Provided by: libima-dbi-perl_0.35-3_all 
NAME
Ima::DBI - Database connection caching and organization
SYNOPSIS
package Foo;
use base 'Ima::DBI';
# Class-wide methods.
Foo->set_db($db_name, $data_source, $user, $password);
Foo->set_db($db_name, $data_source, $user, $password, \%attr);
my @database_names = Foo->db_names;
my @database_handles = Foo->db_handles;
Foo->set_sql($sql_name, $statement, $db_name);
Foo->set_sql($sql_name, $statement, $db_name, $cache);
my @statement_names = Foo->sql_names;
# Object methods.
$dbh = $obj->db_*; # Where * is the name of the db connection.
$sth = $obj->sql_*; # Where * is the name of the sql statement.
$sth = $obj->sql_*(@sql_pieces);
$obj->DBIwarn($what, $doing);
my $rc = $obj->commit;
my $rc = $obj->commit(@db_names);
my $rc = $obj->rollback;
my $rc = $obj->rollback(@db_names);
DESCRIPTION
Ima::DBI attempts to organize and facilitate caching and more efficient use of database
connections and statement handles by storing DBI and SQL information with your class
(instead of as separate objects). This allows you to pass around just one object without
worrying about a trail of DBI handles behind it.
One of the things I always found annoying about writing large programs with DBI was making
sure that I didn't have duplicate database handles open. I was also annoyed by the
somewhat wasteful nature of the prepare/execute/finish route I'd tend to go through in my
subroutines. The new DBI->connect_cached and DBI->prepare_cached helped a lot, but I
still had to throw around global datasource, username and password information.
So, after a while I grew a small library of DBI helper routines and techniques. Ima::DBI
is the culmination of all this, put into a nice(?), clean(?) class to be inherited from.
Why should I use this thing?
Ima::DBI is a little odd, and it's kinda hard to explain. So lemme explain why you'd want
to use this thing...
• Consolidation of all SQL statements and database information
No matter what, embedding one language into another is messy. DBI alleviates this
somewhat, but I've found a tendency to have that scatter the SQL around inside the
Perl code. Ima::DBI allows you to easily group the SQL statements in one place where
they are easier to maintain (especially if one developer is writing the SQL, another
writing the Perl). Alternatively, you can place your SQL statement alongside the code
which uses it. Whatever floats your boat.
Database connection information (data source, username, password, atrributes, etc...)
can also be consolidated together and tracked.
Both the SQL and the connection info are probably going to change a lot, so having
them well organized and easy to find in the code is a Big Help.
• Holds off opening a database connection until necessary.
While Ima::DBI is informed of all your database connections and SQL statements at
compile-time, it will not connect to the database until you actually prepare a
statement on that connection.
This is obviously very good for programs that sometimes never touch the database.
It's also good for code that has lots of possible connections and statements, but
which typically only use a few. Kinda like an autoloader.
• Easy integration of the DBI handles into your class
Ima::DBI causes each database handle to be associated with your class, allowing you to
pull handles from an instance of your object, as well as making many oft-used DBI
methods available directly from your instance.
This gives you a cleaner OO design, since you can now just throw around the object as
usual and it will carry its associated DBI baggage with it.
• Honors taint mode
It always struck me as a design deficiency that tainted SQL statements could be passed
to $sth->prepare(). For example:
# $user is from an untrusted source and is tainted.
$user = get_user_data_from_the_outside_world;
$sth = $dbh->prepare('DELETE FROM Users WHERE User = $user');
Looks innocent enough... but what if $user was the string "1 OR User LIKE '%'". You
just blew away all your users. Hope you have backups.
Ima::DBI turns on the DBI->connect Taint attribute so that all DBI methods (except
execute()) will no longer accept tainted data. See "Taint" in DBI for details.
• Taints returned data
Databases should be like any other system call. It's the scary Outside World, thus it
should be tainted. Simple. Ima::DBI turns on DBI's Taint attribute on each
connection. This feature is overridable by passing your own Taint attribute to set_db
as normal for DBI. See "Taint" in DBI for details.
