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 seperate 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 persistant
        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 unecessary 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 ($sth) as needed and
        db_* to retreive database handles ($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.

