package DBIx::Hash2Table;

use strict;
use warnings;

use Carp;

our $VERSION = '2.05';

# -----------------------------------------------

# Preloaded methods go here.

# -----------------------------------------------

# Encapsulated class data.

{
	my(%_attr_data) =
	(
		_columns	=> '',
		_dbh		=> '',
		_extras		=> [],
		_hash_ref	=> '',
		_table_name	=> '',
	);

	sub _default_for
	{
		my($self, $attr_name) = @_;

		$_attr_data{$attr_name};
	}

	sub _save
	{
		my($self, $sth, $hash_ref, $parent) = @_;

		my(@bind);

		for my $key (keys %$hash_ref)
		{
			# If we have a hash ref, which we almost always do have...

			if (ref($$hash_ref{$key}) eq 'HASH')
			{
				$$self{'_id'}++;

				@bind = ($$self{'_id'}, $parent, $key);

				for (@{$$self{'_extras'} })
				{
					push(@bind, exists($$hash_ref{$key}{$_}) ? $$hash_ref{$key}{$_} : undef);
				}

				$sth -> execute(@bind);

				# Curse again. (Aka 'recurse', for non-native speakers of English.)

				$self -> _save($sth, $$hash_ref{$key}, $$self{'_id'});
			}
		}

	}	# End of _save.

	sub _standard_keys
	{
		keys %_attr_data;
	}
}

# -----------------------------------------------

sub insert
{
	my($self)			= @_;
	$$self{'_extras'}	= [sort @{$$self{'_extras'} }];
	my($sql)			= "insert into $$self{'_table_name'} (" . join(', ', @{$$self{'_columns'} }, @{$$self{'_extras'} }) . ') values (' . join(', ', ('?') x ($#{$$self{'_columns'} } + $#{$$self{'_extras'} } + 2) ) . ')';
	my($sth)			= $$self{'_dbh'} -> prepare($sql);
	$$self{'_id'}		= 0;

	$self -> _save($sth, $$self{'_hash_ref'}, 0);

}	# End of insert.

# -----------------------------------------------

sub new
{
	my($class, %arg)	= @_;
	my($self)			= bless({}, $class);

	for my $attr_name ($self -> _standard_keys() )
	{
		my($arg_name) = $attr_name =~ /^_(.*)/;

		if (exists($arg{$arg_name}) )
		{
			$$self{$attr_name} = $arg{$arg_name};
		}
		else
		{
			$$self{$attr_name} = $self -> _default_for($attr_name);
		}
	}

	croak(__PACKAGE__ . ". You must supply a value for each parameter except 'extras'")
		if (! ($$self{'_columns'} && $$self{'_dbh'} && $$self{'_hash_ref'} && $$self{'_table_name'}) );

	return $self;

}	# End of new.

# -----------------------------------------------

1;

__END__

=head1 NAME

C<DBIx::Hash2Table> - Save a hash into a database table

=head1 Synopsis

	#!/usr/bin/perl

	my(%entity)     = create_a_hash(...);
	my($dbh)        = DBI -> connect(...);
	my($table_name) = 'entity';

	# Cope with MySQL-specific SQL.
	eval{$dbh -> do("drop table if exists $table_name")};

	# Cope with non-existant table.
	eval{$dbh -> do("drop table $table_name")};

	my($sql) = "create table $table_name (id int, parent_id int, " .
				"code char(5), name varchar(255), _url varchar(255) )";

	$dbh -> do($sql);

	DBIx::Hash2Table -> new
	(
		hash_ref   => \%entity,
		dbh        => $dbh,
		table_name => $table_name,
		columns    => ['id', 'parent_id', 'name'],
#		extras     => ['code']
#		extras     => ['_url', 'code']
#		extras     => ['code', '_url']
	) -> insert();

=head1 Description

C<DBIx::Hash2Table> is a pure Perl module.

This module saves a hash ref into an existing database table of at least 3 columns.

Each row in the table will consist of these 3 columns, at least: id (row number),
parent's id, and the value of a hash key.

You specify the names of these 3 columns in the constructor's array ref parameter
called C<columns>.

I suggest you display the script examples/test-hash2table.pl in another window while
reading the following.

In fact, you are I<strongly> recommended to run the demo now, and examine the resultant
database table, before reading further. Then, remove the comment '#' from one of lines
84 .. 86 and run it again.

In the hash ref being saved to the database, hash keys normally point to hash refs.
This nested structure is preserved when the data is written to the table.

