Painless OO XML with XML::Pastor - 2009 Remix

Painless OO <-> XML with XML::Pastor (2009 remix) Joel Bernstein YAPC::EU 2009

It’s all Greek to me schema σχήµα (skhēma) shape, plan

How many of you?

How many of you? • Use XML

How many of you? • Use XML • Hate XML

How many of you? • Use XML • Hate XML • Like XML

A Confession • I do not like XML • People use it wrong

XML Data Binding • Binding XML documents to objects speciﬁcally designed for the data in those documents. • I often have to do this.

XML is hard, right? Some hard things: • Roundtripping data • Manipulating XML via DOM API • Preserving element sibling order, comments, XML entities etc.

Typical horrendous XML document

Sales Order XML Logical data model XML DOM

I shouldn’t need to care about this

How this makes me feel:

Fundamental problem • I don’t think in elements and attributes • I think about my data, not how it’s stored • This is Perl. DWIM.

Solution Tools should make both the syntax and the details of the manipulation of XML invisible

Do you write XML

Do you write XML • By hand?

Do you write XML • By hand? • Programmatically?

Do you write XML • By hand? • Programmatically? • Schemata?

Do you write XML • By hand? • Programmatically? • Schemata? • Validation?

Do you write XML • By hand? • Programmatically? • Schemata? • Validation? • Transformation?

XML::Pastor is for all of you.

XML::Pastor • Available on CPAN • Abstracts away some of the pain of XML • Ayhan Ulusoy is the author • I am just a user

What does it do? • Generates Perl code from W3C XML Schema (XSD) • Roundtrip and validate XML to/from Perl without loss of schema information • Lets you program without caring about XML structure

pastorize • Automates codegen process • Conceptually similar to DBIC::Schema::Loader • TMTOWTDI - ofﬂine or runtime • Works on multiple XSDs (caveat, collisions)

pastorize in use pastorize --mode offline --style multiple --destination /tmp/lib/perl --class_prefix MyApp::Data /some/path/to/schema.xsd

Very simple contrived Album XML demo

Album XML document

Album XML schema

Pastorize the Album XML schema: Resulting code tree like:

Modify some XML

Roundtrip and modify XML data using Pastor: # Load XML # Accessors # Modify # Write XML

The result!

Real world Pastor

$HASH1 = { 1 => 'Vodafone UK', 2 => 'O2 UK', 3 => 'Orange UK', 4 => 'T-Mobile UK', 8 => 'Hutchinson 3 UK' }; Real world Pastor

Country XML

Dynamic schema parsing of Country XML

Query the Country object

Modify elements and attributes with uniform syntax

Manipulate array-like data

Create new City data and combine with existing Country object

Validate modiﬁed data against the stored schema

Turn Pastor objects back into XML, or transform to XML::LibXML DOM

Parsing with Pastor • Parse entire XML into XML::LibXML::DOM object • Convert XML DOM tree into native Perl objects • Throw away DOM, no longer needed

Reasons to not use XML::Pastor • When you have no XML Schema • Although several tools can infer XML schemata from documents • It’s a code-generator • No stream parsing

XML::Pastor Scope • Good for “data XML” • Unsuitable for “mixed markup” • e.g. XHTML • Unsuitable for “huge” documents

XML::Pastor known limitations • Mixed elements unsupported • Substitution groups unsupported • ‘any’ and ‘anyAttribute’ elements unsupported • Encodings (only UTF-8 ofﬁcially supported) • Default values for attributes - help needed

Other XML modules • XML::Twig • XML::Compile • XML::Simple • XML::Smart

XML::Twig • Manipulates XML directly • Using code is coupled closely to document structure • Optimised for processing huge documents as trees • No schemata, no validation

XML::Compile • Original design rationale is to deal with SOAP envelopes and WSDL documents • Different approach but similar goals to Pastor - processes XML based on XSD into Perl data structures • More like XML::Simple with Schema support

XML::Compile pt. 2 • Schema support incomplete • Shaky support for imports, includes • Include restriction on targetNamespace • I haven’t used it yet but it looks good

XML::Simple • Working roundtrip binding for simple cases • e.g. XMLout(XMLin($file)) works • Simple API • Produces single deep data structure • Gotchas with element multiplicity

XML::Simple pt. 2 • No schemata, no validation • Can be teamed with a SAX parser • More suitable for conﬁguration ﬁles?

XML::Smart • Similar implementation to XML::Pastor • Uses tie() and lots of crac^H^H^H^Hmagic • Gathers structure information from XML instance, rather than schema • No code generation!

XML::Smart pt. 2 • No schemata, so no schema validation • Based on Object::MultiType - overloaded objects as HASH, ARRAY, SCALAR, CODE & GLOB • Like Pastor, overloads array/hashref access to the data - promotes decoupling • Reasonable docs, some community growing

Any questions?

Thanks for coming See you next year http://search.cpan.org/dist/XML-Pastor/

Bonus Material If we have enough time

XML::Pastor Supported XML Schema Features • Simple and Complex Types • Global Elements • Groups, Attributes, AttributeGroups • Derive simpleTypes by extension • Derive complexTypes by restriction • W3C built-in Types, Unions, Lists • (Most) Restriction Facets for Simple types • External Schema import, include, redeﬁne

XML Schema Inference • Create an XML schema from an XML document instance • Every document has an (implicit) schema • Tools like Relaxer, Trang, as well as the System.Xml.Serializer the .NET Framework can all infer XML Schemata from document instances

Simple D::HA object

Rekeying data

Rekeying data deeper

Warning, boring bit

XML::Pastor Code Generation • Write out static code to tree of .pm ﬁles • Write out static code to single .pm ﬁle • Create code in a scalar in memory • Create code and eval() it for use

How Pastor works Code generation • Parse schemata into schema model • Perl data structures containing all the global elements, types, attributes, ... • “Resolve” Model - determine class names, resolve references, etc • Create boilerplate code, write out / eval

How Pastor works Generated classes • Each generated class (i.e. type) has classdata “XmlSchemaType” containing schema model • If the class isa SimpleType it may contain restriction facets • If the class isa ComplexType it will contain info about child elements and attributes

How Pastor works In use • If classes generated offline, then “use” them, if online then they are already loaded • These classes have methods to create, retrieve, save object to/from XML • Manipulate/query data using OO API to complexType fields • Validate modified objects against schema

Thanks for coming See you next year http://search.cpan.org/dist/XML-Pastor/

Painless OO XML with XML::Pastor - 2009 Remix

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