Msql.pm

NAME

Msql - Perl interface to the mSQL database

SYNOPSIS

use Msql; $dbh = Msql->connect; $dbh = Msql->connect($host); $dbh = Msql->connect($host, $database); $dbh->selectdb($database); @arr = $dbh->listdbs; @arr = $dbh->listtables; $quoted_string = $dbh->quote($unquoted_string); $error_message = $dbh->errmsg; $sth = $dbh->listfields($table); $sth = $dbh->query($sql_statement); @arr = $sth->fetchrow; %hash = $sth->fetchhash; $sth->dataseek($row_number); $sth->as_string; @indices = $sth->listindices; # only in mSQL 2.0 @arr = $dbh->listindex($table,$index); # only in mSQL 2.0

DESCRIPTION

This package is designed as close as possible to its C API counterpart. The manual that comes with mSQL describes most things you need. Due to popular demand it was decided though, that this interface does not use StudlyCaps (see below).

Internally you are dealing with the two classes Msql and Msql::Statement. You will never see the latter, because you reach it through a statement handle returned by a query or a listfields statement. The only class you name explicitly is Msql. It offers you the connect command:

$dbh = Msql->connect; $dbh = Msql->connect($host); $dbh = Msql->connect($host, $database);

This connects you with the desired host/database. With no argument or with an empty string as the first argument it connects to the UNIX socket (usually /dev/msql), which has a much better performance than the TCP counterpart. A database name as the second argument selects the chosen database within the connection. The return value is a database handle if the connect succeeds, otherwise the return value is undef.

You will need this handle to gain further access to the database.

$dbh->selectdb($database);

If you have not chosen a database with the connect command, or if you want to change the connection to a different database using a database handle you have got from a previous connect, then use selectdb.

$sth = $dbh->listfields($table); $sth = $dbh->query($sql_statement);

These two work rather similar as descibed in the mSQL manual. They return a statement handle which lets you further explore what the server has to tell you. On error the return value is undef. The object returned by listfields will not know about the size of the table, so a numrows() on it will return the string ``N/A'';

@arr = $dbh->listdbs(); @arr = $dbh->listtables;

An array is returned that contains the requested names without any further information.

@arr = $sth->fetchrow;

returns an array of the values of the next row fetched from the server. Similar does

%hash = $sth->fetchhash;

return a complete hash. The keys in this hash are the column names of the table, the values are the table values. Be aware, that when you have a table with two identical column names, you will not be able to use this method without trashing one column. In such a case, you should use the fetchrow method.

$sth->dataseek($row_number);

lets you specify a certain offset of the data associated with the statement handle. The next fetchrow will then return the appropriate row (first row being 0).

No close statement

Whenever the scalar that holds a database or statement handle loses its value, Msql chooses the appropriate action (frees the result or closes the database connection). So if you want to free the result or close the connection, choose to do one of the following:

undef the handle
use the handle for another purpose
let the handle run out of scope
exit the program.

Error messages

A static method in the Msql class is ->errmsg(), which returns the current value of the msqlErrMsg variable that is provided by the C API. There's also a global variable $Msql::db_errstr, which always holds the last error message. The former is reset with the next executed command, the latter not.

The `-w` switch

With Msql the -w switch is your friend! If you call your perl program with the -w switch you get the warnings from ->errmsg on STDERR. This is a handy method to get the error messages from the msql server without coding it into your program.

If you want to know in greater detail what's going on, set the environment variables that are described in David's manual. David's debugging aid is excellent, there's nothing to be added.

If you want to use the -w switch but do not want to see the error messages from the msql daemon, you can set the variable $Msql::QUIET to some true value, and they will be supressed.

->quote($str)

returns the argument enclosed in single ticks ('') with any special character escaped according to the needs of the API. Currently this means, any single tick within the string is escaped with a backslash and backslashes are doubled. Currently (as of msql-1.0.16) the API does not allow to insert binary nulls into tables. The quote method does not fix this deficiency, so use it at your own risk for binary nulls.

Metadata

Now lets reconsider the above methods with regard to metadata.

Database Handle

As said above you get a database handle with

$dbh = Msql->connect($host, $database);

The database handle knows about the socket, the host, and the database it is connected to.

You get at the three values with the methods

$scalar = $dbh->sock; $scalar = $dbh->host; $scalar = $dbh->database;

database returns undef, if you have connected without or with only one argument.

