DBI::DBD::SqlEngine::HowTo - phpMan

NAME
    DBI::DBD::SqlEngine::HowTo - Guide to create DBI::DBD::SqlEngine based
    driver

SYNOPSIS
      perldoc DBI::DBD::SqlEngine::HowTo
      perldoc DBI
      perldoc DBI::DBD
      perldoc DBI::DBD::SqlEngine::Developers
      perldoc SQL::Eval
      perldoc DBI::DBD::SqlEngine
      perldoc DBI::DBD::SqlEngine::HowTo
      perldoc SQL::Statement::Embed

DESCRIPTION
    This document provides a step-by-step guide, how to create a new
    "DBI::DBD::SqlEngine" based DBD. It expects that you carefully read the
    DBI documentation and that you're familiar with DBI::DBD and had read
    and understood DBD::ExampleP.

    This document addresses experienced developers who are really sure that
    they need to invest time when writing a new DBI Driver. Writing a DBI
    Driver is neither a weekend project nor an easy job for hobby coders
    after work. Expect one or two man-month of time for the first start.

    Those who are still reading, should be able to sing the rules of
    "CREATING A NEW DRIVER" in DBI::DBD.

CREATING DRIVER CLASSES
    Do you have an entry in DBI's DBD registry? DBI::DBD::SqlEngine expect
    having a unique prefix for every driver class in inheritance chain.

    It's easy to get a prefix - just drop the DBI team a note
    ("GETTING_HELP" in DBI). If you want for some reason hide your work,
    take a look at Class::Method::Modifiers how to wrap a private prefix
    method around existing "driver_prefix".

    For this guide, a prefix of "foo_" is assumed.

  Sample Skeleton
        package DBD::Foo;

        use strict;
        use warnings;
        use vars qw($VERSION);
        use base qw(DBI::DBD::SqlEngine);

        use DBI ();

        $VERSION = "0.001";

        package DBD::Foo::dr;

        use vars qw(@ISA $imp_data_size);

        @ISA = qw(DBI::DBD::SqlEngine::dr);
        $imp_data_size = 0;

        package DBD::Foo::db;

        use vars qw(@ISA $imp_data_size);

        @ISA = qw(DBI::DBD::SqlEngine::db);
        $imp_data_size = 0;

        package DBD::Foo::st;

        use vars qw(@ISA $imp_data_size);

        @ISA = qw(DBI::DBD::SqlEngine::st);
        $imp_data_size = 0;

        package DBD::Foo::Statement;

        use vars qw(@ISA);

        @ISA = qw(DBI::DBD::SqlEngine::Statement);

        package DBD::Foo::Table;

        use vars qw(@ISA);

        @ISA = qw(DBI::DBD::SqlEngine::Table);

        1;

    Tiny, eh? And all you have now is a DBD named foo which will is able to
    deal with temporary tables, as long as you use SQL::Statement. In
    DBI::SQL::Nano environments, this DBD can do nothing.

  Deal with own attributes
    Before we start doing usable stuff with our DBI driver, we need to think
    about what we want to do and how we want to do it.

    Do we need tunable knobs accessible by users? Do we need status
    information? All this is handled in attributes of the database handles
    (be careful when your DBD is running "behind" a DBD::Gofer proxy).

    How come the attributes into the DBD and how are they fetchable by the
    user? Good question, but you should know because you've read the DBI
    documentation.