• Encapsulation of some of the more repetitive bits of everyday DBI usage
I get lazy a lot and I forget to do things I really should, like using bind_cols(), or
rigorous error checking. Ima::DBI does some of this stuff automatically, other times
it just makes it more convenient.
• Encapsulation of DBI's cache system
DBI's automatic handle caching system is relatively new, and some people aren't aware
of its use. Ima::DBI uses it automatically, so you don't have to worry about it. (It
even makes it a bit more efficient)
• Sharing of database and sql information amongst inherited classes
Any SQL statements and connections created by a class are available to its children
via normal method inheritance.
• Guarantees one connection per program.
One program, one database connection (per database user). One program, one prepared
statement handle (per statement, per database user). That's what Ima::DBI enforces.
Extremely handy in persistent environments (servers, daemons, mod_perl, FastCGI,
etc...)
• Encourages use of bind parameters and columns
Bind parameters are safer and more efficient than embedding the column information
straight into the SQL statement. Bind columns are more efficient than normal
fetching. Ima::DBI pretty much requires the usage of the former, and eases the use of
the latter.
Why shouldn't I use this thing.
• It's all about OO
Although it is possible to use Ima::DBI as a stand-alone module as part of a function-
oriented design, its generally not to be used unless integrated into an object-
oriented design.
• Overkill for small programs
• Overkill for programs with only one or two SQL statements
Its up to you whether the trouble of setting up a class and jumping through the
necessary Ima::DBI hoops is worth it for small programs. To me, it takes just as much
time to set up an Ima::DBI subclass as it would to access DBI without it... but then
again I wrote the module. YMMV.
• Overkill for programs that only use their SQL statements once
Ima::DBI's caching might prove to be an unnecessary performance hog if you never use
the same SQL statement twice. Not sure, I haven't looked into it.
USAGE
The basic steps to "DBIing" a class are:
1. Inherit from Ima::DBI
2. Set up and name all your database connections via set_db()
3. Set up and name all your SQL statements via set_sql()
4. Use sql_* to retrieve your statement handles ($sth) as needed and db_* to retrieve
database handles ($dbh).
Have a look at EXAMPLE below.
TAINTING
Ima::DBI, by default, uses DBI's Taint flag on all connections.
This means that Ima::DBI methods do not accept tainted data, and that all data fetched
from the database will be tainted. This may be different from the DBI behavior you're
used to. See "Taint" in DBI for details.
Class Methods
set_db
Foo->set_db($db_name, $data_source, $user, $password);
Foo->set_db($db_name, $data_source, $user, $password, \%attr);
This method is used in place of DBI->connect to create your database handles. It sets up a
new DBI database handle associated to $db_name. All other arguments are passed through to
DBI->connect_cached.
A new method is created for each db you setup. This new method is called "db_$db_name"...
so, for example, Foo->set_db("foo", ...) will create a method called "db_foo()". (Spaces
in $db_name will be translated into underscores: '_')
%attr is combined with a set of defaults (RaiseError => 1, AutoCommit => 0, PrintError =>
0, Taint => 1). This is a better default IMHO, however it does give databases without
transactions (such as MySQL when used with the default MyISAM table type) a hard time. Be
sure to turn AutoCommit back on if your database does not support transactions.
The actual database handle creation (and thus the database connection) is held off until a
prepare is attempted with this handle.
set_sql
Foo->set_sql($sql_name, $statement, $db_name);
Foo->set_sql($sql_name, $statement, $db_name, $cache);
This method is used in place of DBI->prepare to create your statement handles. It sets up
a new statement handle associated to $sql_name using the database connection associated
with $db_name. $statement is passed through to either DBI->prepare or DBI->prepare_cached
(depending on $cache) to create the statement handle.
If $cache is true or isn't given, then prepare_cached() will be used to prepare the
statement handle and it will be cached. If $cache is false then a normal prepare() will
be used and the statement handle will be recompiled on every sql_*() call. If you have a
statement which changes a lot or is used very infrequently you might not want it cached.
