=head1 NAME

Tangram::Type - mapping individual fields

=head1 DESCRIPTION

Tangram's persistent type system is extensible, allowing you to mount
your own types and make them persistent. All you have to do is to
register your type and provide mapping code. See L<Tangram::Type::Extending>.

Tangram comes with built-in support for the following types:

=over

=item B<Simple Scalar types>

Supported are strings, integers, real numbers and dates.  More types
of this ilk are easily added.

C<string>, C<int>, C<real>: see L<Tangram::Type::Scalar>

C<date>, C<time>, C<datetime>, C<dmdatetime>: see L<Tangram::Type/Date/Type/Date/DateTime>

=item B<Compound Structure types>

C<perl_dump>: see L<Tangram::Type::Dump::Perl>.  A C<perl_dump> structure may
contain any structure which Data::Dumper can dump successfully.

C<storable>: see L<Tangram::Type::Dump::Storable>.  Very much like C<perl_dump>,
but implemented via the `Storable' serialisation engine.

C<yaml>: see L<Tangram::Type::Dump::YAML>.  Very much like C<perl_dump>, but
implemented via the `YAML' serialisation engine.  Doesn't currently
work, due to inadequacies in the current Perl YAML implementation.

B<NEW in Tangram 2.08>:

C<idbif>: see L<Tangram::Type::Dump::Any>.  Like the above, but can combine
multiple object properties into a single database column.

=item B<`Flat' Array & Hash types>

Note: these are only actually required if you need to be able to query
on individual fields inside the array/hash - otherwise, the
C<perl_dump> or C<idbif> mapping is a lot faster and more flexible.

C<flat_array>: see L<Tangram::Type/Array/Scalar>

C<flat_hash>: see L<Tangram::Type/Hash/Scalar>

=item B<References to other objects>

C<ref>: see L<Tangram::Type::Ref::FromMany> (implementing an B<N to 1> relationship,
in which any object can be the referant)

=item B<Sets of other objects>

Set relationships are closest to the main type of relationship used in
an RDBMS.  Avid CompSci students will know that the relational
database model is based heavily on `Set Theory', which is a subset of
a more general concept of `Categories' - generic couplings of a number
of classes.

In Perl space, these collections are represented via the Set::Object
module.  Sets may not have duplicate elements, and cannot contain
I<undef> values.

C<set>: see L<Tangram::Type::Set::FromMany> (implementing an I<unordered> B<N to N>
relationship, with all objects sharing a common base class)

C<iset>: see L<Tangram::Type::Set::FromOne> (implementing an I<unordered> B<1 to
N> relationship, with all objects sharing a common base class)

=item B<Arrays of other objects>

The addition to Sets, you can have `Arrays' of objects, represented by
a standard Perl array in memory.  Arrays may contain I<undef> values
(in the middle of the list), and the C<array> type may contain
duplicates (ie, the same element present in seperate places in the
list).

C<array> : see L<Tangram::Type::Array::FromMany> (implementing an I<ordered> B<N to N>
relationship, with all objects sharing a common base class)

C<iarray>: see L<Tangram::Type::Array::FromOne> (implementing an I<ordered> B<1
to N> relationship, with all objects sharing a common base class)

=item B<Hashes of other objects>

Much like the Array types, the Hash types are indexed via a string
value, and represented as a Perl hash in memory.  These hashes may not
contain I<undef> values (those are dropped).  The C<hash> type may
contain duplicate elements.

C<hash> : see L<Tangram::Type::Hash::FromMany> (implementing a I<keyed> B<N to N>
relationship, with all objects sharing a common base class)

C<ihash>: see L<Tangram::Type::Hash::FromOne> (implementing a I<keyed> B<1 to N>
relationship, with all objects sharing a common base class)

=back