    "DBI::DBD::SqlEngine::db::FETCH" and "DBI::DBD::SqlEngine::db::STORE"
    taking care for you - all they need to know is which attribute names are
    valid and mutable or immutable. Tell them by adding
    "init_valid_attributes" to your db class:

        sub init_valid_attributes
        {
            my $dbh = $_[0];

            $dbh->SUPER::init_valid_attributes ();

            $dbh->{foo_valid_attrs} = {
                foo_version         => 1,   # contains version of this driver
                foo_valid_attrs     => 1,   # contains the valid attributes of foo drivers
                foo_readonly_attrs  => 1,   # contains immutable attributes of foo drivers
                foo_bar             => 1,   # contains the bar attribute
                foo_baz             => 1,   # contains the baz attribute
                foo_manager         => 1,   # contains the manager of the driver instance
                foo_manager_type    => 1,   # contains the manager class of the driver instance
            };
            $dbh->{foo_readonly_attrs} = {
                foo_version         => 1,   # ensure no-one modifies the driver version
                foo_valid_attrs     => 1,   # do not permit one to add more valid attributes ...
                foo_readonly_attrs  => 1,   # ... or make the immutable mutable
                foo_manager         => 1,   # manager is set internally only
            };

            return $dbh;
        }

    Woooho - but now the user cannot assign new managers? This is intended,
    overwrite "STORE" to handle it!

        sub STORE ($$$)
        {
            my ( $dbh, $attrib, $value ) = @_;

            $dbh->SUPER::STORE( $attrib, $value );

            # we're still alive, so no exception is thrown ...
            # by DBI::DBD::SqlEngine::db::STORE
            if ( $attrib eq "foo_manager_type" )
            {
                $dbh->{foo_manager} = $dbh->{foo_manager_type}->new();
                # ... probably correct some states based on the new
                # foo_manager_type - see DBD::Sys for an example
            }
        }

    But ... my driver runs without a manager until someone first assignes a
    "foo_manager_type". Well, no - there're two places where you can
    initialize defaults:

        sub init_default_attributes
        {
            my ($dbh, $phase) = @_;

            $dbh->SUPER::init_default_attributes($phase);

            if( 0 == $phase )
            {
                # init all attributes which have no knowledge about
                # user settings from DSN or the attribute hash
                $dbh->{foo_manager_type} = "DBD::Foo::Manager";
            }
            elsif( 1 == $phase )
            {
                # init phase with more knowledge from DSN or attribute
                # hash
                $dbh->{foo_manager} = $dbh->{foo_manager_type}->new();
            }

            return $dbh;
        }

    So far we can prevent the users to use our database driver as data
    storage for anything and everything. We care only about the real
    important stuff for peace on earth and alike attributes. But in fact,
    the driver still can't do anything. It can do less than nothing -
    meanwhile it's not a stupid storage area anymore.

  User comfort
    "DBI::DBD::SqlEngine" since 0.05 consolidates all persistent meta data
    of a table into a single structure stored in "$dbh->{sql_meta}". While
    DBI::DBD::SqlEngine provides only readonly access to this structure,
    modifications are still allowed.

    Primarily DBI::DBD::SqlEngine provides access via the setters
    "new_sql_engine_meta", "get_sql_engine_meta", "get_single_table_meta",
    "set_single_table_meta", "set_sql_engine_meta" and
    "clear_sql_engine_meta". Those methods are easily accessible by the
    users via the "$dbh->func ()" interface provided by DBI. Well, many
    users don't feel comfortize when calling

        # don't require extension for tables cars
        $dbh->func ("cars", "f_ext", ".csv", "set_sql_engine_meta");

    DBI::DBD::SqlEngine will inject a method into your driver to increase
    the user comfort to allow:

        # don't require extension for tables cars
        $dbh->foo_set_meta ("cars", "f_ext", ".csv");

    Better, but here and there users likes to do:

        # don't require extension for tables cars
        $dbh->{foo_tables}->{cars}->{f_ext} = ".csv";

    This interface is provided when derived DBD's define following in
    "init_valid_attributes" (re-capture "Deal with own attributes"):

        sub init_valid_attributes
        {
            my $dbh = $_[0];

            $dbh->SUPER::init_valid_attributes ();