That is, the hash keys which point to hash refs become parents in the database,
and keys within the hash ref being pointed to may become children of this parent.

I say 'may' because inside the hash ref you can have hash keys which are column names,
and you can have hash keys which are just 'normal' hash keys, ie not column names.

If the nested hash key is a column name, then it should point to a non-ref, ie a number
or a string. In that case, you can optionally have the value it points to written to the
table.

You activate this feature by putting the names of the columns you wish to have saved in
the database into the constructor's array ref parameter called C<extras>.

In the example code, such a nested hash keys are called code, _run_mode and _url, and at
lines 84 .. 86 you can control whether or not any or all of these values are written to
the table.

If the nested hash key is not a column name, then it should point to a hash ref, and when
its turn comes, it too will be written to the table.

In more detail, the 3 mandatory columns in each row of the database are:

=over 4

=item *

An id column

This column is for the (unique) id of the row containing the hash key.

You do not have to define this column of the table to be unique, or to be a database key,
but that might be a Good Idea.

C<DBIx::Hash2Table> counts an integer up from 1, to generate the values for this column.

=item *

The parent's id column

This column is for the id of the row of the parent of the hash key.

The root key(s) of the hash will have a parent id of 0.

=item *

A name column

This column is for the value of the hash key itself.

=back

=head1 Distributions

This module is available both as a Unix-style distro (*.tgz) and an
ActiveState-style distro (*.ppd). The latter is shipped in a *.zip file.

See http://savage.net.au/Perl-modules.html for details.

See http://savage.net.au/Perl-modules/html/installing-a-module.html for
help on unpacking and installing each type of distro.

=head1 Constructor and initialization

new(...) returns a C<DBIx::Hash2Table> object.

This is the class's contructor.

Parameters:

=over 4

=item *

hash_ref

A reference to the hash to be inserted in a database table.

This parameter is mandatory.

=item *

dbh

A database handle.

This parameter is mandatory.

=item *

table_name

This is the name of the table to populate.

This parameter is mandatory.

=item *

columns

This is an array ref of the 3 mandatory column names.

Warning: The order of entries in this array ref is of great significance. Of course, just
because the column names must be in this order does not mean the table itself must be
declared with the columns in the same order.

=over 4

=item *

Index 0

This is the column name used for the id column.

Ids start at 1.

=item *

Index 1

This is the column name used for the id of the parent of the hash key.

The root key(s) of the hash will have a parent id of 0.

=item *

Index 2

This is the column name used for the hash key itself.

=back

This parameter is mandatory.

=item *

extras

This is an array ref of column names which are also keys in the hash ref.

It defaults to [].

This parameter is optional.

These column names which are hash keys have the following properties:

=over 4

=item *

It's a child

The hash key is a child of the 'current' hash key.

=item *

It's value is not a reference

The value pointed to be this hash key is a non-ref, ie it's just a number or a string.

=item *

Save me!

You want the hash key's value to be written to the 'current' row of the table.

In other words, even though this hash key (which is a column name!) is a child of the
'current' hash key, the value pointed to by this hash key is written to the same row
has the 'current' hash key.

=back

The program examples/test-hash2table.pl shows exactly what this means.

=back

=head1 Method: new(...)

Returns an object of type C<DBIx::Hash2Table>.

See above, in the section called 'Constructor and initialization'.

=head1 Method: insert()

Returns nothing.

Calling insert() actually executes the SQL insert statement, and recursively writes
all hash keys to the table.

=head1 FAQ

Q: What is the point of this module?

A: To be able to save a hash to permanent storage via a database rather than via a file.

Q: Can your other module C<DBIx::Table2Hash> reconstruct a hash written by this module?

A: No. Sorry. Perhaps one day.

=head1 Repository

L<https://github.com/ronsavage/DBIx-Hash2Table>

=head1 Support

Bugs should be reported via the CPAN bug tracker at

L<https://github.com/ronsavage/DBIx-Hash2Table/issues>

=head1 Author

C<DBIx::Hash2Table> was written by Ron Savage I<E<lt>ron@savage.net.auE<gt>> in 2003.

Home page: L<http://savage.net.au/index.html>

=head1 Copyright

Australian copyright (c) 2003, Ron Savage.
	All Programs of mine are 'OSI Certified Open Source Software';
	you can redistribute them and/or modify them under the terms of
	The Artistic License, a copy of which is available at:
	http://www.opensource.org/licenses/index.html

=cut