Statement Handle

Two constructor methods return a statement handle:

$sth = $dbh->listfields($table); $sth = $dbh->query($sql_statement);

$sth knows about all metadata that are provided by the API:

$scalar = $sth->numrows; $scalar = $sth->numfields; @arr = $sth->table; the names of the tables of each column @arr = $sth->name; the names of the columns @arr = $sth->type; the type of each column, defined in msql.h and accessible via Msql::CHAR_TYPE, &Msql::INT_TYPE, &Msql::REAL_TYPE, @arr = $sth->isnotnull; array of boolean @arr = $sth->isprikey; array of boolean @arr = $sth->length; array of the length of each field in bytes

The six last methods return an array in array context and an array reference (see the perlref manpage and the perlldsc manpage for details) when called in a scalar context. The scalar context is useful, if you need only the name of one column, e.g.

$name_of_third_column = $sth->name->[2]

which is equivalent to

@all_column_names = $sth->name; $name_of_third_column = $all_column_names[2];

New in mSQL 2.0

The query() function in the API returns the number of rows affected by a query. To cite the mSQL API manual, this means...

If the return code is greater than 0, not only does it imply success, it also indicates the number of rows "touched" by the query (i.e. the number of rows returned by a SELECT, the number of rows modified by an update, or the number of rows removed by a delete).

As we are returning a statement handle on selects, we can easily check the number of rows returned. For non-selects we behave just the same as mSQL-2.

To find all indices associated with a table you can call the listindices() method on a statement handle. To find out the columns included in an index, you can call the listindex($table,$index) method on a database handle.

There are a few new column types in mSQL 2. Access their numeric value with the functions Msql::IDENT_TYPE, Msql::IDX_TYPE, and Msql::TEXT_TYPE.

You cannot talk to a 1.0 server with a 2.0 client.

You cannot link to a 1.0 library and to a 2.0 library I-I switch in perl is for.

Everything else seems to remain backwards compatible.

@EXPORT

For historical reasons the constants CHAR_TYPE, INT_TYPE, and REAL_TYPE are in @EXPORT instead of @EXPORT_OK. This means, that you always have them imported into your namespace. I consider it a bug, but not such a serious one, that I intend to break old programs by moving them into EXPORT_OK.

Connecting to a different port

The mSQL API allows you to interface to a different port than the default that is compiled into your copy. To use this feature you have to set the environment variable MSQL_TCP_PORT. You can do so at any time in your program with the command

$ENV{'MSQL_TCP_PORT'} = 1234; # or 1112 or 1113 or 4333 or 4334

Any subsequent connect() will establish a connection to the specified port.

For connect()s to the UNIX socket of the local machine use MSQL_UNIX_PORT instead.

Displaying whole tables in one go

A handy method to show the complete contents of a statement handle is the as_string method. This works similar to the msql monitor with a few exceptions:

the width of a column: is calculated by examining the width of all entries in that column
control characters: are mapped into their backslashed octal representation
backslashes: are doubled (\\ instead of \)
numeric values: are adjusted right (both integer and floating point values)

The differences are illustrated by the following table:. Input to msql (a real carriage return here replaced with ^M):

CREATE TABLE demo ( first_field CHAR(10), second_field INT ) \g INSERT INTO demo VALUES ('new line',2)\g INSERT INTO demo VALUES ('back\\slash',1)\g INSERT INTO demo VALUES ('cr^Mcrnl nl',3)\g

Output of msql:

+-------------+--------------+ | first_field | second_field | +-------------+--------------+ | new line | 2 | | back\slash | 1 | crnlr nl | 3 | +-------------+--------------+

Output of pmsql:

+----------------+------------+ |first_field |second_field| +----------------+------------+ |new\012line | 2| |back\\slash | 1| |cr\015crnl\012nl| 3| +----------------+------------+

Version information

The version of MsqlPerl is always stored in $Msql::VERSION as it is perl standard.

The mSQL API implements methods to access some internal configuration parameters: gethostinfo, getserverinfo, and getprotoinfo. All three are available both as class methods or via a database handle. But under no circumstances they are associated with a database handle. All three return global variables that reflect the last connect() command within the current program. This means, that all three return empty strings or zero before the first call to connect().

Administration

shutdown, creatdb, dropdb, reloadacls are all accessible via a database handle and implement the corresponding methods to what msqladmin does.

StudlyCaps

Real Perl Programmers (C) usually don't like to type ListTables but prefer list_tables or listtables. The mSQL API uses StudlyCaps everywhere and so did early versions of MsqlPerl. Beginning with $VERSION 1.06 all methods are internally in lowercase, but may be written however you please. Case is ignored and you may use the underline to improve readability.

The price for using different method names is neglectible. Any method name you use that can be transformed into a known one, will only be defined once within a program and will remain an alias until the program terminates. So feel free to run fetch_row or connecT or ListDBs as in your old programs. These, of course, will continue to work.

PREREQUISITES

mSQL is a database server and an API library written by David Hughes. To use the adaptor you definitely have to install these first.

AUTHOR

andreas koenig koenig@franz.ww.TU-Berlin.DE

The -w switch

->quote($str)

@EXPORT

The `-w` switch