NAME

XML::Generator::PerlData - Perl extension for generating SAX2 events from nested Perl data structures.

SYNOPSIS

use XML::Generator::PerlData;
use SomeSAX2HandlerOrFilter;

## Simple style ##

# get a deeply nested Perl data structure...
my $hash_ref = $obj->getScaryNestedDataStructure();

# create an instance of a handler class to forward events to...
my $handler = SomeSAX2HandlerOrFilter->new();

# create an instance of the PerlData driver...
my $driver  = XML::Generator::PerlData->new( Handler => $handler );

# generate XML from the data structure...
$driver->parse( $hash_ref );


## Or, Stream style ##

use XML::Generator::PerlData;
use SomeSAX2HandlerOrFilter;

# create an instance of a handler class to forward events to...
my $handler = SomeSAX2HandlerOrFilter->new();

# create an instance of the PerlData driver...
my $driver  = XML::Generator::PerlData->new( Handler => $handler );

# start the event stream...
$driver->parse_start();

# pass the data through in chunks
# (from a database handle here)
while ( my $array_ref = $dbd_sth->fetchrow_arrayref ) {
    $driver->parse_chunk( $array_ref );
}

# end the event stream...
$driver->parse_end();

and you're done...

DESCRIPTION

XML::Generator::PerlData provides a simple way to generate SAX2 events from nested Perl data structures, while providing finer-grained control over the resulting document streams.

Processing comes in two flavors: Simple Style and Stream Style:

In a nutshell, 'simple style' is best used for those cases where you have a a single Perl data structure that you want to convert to XML as quickly and painlessly as possible. 'Stream style' is more useful for cases where you are receiving chunks of data (like from a DBI handle) and you want to process those chunks as they appear. See PROCESSING METHODS for more info about how each style works.

CONSTRUCTOR METHOD AND CONFIGURATION OPTIONS

new (class constructor)

Accepts: An optional hash of configuration options.

Returns: A new instance of the XML::Generator::PerlData class.

Creates a new instance of XML::Generator::PerlData.

While basic usage of this module is designed to be simple and straightforward, there is a small host of options available to help ensure that the SAX event streams (and by extension the XML documents) that are created from the data structures you pass are in just the format that you want.

OPTIONS

• Handler (required)

  XML::Generator::PerlData is a SAX Driver/Generator. As such, it needs a SAX Handler or Filter class to forward its events to. The value for this option must be an instance of a SAX2-aware Handler or Filter.

• rootname (optional)

  Sets the name of the top-level (root) element. The default is 'document'.

• defaultname (optional)

  Sets the default name to be used for elements when no other logical name is available (think lists-of-lists). The default is 'default'.

• keymap (optional)

  Often, the names of the keys in a given hash do not map directly to the XML elements names that you want to appear in the resulting document. The option contains a set of keyname->element name mappings for the current process.

• skipelements (optional)

  Passed in as an array reference, this option sets the internal list of keynames that will be skipped over during processing. Note that any descendant structures belonging to those keys will also be skipped.

• attrmap (optional)

  Used to determine which 'children' of a given hash key/element-name will be forwarded as attributes of that element rather than as child elements.

  (see CAVEATS for a discussion of the limitations of this method.)

• namespaces (optional)

  Sets the internal list of namespace/prefix pairs for the current process. It takes the form of a hash, where the keys are the URIs of the given namespace and the values are the associated prefix.

  To set a default (unprefixed) namespace, set the prefix to '#default'.

• namespacemap (optional)

  Sets which elements in the result will be bound to which declared namespaces. It takes the form of a hash of key/value pairs where the keys are one of the declared namespace URIs that are relevant to the current process and the values are either single key/element names or an array reference of key/element names.

• skiproot (optional)

  When set to a defined value, this option blocks the generator from adding the top-level root element when parse() or start_stream() and end_stream() are called.

  Do not use this option unless you absolutely sure you know what you are doing and why, since the resulting event stream will most likely produce non-well-formed XML.

• bindattrs (optional)

  When set to a defined value, this option tells the generator to bind attributes to the same namespace as element that contains them. By default attributes will be unbound and unprefixed.

PROCESSING METHODS

SIMPLE STYLE PROCESSING

parse

Accepts: A reference to a Perl data structure. Optionally, a hash of config options.