A new method is created for each statement you set up. This new method is
"sql_$sql_name"... so, as with set_db(), Foo->set_sql("bar", ..., "foo"); will create a
method called "sql_bar()" which uses the database connection from "db_foo()". Again,
spaces in $sql_name will be translated into underscores ('_').
The actual statement handle creation is held off until sql_* is first called on this name.
transform_sql
To make up for the limitations of bind parameters, $statement can contain sprintf() style
formatting (ie. %s and such) to allow dynamically generated SQL statements (so to get a
real percent sign, use '%%').
The translation of the SQL happens in transform_sql(), which can be overridden to do more
complex transformations. See Class::DBI for an example.
db_names / db_handles
my @database_names = Foo->db_names;
my @database_handles = Foo->db_handles;
my @database_handles = Foo->db_handles(@db_names);
Returns a list of the database handles set up for this class using set_db(). This
includes all inherited handles.
db_names() simply returns the name of the handle, from which it is possible to access it
by converting it to a method name and calling that db method...
my @db_names = Foo->db_names;
my $db_meth = 'db_'.$db_names[0];
my $dbh = $foo->$db_meth;
Icky, eh? Fortunately, db_handles() does this for you and returns a list of database
handles in the same order as db_names(). Use this sparingly as it will connect you to the
database if you weren't already connected.
If given @db_names, db_handles() will return only the handles for those connections.
These both work as either class or object methods.
sql_names
my @statement_names = Foo->sql_names;
Similar to db_names() this returns the names of all SQL statements set up for this class
using set_sql(), inherited or otherwise.
There is no corresponding sql_handles() because we can't know what arguments to pass in.
Object Methods
db_*
$dbh = $obj->db_*;
This is how you directly access a database handle you set up with set_db.
The actual particular method name is derived from what you told set_db.
db_* will handle all the issues of making sure you're already connected to the database.
sql_*
$sth = $obj->sql_*;
$sth = $obj->sql_*(@sql_pieces);
sql_*() is a catch-all name for the methods you set up with set_sql(). For instance, if
you did:
Foo->set_sql('GetAllFoo', 'Select * From Foo', 'SomeDb');
you'd run that statement with sql_GetAllFoo().
sql_* will handle all the issues of making sure the database is already connected, and the
statement handle is prepared. It returns a prepared statement handle for you to use.
(You're expected to execute() it)
If sql_*() is given a list of @sql_pieces it will use them to fill in your statement,
assuming you have sprintf() formatting tags in your statement. For example:
Foo->set_sql('GetTable', 'Select * From %s', 'Things');
# Assuming we have created an object... this will prepare the
# statement 'Select * From Bar'
$sth = $obj->sql_Search('Bar');
Be very careful with what you feed this function. It cannot do any quoting or escaping
for you, so it is totally up to you to take care of that. Fortunately if you have
tainting on you will be spared the worst.
It is recommended you only use this in cases where bind parameters will not work.
DBIwarn
$obj->DBIwarn($what, $doing);
Produces a useful error for exceptions with DBI.
I'm not particularly happy with this interface
Most useful like this:
eval {
$self->sql_Something->execute($self->{ID}, @stuff);
};
if($@) {
$self->DBIwarn($self->{ID}, 'Something');
return;
}
Modified database handle methods
Ima::DBI makes some of the methods available to your object that are normally only
available via the database handle. In addition, it spices up the API a bit.
commit
$rc = $obj->commit;
$rc = $obj->commit(@db_names);
Derived from $dbh->commit() and basically does the same thing.
If called with no arguments, it causes commit() to be called on all database handles
associated with $obj. Otherwise it commits all database handles whose names are listed in
@db_names.
Alternatively, you may like to do: $rc = $obj->db_Name->commit;
If all the commits succeeded it returns true, false otherwise.
rollback
$rc = $obj->rollback;
$rc = $obj->rollback(@db_names);
Derived from $dbh->rollback, this acts just like Ima::DBI->commit, except that it calls
rollback().