            $dbh->{foo_valid_attrs} = {
                foo_version         => 1,   # contains version of this driver
                foo_valid_attrs     => 1,   # contains the valid attributes of foo drivers
                foo_readonly_attrs  => 1,   # contains immutable attributes of foo drivers
                foo_bar             => 1,   # contains the bar attribute
                foo_baz             => 1,   # contains the baz attribute
                foo_manager         => 1,   # contains the manager of the driver instance
                foo_manager_type    => 1,   # contains the manager class of the driver instance
                foo_meta            => 1,   # contains the public interface to modify table meta attributes
            };
            $dbh->{foo_readonly_attrs} = {
                foo_version         => 1,   # ensure no-one modifies the driver version
                foo_valid_attrs     => 1,   # do not permit one to add more valid attributes ...
                foo_readonly_attrs  => 1,   # ... or make the immutable mutable
                foo_manager         => 1,   # manager is set internally only
                foo_meta            => 1,   # ensure public interface to modify table meta attributes are immutable
            };

            $dbh->{foo_meta} = "foo_tables";

            return $dbh;
        }

    This provides a tied hash in "$dbh->{foo_tables}" and a tied hash for
    each table's meta data in "$dbh->{foo_tables}->{$table_name}".
    Modifications on the table meta attributes are done using the table
    methods:

        sub get_table_meta_attr { ... }
        sub set_table_meta_attr { ... }

    Both methods can adjust the attribute name for compatibility reasons,
    e.g. when former versions of the DBD allowed different names to be used
    for the same flag:

        my %compat_map = (
                           abc => 'foo_abc',
                           xyz => 'foo_xyz',
                         );
        __PACKAGE__->register_compat_map( \%compat_map );

    If any user modification on a meta attribute needs reinitialization of
    the meta structure (in case of "DBI::DBD::SqlEngine" these are the
    attributes "f_file", "f_dir", "f_ext" and "f_lockfile"), inform
    DBI::DBD::SqlEngine by doing

        my %reset_on_modify = (
                                foo_xyz => "foo_bar",
                                foo_abc => "foo_bar",
                              );
        __PACKAGE__->register_reset_on_modify( \%reset_on_modify );

    The next access to the table meta data will force DBI::DBD::SqlEngine to
    re-do the entire meta initialization process.

    Any further action which needs to be taken can handled in
    "table_meta_attr_changed":

        sub table_meta_attr_changed
        {
            my ($class, $meta, $attrib, $value) = @_;
            ...
            $class->SUPER::table_meta_attr_changed ($meta, $attrib, $value);
        }

    This is done before the new value is set in $meta, so the attribute
    changed handler can act depending on the old value.

  Dealing with Tables
    Let's put some life into it - it's going to be time for it.

    This is a good point where a quick side step to SQL::Statement::Embed
    will help to shorten the next paragraph. The documentation in
    SQL::Statement::Embed regarding embedding in own DBD's works pretty fine
    with SQL::Statement and DBI::SQL::Nano.

    Second look should go to DBI::DBD::SqlEngine::Developers to get a
    picture over the driver part of the table API. Usually there isn't much
    to do for an easy driver.

  Testing
    Now you should have your first own DBD. Was easy, wasn't it? But does it
    work well? Prove it by writing tests and remember to use
    dbd_edit_mm_attribs from DBI::DBD to ensure testing even rare cases.

AUTHOR
    This guide is written by Jens Rehsack. DBI::DBD::SqlEngine is written by
    Jens Rehsack using code from DBD::File originally written by Jochen
    Wiedmann and Jeff Zucker.

    The module DBI::DBD::SqlEngine is currently maintained by

    H.Merijn Brand < h.m.brand at xs4all.nl > and Jens Rehsack < rehsack at
    googlemail.com >

COPYRIGHT AND LICENSE
    Copyright (C) 2010 by H.Merijn Brand & Jens Rehsack

    All rights reserved.

    You may freely distribute and/or modify this module under the terms of
    either the GNU General Public License (GPL) or the Artistic License, as
    specified in the Perl README file.