Returns: [none]

The core method used during 'simple style' processing, this method accepts a reference to a Perl data structure and, based on the options passed, produces a stream of SAX events that can be used to transform that structure into XML. The optional second argument is a hash of config options identical to those detailed in the OPTIONS section of the the new() constructor description.

Examples:

$pd->parse( \%my_hash );

$pd->parse( \%my_hash, rootname => 'recordset' );

$pd->parse( \@my_list, %some_options );

$pd->parse( $my_hashref );

$pd->parse( $my_arrayref, keymap => { default => ['foo', 'bar', 'baz'] } );

STREAM STYLE PROCESSING

parse_start

Accepts: An optional hash of config options.

Returns: [none]

Starts the SAX event stream and (unless configured not to) fires the event the top-level root element. The optional argument is a hash of config options identical to those detailed in the OPTIONS section of the the new() constructor description.

Example:

$pd->start_stream();

parse_end

Accepts: [none].

Returns: Varies. Returns what the final Handler returns.

Ends the SAX event stream and (unless configured not to) fires the event to close the top-level root element.

Example:

$pd->parse_end(); 

parse_chunk

Accepts: A reference to a Perl data structure.

Returns: [none]

The core method used during 'stream style' processing, this method accepts a reference to a Perl data structure and, based on the options passed, produces a stream of SAX events that can be used to transform that structure into XML.

Examples:

$pd->parse_chunk( \%my_hash );

$pd->parse_chunk( \@my_list );

$pd->parse_chunk( $my_hashref );

$pd->parse_chunk( $my_arrayref );

CONFIGURATION METHODS

All config options can be passed to calls to the new() constructor using the typical "hash of named properties" syntax. The methods below offer direct access to the individual options (or ways to add/remove the smaller definitions contained by those options).

init

Accepts: The same configuration options that can be passed to the new() constructor.

Returns: [none]

See the list of OPTIONS above in the definition of new() for details.

rootname

Accepts: A string or [none].

Returns: The current root name.

When called with an argument, this method sets the name of the top-level (root) element. It always returns the name of the current (or new) root name.

Examples:

$pd->rootname( $new_name );   

my $current_root = $pd->rootname();   

defaultname

Accepts: A string or [none]

Returns: The current default element name.

When called with an argument, this method sets the name of the default element. It always returns the name of the current (or new) default name.

Examples:

$pd->defaultname( $new_name );   

my $current_default = $pd->defaultname();   

keymap

Accepts: A hash (or hash reference) containing a series of keyname->elementname mappings or [none].

Returns: The current keymap hash (as a plain hash, or hash reference depending on caller context).

When called with a hash (hash reference) as its argument, this method sets/resets the entire internal keyname->elementname mappings definitions (where 'keyname' means the name of a given key in the hash and 'elementname' is the name used when firing SAX events for that key).

To add new mappings or remove existing ones without having to reset the whole list of mappings, see add_keymap() and delete_keymap() respectively.

If your are using "stream style" processing, this method should be used with caution since altering this mapping during processing may result in not-well-formed XML.

Examples:

$pd->keymap( keyname    => 'othername',
             anotherkey => 'someothername' );   

$pd->keymap( \%mymap );   

my %kmap_hash = $pd->keymap();   

my $kmap_hashref = $pd->keymap();   

add_keymap

Accepts: A hash (or hash reference) containing a series of keyname->elementname mappings.

Returns: [none]

Adds a series of keyname->elementname mappings (where 'keyname' means the name of a given key in the hash and 'elementname' is the name used when firing SAX events for that key).

Examples:

$pd->add_keymap( keyname => 'othername' );   

$pd->add_keymap( \%hash_of_mappings );   

delete_keymap

Accepts: A list (or array reference) of element/keynames.

Returns: [none]

Deletes a list of keyname->elementname mappings (where 'keyname' means the name of a given key in the hash and 'elementname' is the name used when firing SAX events for that key).

This method should be used with caution since altering this mapping during processing may result in not-well-formed XML.

Examples:

$pd->delete_keymap( 'some', 'key', 'names' );   

$pd->delete_keymap( \@keynames );   

skipelements

Accepts: A list (or array reference) containing a series of key/element names or [none].

