const char *password=0, unsigned int port=0)
| Create object and connect to database server in one step.
| Connection (const Connection &other)
| Establish a new connection using the same parameters as an existing connection.
virtual | ~Connection ()
| Destroy object.
std::string | client_version () const
| Get version of library underpinning the current database driver.
virtual bool | connect (const char *db=0, const char *server=0, const char *user=0, const char *password=0, unsigned int port=0)
| Connect to database after object is created.
bool | connected () const
| Returns true if connection was established successfully.
ulonglong | count_rows (const std::string &table)
| Returns the number of rows in a table.
bool | create_db (const std::string &db)
| Ask the database server to create a database.
void | disconnect ()
| Drop the connection to the database server.
DBDriver * | driver ()
| Returns a reference to the current database driver.
bool | drop_db (const std::string &db)
| Asks the database server to drop (destroy) a database.
int | errnum ()
| Return last error number associated with this connection.
const char * | error () const
| Return error message for last error associated with this connection.
std::string | ipc_info () const
| Get information about the IPC connection to the database server.
bool | kill (unsigned long tid) const
| Kill a database server thread.
| operator private_bool_type () const
| Test whether any error has occurred within the object.
Connection & | operator= (const Connection &rhs)
| Copy an existing Connection object's state into this object.
bool | ping ()
| "Pings" the database server
int | protocol_version () const
| Returns version number of the protocol the database driver uses to communicate with the server.
Query | query (const char *qstr=0)
| Return a new query object.
Query | query (const std::string &qstr)
| Return a new query object.
bool | select_db (const std::string &db)
| Change to a different database managed by the database server we are connected to.
std::string | server_version () const
| Get the database server's version string.
bool | set_option (Option *o)
| Sets a connection option.
bool | shutdown ()
| Ask database server to shut down.
std::string | server_status () const
| Returns information about database server's status.
unsigned long | thread_id ()
| Returns the database server's thread ID for this connection.

## Static Public Member Functions

static bool | thread_aware ()
| Returns true if both MySQL++ and database driver we're using were compiled with thread awareness.
static void | thread_end ()
| Tells the underlying database driver that this thread is done using the library.
static bool | thread_start ()
| Tells the underlying database driver that the current thread is now using its services.

## Protected Member Functions

void | build_error_message (const char *core)
| Build an error message in the standard form used whenever one of the methods can't succeed because we're not connected to the database server.
void | copy (const Connection &other)
| Establish a new connection as a copy of an existing one.
bool | parse_ipc_method (const char *server, std::string &host, unsigned int &port, std::string &socket_name)
| Extract elements from the server parameter in formats suitable for passing to DBDriver::connect().

## Protected Attributes

std::string | error_message_
| MySQL++ specific error, if any.

## Detailed Description

Manages the connection to the database server.

This class is a thick wrapper around DBDriver, adding high-level error handling, utility functions, and abstraction away from underlying C API details.

## Constructor & Destructor Documentation

mysqlpp::Connection::Connection | ( | bool | te = `true` | ) |

Create object without connecting to the database server.

Parameters:

  | te | if true, exceptions are thrown on errors

mysqlpp::Connection::Connection | ( | const char * | db,
|  | const char * | server = `0`,
|  | const char * | user = `0`,
|  | const char * | password = `0`,
|  | unsigned int | port = `0` |
| ) |  |  |

Create object and connect to database server in one step.

This constructor allows you to most fully specify the options used when connecting to the database server.

Parameters:

  | db | name of database to select upon connection
  | server | specifies the IPC method and parameters for contacting the server; see below for details
  | user | user name to log in under, or 0 to use the user name this program is running under
  | password | password to use when logging in
  | port | TCP port number database server is listening on, or 0 to use default value; note that you may also give this as part of the `server` parameter

The server parameter can be any of several different forms:

- 0: Let the database driver decide how to connect; usually some sort of localhost IPC method.
- ".": On Windows, this means named pipes, if the server supports it
- "/some/domain/socket/path": If the passed string doesn't match one of the previous alternatives and we're on a system that supports Unix domain sockets, MySQL++ will test it to see if it names one, and use it if we have permission.
- "host.name.or.ip:port": If the previous test fails, or if the system doesn't support Unix domain sockets at all, it assumes the string is some kind of network address, optionally followed by a colon and port. The name can be in dotted quad form, a host name, or a domain name. The port can either be a TCP/IP port number or a symbolic service name. If a port or service name is given here and a nonzero value is passed for the `port` parameter, the latter takes precedence.

mysqlpp::Connection::Connection | ( | const Connection & | other | ) |

Establish a new connection using the same parameters as an existing connection.

Parameters:

  | other | existing Connection object

## Member Function Documentation

bool mysqlpp::Connection::connect | ( | const char * | db = `0`,
|  | const char * | server = `0`,
|  | const char * | user = `0`,
|  | const char * | password = `0`,
|  | unsigned int | port = `0` |
| ) |  |  | `[virtual]`

Connect to database after object is created.

