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Manual Reference Pages  -  XML::PATACT::TOOBJECTS (3)

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NAME

XML::PatAct::ToObjects - An action module for creating Perl objects

CONTENTS

SYNOPSIS



 use XML::PatAct::ToObjects;

 my $patterns = [ PATTERN => [ OPTIONS ],
                  PATTERN => "PERL-CODE",
                  ... ];

 my $matcher = XML::PatAct::ToObjects->new( Patterns => $patterns,
                                            Matcher => $matcher,
                                            CopyId => 1,
                                            CopyAttributes => 1 );



DESCRIPTION

XML::PatAct::ToObjects is a PerlSAX handler for applying pattern-action lists to XML parses or trees. XML::PatAct::ToObjects creates Perl objects of the types and contents of the action items you define.

New XML::PatAct::ToObject instances are creating by calling ‘new()’. Parameters can be passed as a list of key, value pairs or a hash. ‘new()’ requires the Patterns and Matcher parameters, the rest are optional:
Patterns The pattern-action list to apply.
Matcher An instance of the pattern or query matching module.
CopyId Causes the ‘ID’ attribute, if any, in a source XML element to be copied to an ‘ID’ attribute in newly created objects. Note that IDs may be lost of no pattern matches that element or an object is not created (-make) for that element.
CopyAttributes Causes all attributes of the element to be copied to the newly created objects.
Each action can either be a list of options defined below or a string containing a fragment of Perl code. If the action is a string of Perl code then simple then some simple substitutions are made as described further below.

Options that can be used in an action item containing an option-list:
<B>-holderB> Ignore this element, but continue processing it’s children (compare to <B>-ignoreB>). -pcdata may be used with this option.
<B>-ignoreB> Ignore (discard) this element and it’s children (compare to <B>-holderB>).
<B>-pcdataB> Character data in this element should be copied to the Contents field.
<B>-makeB> PACKAGE Create an object blessed into PACKAGE, and continue processing this element and it’s children. PACKAGE may be the type ‘HASH’ to simply create an anonyous hash.
<B>-argsB> ARGUMENTS Use ARGUMENTS in creating the object specified by <B>-makeB>. This is commonly used to copy element attributes into fields in the newly created object. For example:



  -make => HASH, -args => URL => %{href}



would copy the ‘href’ attribute in an element to the ‘URL’ field of the newly created hash.

<B>-fieldB> FIELD Store this element, object, or children of this element in the parent object’s field named by FIELD.
<B>-push-fieldB> FIELD Similar to <B>-fieldB>, except that FIELD is an array and the contents are pushed onto that array.
<B>-valueB> VALUE Use VALUE as a literal value to store in FIELD, otherwise ignoring this element and it’s children. Only valid with <B>-fieldB> or <B>-push-fieldB>. ‘%{ATTRIBUTE}’ notation can be used to substitute the value of an attribute into the literal value.
<B>-as-stringB> Convert the contents of this element to a string (as in XML::Grove::AsString) and store in FIELD. Only valid with <B>-fieldB> or <B>-push-fieldB>.
<B>-groveB> Copy this element to FIELD without further processing. The element can then be processed later as the Perl objects are manipulated. Only valid with <B>-fieldB> or <B>-push-fieldB>. If ToObjects is used with PerlSAX, this will use XML::Grove::Builder to build the grove element.
<B>-grove-contentsB> Used with <B>-makeB>, <B>-grove-contentsB> creates an object but then takes all of the content of that element and stores it in Contents.
If an action item is a string, that string is treated as a fragment of Perl code. The following simple substitutions are performed on the fragment to provide easy access to the information being converted:
<B>B>@ELEM<B>@B> The object that caused this action to be called. If ToObjects is used with PerlSAX this will be a hash with the element name and attributes, with XML::Grove this will be the element object, with Data::Grove it will be the matching object, and with XML::DOM it will be an XML::DOM::Element.

EXAMPLE

The example pattern-action list below will convert the following XML representing a Database schema:



    <schema>
      <table>
        <name>MyTable</name>
        <summary>A short summary</summary>
        <description>A long description that may
          contain a subset of HTML</description>
        <column>
          <name>MyColumn1</name>
          <summary>A short summary</summary>
          <description>A long description</description>
          <unique/>
          <non-null/>
          <default>42</default>
        </column>
      </table>
    </schema>



into Perl objects looking like:



    [
      { Name => "MyTable",
        Summary => "A short summary",
        Description => $grove_object,
        Columns => [
          { Name => "MyColumn1",
            Summary => "A short summary",
            Description => $grove_object,
            Unique => 1,
            NonNull => 1,
            Default => 42
          }
        ]
      }
    ]



Here is a Perl script and pattern-action list that will perform the conversion using the simple name matching pattern module XML::PatAct::MatchName. The script accepts a Schema XML file as an argument ($ARGV[0]) to the script. This script creates a grove as one of it’s objects, so it requires the XML::Grove module.



    use XML::Parser::PerlSAX;
    use XML::PatAct::MatchName;
    use XML::PatAct::ToObjects;

    my $patterns = [
      schema      => [ qw{ -holder                                  } ],
      table       => [ qw{ -make Schema::Table                      } ],
      name        => [ qw{ -field Name -as-string                   } ],
      summary     => [ qw{ -field Summary -as-string                } ],
      description => [ qw{ -field Description -grove                } ],
      column      => [ qw{ -make Schema::Column -push-field Columns } ],
      unique      => [ qw{ -field Unique -value 1                   } ],
      non-null    => [ qw{ -field NonNull -value 1                  } ],
      default     => [ qw{ -field Default -as-string                } ],
    ];

    my $matcher = XML::PatAct::MatchName->new( Patterns => $patterns );
    my $handler = XML::PatAct::ToObjects->new( Patterns => $patterns,
                                               Matcher => $matcher);

    my $parser = XML::Parser::PerlSAX->new( Handler => $handler );
    my $schema = $parser->parse(Source => { SystemId => $ARGV[0] } );



TODO

o It’d be nice if patterns could be applied even in <B>-as-stringB> and <B>-groveB>.
o Implement Perl code actions.
o <B>-as-xmlB> to write XML into the field.

AUTHOR

Ken MacLeod, ken@bitsko.slc.ut.us

SEE ALSO

perl(1), Data::Grove(3)

‘‘Using PatAct Modules’’ and ‘‘Creating PatAct Modules’’ in libxml-perl.

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perl v5.20.3 XML::PATACT::TOOBJECTS (3) 2003-10-21

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