doc/concepts/mysql

CONCEPT
        mysql - mySQL support

DESCRIPTION
        On hosts with the mySQL package installed, the driver can be
        configured to interface with the mySQL database. If that is done,
        the driver defines the macro __MYSQL__ for LPC programs and
        activates a number of efuns.

        -- Configuration --

        Create a dedicated user in the mySQL database for the driver.
        Enter this username and password in the file pkg-mysql.c, function
        mysql_real_connect(), and compile the driver (the username and
        password are built into the driver for security reasons). If you
        choose to not create either a username and/or a password, leave the
        corresponding entry at 0.

        Use mysqladmin to create any databases you want to provide - the
        names are later used in the efun db_connect() to connect to
        the databases.


        -- Usage --

        The idea behind SQL-support is that you can swap large amounts of
        data into a database where it can be accessed very easily.
        As mySQL "limits" the number of connections to 100 and as every
        connection to the mySQL-server takes time, you should use
        database serverobjects in your MUD which constantly keep the
        connection to the mySQL-server.

        To connect to your mySQL-server, use the efun db_connect(). It
        takes only one argument which is the name of the database (which
        must exist). The return-value of db_connect() is an integer
        representing the unique handle to the database with which you will
        identify your connection later.

        To send or retrieve data from this connection, use db_exec(). The
        first parameter for all efuns dealing with an open connection is
        always the handle and so is the first argument the handle and the
        second one the command you want to issue. The return-value is
        either 0 if there was an error in your command (this can have
        various reasons), otherwise your handle is returned again. A typical
        SQL-statement to retrieve data would be like this:

                select aliases.command from aliases where (name = 'mario' AND
                  alias regexp 'l.*')

        As you know, mySQL accepts either " or ' to classify strings for
        parameters.  Most likely, you will pass variables and don't know
        whether they contain one or more of these key-chars (or even other
        chars that need to be converted). mySQL provides a function for
        converting just any string into an acceptable argument and this is
        implemented in db_conv_string().

        So the above example with variables looks like this:

                select aliases.command from aliases where (name ='"+
                  db_conv_string(name)+"' AND alias regexp '"+
                  db_conv_string(mask)+"')

        I left out the db_exec()-stuff, more complete examples will follow.

        After you initiated a statement that should return rows from the
        database, use db_fetch() to retrieve the data. db_fetch() returns
        the data row by row and not all at once. You need to call it until
        it returns 0. THIS IS IMPORTANT! If stop calling db_fetch() before
        it reaches the end of data, serious inconsistencies can happen.

        If you used a DELETE- or UPDATE-statement, you cannot call db_fetch(),
        but you might be interested in the number of deleted/changed rows
        which can be queried with db_affected_rows().

        After all operations are done in the database, you should use
        db_close() to close the connection again. If you are using a
        database-server-concept, place it in the remove()-function.

        The SQL-efuns have some built-in optimization-features to speed up
        often used connections. To get a list of all open connections to the
        mySQL-server, use db_handles() which returns an array of integers
        with all open handles.


        -- Security --

        Most SQL efuns (unless execute by the master or the simul-efun object)
        trigger a privilege_violation ("mysql", "<efun_name>"). If a more
        finegrained control is desired, overload the individual efuns with a
        nomask simul-efun.

        The unprivileged efuns are:

          db_conv_string()


        -- Caveats --

        The driver enables automatic reconnects on the database connections.
        This means that if a connection is lost - the most common case for
        this is timeouts, which by default happen after 28800 seconds of
        inactivity - an attempt will be made to establish a new connection to
        the database server. When that happens, all session state (temprary
        tables and state changes from SET statements) will be lost. It's best
        not to rely on such state.

EXAMPLE
        A simple server to store aliases could be implemented like this:

        /*
        **  CREATION:
        **
        **  create table aliases (
        **      name varchar(15) not NULL,
        **      alias varchar(20) not NULL,
        **      command varchar(255) not NULL,
        **      primary key (name, alias));
        */

        #define DATABASE "mud"

        private int handle;

        public void create()
        {
            handle = db_connect(DATABASE);
        }

        public int remove()
        {
            if ( handle )
                db_close(handle);
            destruct(ME);
            return !ME;
        }

        public int AddAlias(string alias, string command, object ob)
        {
            if ( !handle )
                handle = db_connect(DATABASE);
            if ( !db_exec(handle,
                          "insert into aliases (name, alias, command) values "
                          "('" + getuid(ob) + "','" + db_conv_string(alias)
                               + "','"+
                          db_conv_string(command) + "')") )
                return -1;
            return 1;
        }

        public int RemoveAlias(string alias, object ob)
        {
            int res;

            if ( !handle )
                handle = db_connect(DATABASE);
            res = db_exec(handle,
                          "delete from aliases where (name = '"+
                          getuid(ob) + "' AND alias = '"
                                     + db_conv_string(alias)+
                          "')");
            if ( !res )
                return 0;
            res = db_affected_rows(handle);
            return (res > 0)?1:-1;
        }

        public mixed *QueryAliases(string mask, object ob)
        {
            mixed *result;
            string *tmp;

            if ( !handle )
                handle = db_connect(DATABASE);
            if ( !db_exec(handle,
                          "select aliases.alias, aliases.command from aliases where "
                          "(name = '" + getuid(ob)+
                          "' AND alias regexp '" + db_conv_string(mask) + "')") )
                return ({ });
            result = ({ });
            while ( sizeof(tmp = db_fetch(handle)) )
                result += ({ tmp });
            return result;
        }

        public string QueryAlias(string alias, object ob)
        {
            mixed *result;
            string *tmp;

            if ( !handle )
                handle = db_connect(DATABASE);
            if ( !db_exec(handle,
                          "select aliases.command from aliases where "
                          "(name = '" + getuid(ob)+
                          "' AND alias = '" + db_conv_string(alias) + "')") )
                return 0;
            result = ({ });
            while ( sizeof(tmp = db_fetch(handle)) )
                result += tmp;
            return sizeof(result)?result[0]:0;
        }


AUTHOR
        Mark Daniel Reidel and others.

HISTORY
        mySQL support was added as a package in 3.2.8 and became and
        integral driver part in 3.2.9.
        LDMud 3.2.11 added a privilege_violation() call for each efun.

SEE ALSO
        pgsql(C), db_affected_rows(E), db_conv_string(E), db_close(E),
        db_connect(E), db_exec(E), db_fetch(E), db_handles(E),
        db_insert_id(E), db_coldefs(E), db_error(E), privilege_violation(A)