
# to be completed.

=head1 NAME

Tangram::Intro - an introduction to Tangram

=head1 SYNOPSIS

 # http://www.faqs.org/rfcs/rfc2324.html
 perl -MNet::HTCPCP -le 'Net::HTCPCP->new("BREW")->send'

 perldoc Tangram::Intro

=head1 YIN AND YANG OF OBJECT PERSISTENCE

There are yin and yang approaches to object persistence.  Are you a
yin programmer or a yang programmer?

=over *

=item B<yin>

(without, empty) - "I just want to store my objects"

=item B<yang>

(with, full) - "I want my database to represent my object structure"

=back

Please skip to the introduction that suits you.

=head2 YIN OBJECT PERSISTENCE (A LA PIXIE)

One yin approach is to have a single table of objects -

  +----+------------------+
  | ID | DATA             |
  +----+------------------+

This is the raw technique used by modules like MLDBM.  Stick objects
in, get a tag (or, insert with a tag), and later present that tag to
get the objects out.

Modules like L<Pixie> extend this concept, to allow you to have
objects that are I<persistent> (ie, have been stored and could be
retrieved again by ID or name), inside other structures that are also
persistent.  This is achieved without storing the same structure
twice, without having to fetch all objects that are in a single
persistent structure, and without requiring that the objects being
stored even know that they are being stored.

Fantastic.  This method is fine for any application that doesn't mind
single threading data manipulation on objects.

Enough banter, let's see some code; here's a project schema:

 package MyProject::Tangram;

 use Heritable::Types;
 use Tangram::Core;
 use Tangram::Type::Dump::Any;

 our $schema =
     Tangram::Schema->new
         ( { classes =>
              [ HASH => {
                    fields => {
                        idbif => # poof!
                           undef
                    },
                },
              ],
           } );

  sub db { Tangram::Storage->new($schema, @_) }

This defines a sort of "store anything" schema.  You could deploy your
database like this:

 my $dbh = DBI->connect
      ("dbi:mysql:tangram", "user", "pass");
 Tangram::Relational->deploy ( $MyProject::Tangram::schema,
                               $dbh );

And then shove objects in and out like this:

  use MyProject::Tangram;
  my $storage = MyProject::Tangram::db
      ("dbi:mysql:tangram", "user", "pass");

  my $object = bless { first_name => "Homer",
		       last_lame => "Simpson",
		      }, "NaturalPerson";
  my $oid = $storage->insert($object);

  my $homer = $storage->load($oid);

If this Pixie-like functionality is all you're after, then you can
stop there, and isn't much slower than Pixie.  You also get the choice
of whether you want to freeze data structures in your database via
"Data::Dumper", "Storable" or "YAML".

=head2 YANG OBJECT PERSISTENCE

If you wish to enable concurrency without paying a large performance
penalty for most standard types of data access, then you may need to
extract single parts of your objects into columns.  That way, you can
make the most use of your database's (hopefully) highly tuned and
refined ability to cache and manipulate data indices.

In that case, you may choose to start with mapping all of your
object's properties to database columns (as was the only option before
Tangram 2.08):

 package MyProject::Tangram;

 use Tangram::Core;

 our $schema =
     Tangram::Schema->new
         ( { classes =>
              [ NaturalPerson => {
                    fields => {
                        string => {
			},
			integer => {
				    }
                    },
                },
              ],
           } );

  sub db { Tangram::Storage->new($schema, @_) }

Tangram has been transaction-savvy since version 1.  So long as you
are careful to flush Tangram's object cache, before you start doing
selects that lock rows for update, then you can easily write
transaction protected programs.

=head1 FURTHER READING

The original L<Tangram::Tour> is still worth reading - but bear in
mind the above - Tangram can map schemas richly or simply, and the
choice is up to you.  See also L<Tangram::Sucks> for the things which
need to be improved.

=cut

