NAME

Struct::Flatten::Template - flatten data structures using a template

SYNOPSIS

  use Struct::Flatten::Template;

  my $tpl = {
    docs => [
      {
         key => \ { column => 0 },
         sum => {
            value => \ { column => 1 },
      }
    ],
  };

  my @data = ( );

  my $hnd = sub {
    my ($obj, $val, $args) = @_;

    my $idx = $args->{_index};
    my $col = $args->{column};

    $data[$idx] ||= [ ];
    $data[$idx]->[$col] = $val;
  };

  my $data = {
    docs => [
      { key => 'A', sum => { value => 10 } },
      { key => 'B', sum => { value =>  4 } },
      { key => 'C', sum => { value => 18 } },
    ],
  };

  my $p = Struct::Flatten::Template->new(
    template => $tpl,
    handler  => $hnd,
  );

DESCRIPTION

This module is used for "flattening" complex, deeply-nested data structures, such as those returned by an ElasticSearch aggregation query.

It is configured with a "template" that mirrors the data structure, where some parts of the template contain information how to process the corresponding parts of the data structure.

ATTRIBUTES

template

This is a template of the data structure.

This is basically a copy of the data structure, with the hash reference keys and values that you care to extract information from, using the "handler".

To obtain a value, set it to a reference to a hash reference, e.g.

  key => \ { ... }

The keys in the hash reference can be whatever youre application needs, so long as they are not prefixed with an underscore.

The following special keys are used:

_index

This is either the array index of hash key or array item that the value is associated with.

Note that this is deprecated, and may be removed in future versions. Use "_path" instead.

_sort

If set, this is a method used to sort hash keys, when the template refers to a list of hash keys, e.g.

  key => \ {
             _sort => sub { $_[0] cmp $_[1] },
             ...
           }

_next

If your template is for hash keys instead of values, then this refers to the value of that hash key in the template.

It is useful if you want to have your handler fill-in intermediate values (e.g. gaps in a list of dates) by calling the "process" method.

_path

This contains an array reference of where in the data structure the handler is being called.

The array is of the form

  $key1 => $type1, $key2 => $type2, ...

where the keys refer to hash keys or array indices, and the types are either HASH or ARRAY.

Note: to trigger a callback on hash keys instead of values, use Tie::RefHash.

Also note that templates for array references assume the first element applies to all elements of the data structure being processed.

is_testing

This is true if the template is being processed using "test".

This is useful to extract meta-information from your template, e.g. field titles.

It is intended to be used from within the "handler".

ignore_missing

If true, missing substructures will be ignored and the template will be processed. This is useful for setting default values for missing parts of the structure.

This is true by default.

handler

The handler is a reference to a function, e.g.

  sub {
    my ($obj, $value, $args) = @_;

    if ($obj->is_testing) {
      ...
    } else {
      ...
    }
  }

where $obj is the Struct::Flatten::Template object, $value is the value from the data structure being processed, and $args is a hash reference from the template.

Note that $args may have additional keys added to it. See "template".

Your handler will need to use the information in $args to determine what to do with the data, e.g., where in a spreadsheet or what column in a database to it.

METHODS

run

  $obj->run( $struct );

Process $struct using the "template".

test

  $obj->test();

Test the template. Essentially, it processes the "template" against itself.

process

process_HASH

process_ARRAY

  $obj->process($struct, $template, $index);

These are low-level methods for processing the template. In general, you don't need to worry about them unless you are subclassing this.

If you are inserting intermediate values from within your handler, you should be calling the process method.

SEE ALSO

The following alternative modules can be used to flatten hashes:

Data::Hash::Flatten

Hash::Flatten

AUTHOR

Robert Rothenberg, <rrwo at cpan.org>

ACKNOWLEDGEMENTS

Foxtons, Ltd.

LICENSE AND COPYRIGHT

Copyright 2014 Robert Rothenberg.

This program is free software; you can redistribute it and/or modify it under the terms of the the Artistic License (2.0). You may obtain a copy of the full license at:

http://www.perlfoundation.org/artistic_license_2_0

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This license includes the non-exclusive, worldwide, free-of-charge patent license to make, have made, use, offer to sell, sell, import and otherwise transfer the Package with respect to any patent claims licensable by the Copyright Holder that are necessarily infringed by the Package. If you institute patent litigation (including a cross-claim or counterclaim) against any party alleging that the Package constitutes direct or contributory patent infringement, then this Artistic License to you shall terminate on the date that such litigation is filed.

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