Alternatively, you may like to do: $rc = $obj->db_Name->rollback;
If all the rollbacks succeeded it returns true, false otherwise.
EXAMPLE
package Foo;
use base qw(Ima::DBI);
# Set up database connections (but don't connect yet)
Foo->set_db('Users', 'dbi:Oracle:Foo', 'admin', 'passwd');
Foo->set_db('Customers', 'dbi:Oracle:Foo', 'Staff', 'passwd');
# Set up SQL statements to be used through out the program.
Foo->set_sql('FindUser', <<"SQL", 'Users');
SELECT *
FROM Users
WHERE Name LIKE ?
SQL
Foo->set_sql('ChangeLanguage', <<"SQL", 'Customers');
UPDATE Customers
SET Language = ?
WHERE Country = ?
SQL
# rest of the class as usual.
package main;
$obj = Foo->new;
eval {
# Does connect & prepare
my $sth = $obj->sql_FindUser;
# bind_params, execute & bind_columns
$sth->execute(['Likmi%'], [\($name)]);
while( $sth->fetch ) {
print $name;
}
# Uses cached database and statement handles
$sth = $obj->sql_FindUser;
# bind_params & execute.
$sth->execute('%Hock');
@names = $sth->fetchall;
# connects, prepares
$rows_altered = $obj->sql_ChangeLanguage->execute(qw(es_MX mx));
};
unless ($@) {
# Everything went okay, commit the changes to the customers.
$obj->commit('Customers');
}
else {
$obj->rollback('Customers');
warn "DBI failure: $@";
}
USE WITH MOD_PERL, FASTCGI, ETC.
To help with use in forking environments, Ima::DBI database handles keep track of the PID
of the process they were openend under. If they notice a change (because you forked a new
process), a new handle will be opened in the new process. This prevents a common problem
seen in environments like mod_perl where people would open a handle in the parent process
and then run into trouble when they try to use it from a child process.
Because Ima::DBI handles keeping database connections persistent and prevents problems
with handles openend before forking, it is not necessary to use Apache::DBI when using
Ima::DBI. However, there is one feature of Apache::DBI which you will need in a mod_perl
or FastCGI environment, and that's the automatic rollback it does at the end of each
request. This rollback provides safety from transactions left hanging when some perl code
dies -- a serious problem which could grind your database to a halt with stale locks.
To replace this feature on your own under mod_perl, you can add something like this in a
handler at any phase of the request:
$r->push_handlers(PerlCleanupHandler => sub {
MyImaDBI->rollback();
});
Here "MyImaDBI" is your subclass of Ima::DBI. You could also make this into an actual
module and set the PerlCleanupHandler from your httpd.conf. A similar approach should
work in any long-running environment which has a hook for running some code at the end of
each request.
TODO, Caveat, BUGS, etc....
I seriously doubt that it's thread safe.
You can bet cupcackes to sno-cones that much havoc will be wrought if Ima::DBI is used
in a threaded Perl.
Should make use of private_* handle method to store information
The docs stink.
The docs were originally written when I didn't have a good handle on the module and
how it will be used in practical cases. I need to rewrite the docs from the ground
up.
Need to add debugging hooks.
The thing which immediately comes to mind is a Verbose flag to print out SQL
statements as they are made as well as mention when database connections are made,
etc...
MAINTAINERS
Tony Bowden <tony@tmtm.com> and Perrin Harkins <perrin@elem.com>
ORIGINAL AUTHOR
Michael G Schwern <schwern@pobox.com>
LICENSE
This module is free software. You may distribute under the same terms as Perl itself. IT
COMES WITHOUT WARRANTY OF ANY KIND.
THANKS MUCHLY
Tim Bunce, for enduring many DBI questions and adding Taint, prepare_cached and
connect_cached methods to DBI, simplifying this greatly!
Arena Networks, for effectively paying for Mike to write most of this module.
SEE ALSO
DBI.
You may also choose to check out Class::DBI which hides most of this from view.