Returns: The current skipelements array (as a plain list, or array reference depending on caller context).

When called with an array (array reference) as its argument, this method sets/resets the entire internal skipelement definitions (which determines which keys will not be 'parsed' during processing).

To add new mappings or remove existing ones without having to reset the whole list of mappings, see add_skipelements() and delete_skipelements() respectively.

Examples:

$pd->skipelements( 'elname', 'othername', 'thirdname' );

$pd->skipelements( \@skip_names );   

my @skiplist = $pd->skipelements();   

my $skiplist_ref = $pd->skipelements();   

add_skipelements

Accepts: A list (or array reference) containing a series of key/element names.

Returns: [none]

Adds a list of key/element names to skip during processing.

Examples:

$pd->add_skipelements( 'some', 'key', 'names' );   

$pd->add_skipelements( \@keynames );   

delete_skipelements

Accepts: A list (or array reference) containing a series of key/element names.

Returns: [none]

Deletes a list of key/element names to skip during processing.

Examples:

$pd->delete_skipelements( 'some', 'key', 'names' );   

$pd->delete_skipelements( \@keynames );   

attrmap

Accepts: A hash (or hash reference) containing a series of parent/child keyname pairs or [none].

Returns: The current attrmap hash (as a plain hash, or hash reference depending on caller context).

When called with a hash (hash reference) as its argument, this method sets/resets the entire internal keyname/elementname->attr children mappings definitions (where 'keyname' means the name of a given key in the hash and 'attr children' is list containing the nested keynames that should be passed as attributes of the element named 'keyname' (instead of as child elements).

To add new mappings or remove existing ones without having to reset the whole list of mappings, see add_attrmap() and delete_attrmap() respectively.

See CAVEATS for the limitations that relate to this method.

Examples:

$pd->attrmap( elname => ['list', 'of', 'nested', 'keynames' );

$pd->attr( \%mymap );   

my %attrmap_hash = $pd->attrmap();   

my $attrmap_hashref = $pd->attrmap();   

add_attrmap

Accepts: A hash or hash reference containing a series of parent/child keyname pairs.

Returns: [none]

Adds a series of parent-key -> child-key relationships that define which of the possible child keys will be processed as attributes of the created 'parent' element.

Examples:

$pd->add_attrmap( parentname =>  ['list', 'of', 'child', 'keys'] );   

$pd->add_attrmap( parentname =>  'childkey' );   

$pd->add_attrmap( \%parents_and_kids );   

delete_attrmap

Accepts: A list (or array reference) of element/keynames.

Returns: [none]

Deletes a list of parent-key -> child-key relationships from the instance-wide hash of "parent->nested names to pass as attributes" definitions. If you need to alter the list of child names (without deleting the parent key) use add_attrmap() to reset the parent-key's definition.

Examples:

$pd->delete_attrmap( 'some', 'parent', 'keys' );   

$pd->delete_attrmap( \@parentkeynames );   

bindattrs

Accepts: 1 or 0 or [none].

Returns: undef or 1 based on the current state of the bindattrs option.

Consider:

<myns:foo bar="quux"/>

and

<myns:foo myns:bar="quux"/>

are not functionally equivalent.

By default, attributes will be forwarded as not being bound to the namespace of the containing element (like the first example above). Setting this option to a true value alters that behavior.

Examples:

$pd->bindattrs(1); # attributes now bound and prefixed.

$pd->bindattrs(0); 

my $is_binding = $pd->bindattrs();  

add_namespace

Accepts: A hash containing the defined keys 'uri' and 'prefix'.

Returns: [none]

Add a namespace URI/prefix pair to the instance-wide list of XML namespaces that will be used while processing. The reserved prefix '#default' can be used to set the default (unprefixed) namespace declaration for elements.

Examples:

$pd->add_namespace( uri    => 'http://myhost.tld/myns',
                    prefix => 'myns' );

$pd->add_namespace( uri    => 'http://myhost.tld/default',
                    prefix => '#default' );

See namespacemap() or the namespacemap option detailed in new() for details about how to associate key/element name with a given namespace.

namespacemap

Accepts: A hash (or hash reference) containing a series of uri->key/element name mappings or [none].

Returns: The current namespacemap hash (as a plain hash, or hash reference depending on caller context).

