=head1 NAME

Tangram - Store pure objects in standard relational databases

=head1 SYNOPSIS

See L<Tangram::Tour>

=head1 DESCRIPTION

Tangram is an I<object-relational mapper>.  It is I<orthogonal>,
meaning that it does not require anything of the objects stored in it
(other than the common convention that base objects be based upon
HASHes; individual columns can be anything).

It consists of a I<schema language> that can describe or be built
around an object structure, or so as to closely match an existing SQL
schema (with some limitations).  This schema language is rich enough
to express such common RDBMS features as links, foreign keys, and link
tables.

It also consists of a I<relational database storage> engine, which
based on the schema structure, will make Perl structures persist in a
relational (SQL compliant) database.  References to other objects (or
collections, as represented with foreign keys and link tables) may be
loaded using I<on demand references> that `lazily' load data when it
is needed.

As of Tangram 2.08, the schema need not describe every single object
property, so that you can map only the columns you intend to query.
The rest of the object is then stored in a column via a serialiser,
like L<Data::Dumper>, L<YAML> or L<Storable>.  These structures
themselves may contain arbitrary references to other objects in
storage.

Tangram has soundly engineered transaction support, without
sacrificing excellent data caching abilities.  The general
optimisation strategy of the code makes it most suited for OLTP (aka
application servers) and other situations where it is better to select
and update whole rows than to worry about which columns to
retrieve/update or not retrieve/update.

Once your object are persistent, you can build query expressions to
find them in terms of the schema language that you used to put them
in.  Therefore, the schema data structure does not describe a data
structure, it describes a I<data access pattern>.

If you are not picky about which accessor module to use, preferring to
specify the schema once only, then you can use the seperately
distributed L<Class::Tangram::Generator> to make a set of classes from
a Tangram schema structure.

If you are looking for a tool that implements I<SQL abstraction> only,
you have probably missed the point (of this module, anyway), and a
well-supported module like L<Class::DBI>, or an interactive SQL
modeller like L<Alzabo> will likely suit your needs better.

Tangram is beginning to include preliminary support for aggregation
functions, and currently supports grouping, summing and counting.
Joins must currently be in terms of integer primary key columns, to
extend past this would require extra mapping types to be developed.
Basic support for alternative join types is present, but in its
infancy.

Tangram currently contains no support for database-side updates (ie,
C<UPDATE foo SET bar = 'baz' where frop = 'blarg'>), but support is
planned.

There is no support for creating views based on existing classes to
make new derived classes; you have to use your database SQL and create
corresponding Tangram classes manually to do that.

Tangram has a web site at L<http://tangram.utsl.gen.nz/>, currently
sponsored by MarketView (New Zealand) Ltd.

=head1 DOCUMENTATION INDEX

=head1 CONTENTS

=over

=item L<Tangram::Tour>

The original "Guided Tour" of the features of Tangram, by Jean-Louis
Leroy.

=item L<Tangram::Intro>

The humble beginnings of a new guided tour, based on the
next-generation features found in Tangram 2.08.

=item L<Tangram::Springfield>

The classes and schema used in the Guided Tour(s).

=item L<Tangram::Storage>

The main database handle class.  Includes details on query syntax.

=item L<Tangram::Cursor>

Return an iterator that retrieves persistent objects in a result set
one by one.

=item L<Tangram::Schema>

The Tangram schema structure - representing your data model so that
Tangram can map it.

=item L<Tangram::Relational::Mappings>

An informative text on exactly how Object Relational Mapping is
accomplished by the Tangram::Relational back-end, what the different
styles of mapping are, and how each is selected.

=item L<Tangram::Type>

What Tangram types are available.  This page is an index of other
manual pages that express the data and relationship types available in
Tangram.

=item L<Tangram::Type::Extending>

How to write your own custom types for Tangram.

=item L<Tangram::Dialect>

Database-specific extensions to Tangram, such as L<Tangram::mysql> and
L<Tangram::Sybase>.  These extensions only add functionality, and are
not required for core operation of Tangram.

=head1 COMPATIBILITY

Tangram has been known to run in the following environments, however,
Tangram uses standard SQL and should be usable with any SQL-83
compliant database.  Most of the requirements are simply avoiding the
worst bugs.

Note that some functions (e.g. transactions and subselects) may not be
available in some environments. This is reported during the test
suite.

=over 4

=item *

Perl 5.005_03+, 5.6.1+, 5.8.1+ (5.8.0 had a nasty bug and doesn't work
with Tangram)

=item *

Set::Object 1.04 (though the latest version is highly recommended)

=item *

DBI 1.14

=item *

DBD::mysql 2.0402

=item *

DBD::Oracle 1.06

=item *

DBD::Sybase 0.21

=item *

DBD::SQLite 1.07

=item *

DBD::Pg 0.93

=back

=head1 LICENSE & WARRANTY

You may use Tangram, free of charge, under the terms of the GPL.  This
notice applies to the entire distribution and all of its parts.

You can obtain a commercial license for old (2.04 and earlier)
versions of Tangram from Sound Object Logic, see
http://www.soundobjectlogic.com/tangram/licenses.html.

TANGRAM COMES WITHOUT ANY WARRANTY OF ANY KIND.  IT DOES NOT EVEN COME
WITH ANY KIND OF VAGUE IMPLICATION THAT IT DOES ANYTHING MORE THAN
GIVE YOUR COMPUTER HINTS ABOUT HOW TO TRY STIRRING ITS ELECTRONS.  THE
AUTHORS ARE NOT RESPONSIBLE FOR THE RESULTANT ELECTRON CONFIGURATION
IN ANY WAY INCLUDING TRANSMUTATIONS OF ELECTRONS INTO OTHER FIELDS
SUCH AS MAGNETIC MEDIA OR PUNCH CARDS.

=head1 SUPPORT

Please send bug reports directly to the Tangram 2 maintainer's mailing
list <t2-users@lists.utsl.gen.nz>, and please CC:
<bug-Tangram@rt.cpan.org> so your fault can be tracked accurately.

Whenever possible, include a short yet complete script demonstrating
the problem.  (read: if you want it fixed quicker, demonstrate it)

Questions of general interest should should be posted to the mailing
list, but not sent to rt.cpan.org.

=head1 AUTHORS

All the code and documentation for versions 2.04 and earlier, as well
as some changes in the 2.05 release, were written by Jean-Louis Leroy
(jll@soundobjectlogic.com) and Sound Object Logic.

Sam Vilain <sam@vilain.net> is the author of the derived work that is
Tangram 2.05 and later.

Andres Kievsky <ank@cpan.org> has contributed to the Tangram code
starting with Tangram 2.08.

=cut