=head1 NAME

Class::AutoDB::Collection - Schema information for one collection

=head1 SYNOPSIS

This is a helper class for Class::AutoDB::Registry which represents the
schema information for one collection.

 use Class::AutoDB::Registration;
 use Class::AutoDB::Collection;
 my $registration=new Class::AutoDB::Registration
   (-class=>'Person',
    -collection=>'Person',
    -keys=>qq(name string, dob integer, significant_other object, 
              friends list(object)),
    -transients=>[qw(age)],
    -auto_gets=>[qw(significant_other)]);
 
 my $collection=new Class::AutoDB::Collection
   (-name=>'Person',-register=>$registration);
 
 # Get the object's attributes
 my $name=$collection->name; 
 my $keys=$collection->keys;            # hash of key=>type pairs
 my $tables=$collection->tables;        # Class::AutoDB::Table objects 
                                        #   that implement this collection 
 
 my @sql=$collection->schema;           # SQL statements to create collection
 my @sql=$collection->schema('create'); # same as above
 my @sql=$collection->schema('drop');   # SQL statements to drop collection
 my @sql=$collection->schema('alter',$diff); 
                                        # SQL statements to alter collection
                                        #   ($diff is CollectionDiff object)

=head1 DESCRIPTION

This class represents processed registration information for one
collection. Registrations are fed into the class via the 'register'
method which combines the information to obtain a single hash of
key=E<gt>type pairs. It makes sure that if the same key is registered
multiple times, it has the same type each time. It further processes
the information to determine the database tables needed to implement
the collection, and the SQL statements needed to create, and drop those
tables. It also has the ability to compare its current state to a
Class::AutoDB::CollectionDiff object and generate the SQL statements
needed to alter the current schema the new one.

This class I<does not talk to the database>.
 
=cut