When called with a hash (hash reference) as its argument, this method sets/resets the entire internal namespace URI->keyname/elementname mappings definitions (where 'keyname' means the name of a given key in the hash and 'namespace URI' is a declared namespace URI for the given process).

To add new mappings or remove existing ones without having to reset the whole list of mappings, see add_namespacemap() and delete_namespacemap() respectively.

If your are using "stream style" processing, this method should be used with caution since altering this mapping during processing may result in not-well-formed XML.

Examples:

$pd->add_namespace( uri    => 'http://myhost.tld/myns',
                    prefix => 'myns' );

$pd->namespacemap( 'http://myhost.tld/myns' => elname );

$pd->namespacemap( 'http://myhost.tld/myns' => [ 'list',  'of',  'elnames' ] );

$pd->namespacemap( \%mymap );   

my %nsmap_hash = $pd->namespacemap();   

my $nsmap_hashref = $pd->namespacemap();   

add_namespacemap

Accepts: A hash (or hash reference) containing a series of uri->key/element name mappings

Returns: [none]

Adds one or more namespace->element/keyname rule to the instance-wide list of mappings.

Examples:

$pd->add_namespacemap( 'http://myhost.tld/foo' => ['some', 'list', 'of' 'keys'] );

$pd->add_namespacemap( %new_nsmappings );

remove_namespacemap

Accepts: A list (or array reference) of element/keynames.

Returns: [none]

Removes a list of namespace->element/keyname rules to the instance-wide list of mappings.

Examples:

$pd->delete_namespacemap( 'foo', 'bar', 'baz' );   

$pd->delete_namespacemap( \@list_of_keynames );   

SAX EVENT METHODS

As a subclass of XML::SAX::Base, XML::Generator::PerlData allows you to call all of the SAX event methods directly to insert arbitrary events into the stream as needed. While its use in this way is probably a Bad Thing (and only relevant to "stream style" processing) it is good to know that such fine-grained access is there if you need it.

With that aside, there may be cases (again, using the "stream style") where you'll want to insert single elements into the output (wrapping each array in series of arrays in single 'record' elements, for example).

The following methods may be used to simplify this task by allowing you to pass in simple element name strings and have the result 'just work' without requiring an expert knowledge of the Perl SAX2 implementation or forcing you to keep track of things like namespace context.

Take care to ensure that every call to start_tag() has a corresponding call to end_tag() or your documents will not be well-formed.

start_tag

Accepts: A string containing an element name and an optional hash of simple key/value attributes.

Returns: [none]

Examples:

$pd->start_tag( $element_name );

$pd->start_tag( $element_name, id => $generated_id );

$pd->start_tag( $element_name, %some_attrs );

end_tag

Accepts: A string containing an element name.

Returns: [none]

Examples:

$pd->end_tag( $element_name );   

CAVEATS

In general, XML is based on the idea that every bit of data is going to have a corresponding name (Elements, Attributes, etc.). While this is not at all a Bad Thing, it means that some Perl data structures do not map cleanly onto an XML representation.

Consider:

my %hash = ( foo => ['one', 'two', 'three'] );

How do you represent that as XML? Is it three 'foo' elements, or is it a 'foo' parent element with 3 mystery children? XML::Generator::PerlData chooses the former. Or:

<foo>one</foo>
<foo>two</foo>
<foo>three</foo>

Now consider:

my @lol = ( ['one', 'two', 'three'], ['four', 'five', 'six'] );

In this case you wind up with a pile of elements named 'default'. You can work around this by doing $pd->add_keymap( default => ['list', 'of', 'names'] ) but that only works if you know how many entries are going to be in each nested list.

The practical implication here is that the current version of XML::Generator::PerlData favors data structures that are based on hashes of hashes for deeply nested structures (especally when using Simple Style processing) and some options like attrmap do not work for arrays at all. Future versions will address these issues if sanely possible.

AUTHOR

Kip Hampton, khampton@totalcinema.com

COPYRIGHT

(c) Kip Hampton, 2002, All Rights Reserved.

LICENCE

This module is released under the Perl Artistic Licence and may be redistributed under the same terms as perl itself.

SEE ALSO

XML::SAX.

cpanm XML::Generator::PerlData

perl -MCPAN -e shell
install XML::Generator::PerlData