It's better to use the connect-on-create constructor if you can. See its documentation for the meaning of these parameters.

If you call this method on an object that is already connected to a database server, the previous connection is dropped and a new connection is established.

bool mysqlpp::Connection::connected | ( |  | ) | const

Returns true if connection was established successfully.

Returns:
  true if connection was established successfully

void mysqlpp::Connection::copy | ( | const Connection & | other | ) | `[protected]`

Establish a new connection as a copy of an existing one.

Parameters:

  | other | the connection to copy

ulonglong mysqlpp::Connection::count_rows | ( | const std::string & | table | ) |

Returns the number of rows in a table.

Parameters:

  | table | name of table whose rows you want counted

This is syntactic sugar for a `SELECT` `COUNT(*)` `FROM` `table` SQL query.

bool mysqlpp::Connection::create_db | ( | const std::string & | db | ) |

Ask the database server to create a database.

Parameters:

  | db | name of database to create

Returns:
  true if database was created successfully

bool mysqlpp::Connection::drop_db | ( | const std::string & | db | ) |

Asks the database server to drop (destroy) a database.

Parameters:

  | db | name of database to destroy

Returns:
  true if database was dropped successfully

const char * mysqlpp::Connection::error | ( |  | ) | const

Return error message for last error associated with this connection.

Returns either a MySQL++-specific error message if one exists, or one from the current database driver otherwise.

std::string mysqlpp::Connection::ipc_info | ( |  | ) | const

Get information about the IPC connection to the database server.

String contains info about type of connection (e.g. TCP/IP, named pipe, Unix socket...) and the server hostname.

bool mysqlpp::Connection::kill | ( | unsigned long | tid | ) | const

Kill a database server thread.

Parameters:

  | tid | ID of thread to kill

See also:
  thread_id()

mysqlpp::Connection::operator private_bool_type | ( |  | ) | const`[inline]`

Test whether any error has occurred within the object.

Allows the object to be used in bool context, like this:

            ///

Prior to MySQL++ v3, the object was always falsy when we weren't connected. Now a true return simply indicates a lack of errors. If you've been using this to test for whether the connection is still up, you need to call connected() instead.

bool mysqlpp::Connection::ping | ( |  | ) |

"Pings" the database server

Return values:

  | true | if server is responding
  | false | if either we already know the connection is down and cannot re-establish it, or if the server did not respond to the ping and we could not re-establish the connection.

Query mysqlpp::Connection::query | ( | const std::string & | qstr | ) |

Return a new query object.

Parameters:

  | qstr | initial query string

Query mysqlpp::Connection::query | ( | const char * | qstr = `0` | ) |

Return a new query object.

The returned query object is tied to this connection object, so when you call a method like execute() on that object, the query is sent to the server this object is connected to.

Parameters:

  | qstr | an optional query string for populating the new Query object

bool mysqlpp::Connection::select_db | ( | const std::string & | db | ) |

Change to a different database managed by the database server we are connected to.

Parameters:

  | db | database to switch to

Return values:

  | true | if we changed databases successfully

bool mysqlpp::Connection::set_option | ( | Option * | o | ) |

Sets a connection option.

Parameters:

  | o | pointer to any derivative of Option allocated on the heap

Objects passed to this method and successfully set will be released when this Connection object is destroyed. If an error occurs while setting the option the object will be deleted immediately.

Because there are so many Option subclasses, the actual effect of this function has a wide range. This mechanism abstracts away many things that are unrelated down at the database driver level, hiding them behind a coherent, type-safe interface.

The rules about which options can be set, when, are up to the underlying database driver. Some must be set before the connection is established because they can only be used during that connection setup process. Others can be set at any time after the connection comes up. If you get it wrong, you'll get a BadOption exception.

Return values:

  | true | if option was successfully set

unsigned long mysqlpp::Connection::thread_id | ( |  | ) |

Returns the database server's thread ID for this connection.

This has nothing to do with threading on the client side. The only thing you can do with this value is pass it to kill().

bool mysqlpp::Connection::thread_start | ( |  | ) | `[static]`

Tells the underlying database driver that the current thread is now using its services.

It's not necessary to call this from the thread that creates the connection as it's done automatically. This method exists for times when multiple threads may use this object; it allows the underlying database driver to set up any per-thread data structures it needs.

The MySQL++ user manual's chapter on threads details two major strategies for dealing with connections in the face of threads. The Connection-per-thread option frees you from ever having to call this method. The other documented strategy is to use ConnectionPool, which opens the possibility for one thread to create a connection that another uses, so you do need to call this method in that case, or with any other similar strategy.

Return values:

  | True | if there was no problem

The documentation for this class was generated from the following files:

- connection.h
- connection.cpp