Metabase::Resource - factory class for Metabase resource descriptors


version 0.025


  my $resource = Metabase::Resource->new(

  my $resource_meta = $resource->metadata;
  my $typemap       = $resource->metadata_types;


Metabase is a framework for associating metadata with arbitrary resources. A Metabase can be used to store test reports, reviews, coverage analysis reports, reports on static analysis of coding style, or anything else for which Metabase::Fact types are constructed.

Resources in Metabase are URI's that consist of a scheme and scheme specific information. For example, a standard URI framework for a CPAN distribution is defined by the URI::cpan class.


Metabase::Resource is a factory class for resource descriptors. It provide a common interface to extract scheme-specific indexing metadata from a scheme-specific resource subclass.

For example, the Metabase::Resource::cpan class will deconstruct the example above this into a Metabase resource metadata structure with the following elements:

  type         => Metabase-Resource-cpan-distfile
  dist_file    => RJBS/URI-cpan-1.000.tar.gz
  cpan_id      => RJBS
  dist_name    => URI-cpan
  dist_version => 1.000

Only the type field is mandatory for all resources. The other fields are all specific to Metabase::Resource::cpan.



  my $resource = Metabase::Resource->new(

Takes a single resource string argument and constructs a new Resource object from a resource subtype determined by the URI scheme. Throws an error if the required resource subclass is not available.


Returns the string used to initialize the resource object.


Returns a string containing the scheme.

_cache (private)

Returns a hash reference for subclasses to use to store data derived from the content string.


Resources have stringification overloaded to call content. Equality (==) and inequality (!=) are overloaded to perform string comparison instead.


Metabase::Resource relies on subclasses to implement scheme-specific parsing of the URI into relevant index metadata.

Subclasses SHOULD NOT implement a new constructor, as the Metabase::Resource constructor will load the subclass, construct the object, bless the object into the subclass, and then call validate on the object. Subclasses MAY store structured data derived from the content string during validation.

Subclasses SHOULD use the content method to access the resource string and the scheme method to access the scheme. Subclasses MAY use the _cache accessor to store derived metadata data. Subclasses MUST provide a metadata_types method to return data types for all elements stored in _cache.

All subclasses MUST implement the validate, metadata and metadata_types methods, as described below.

All methods MUST throw an exception if an error occurs.



This method is called by the constructor. It SHOULD return true if the resource string is valid according to scheme-specific rules. It MUST die if the resource string is invalid.


  $meta = $resource->metadata;

This method MUST return a hash reference with resource-specific indexing metadata for the Resource. The key MUST be the name of the field for indexing. The scheme key MUST be present and the scheme value MUST be identical to the string from the scheme accessor. Other keys SHOULD provide dimensions to differentiate one resource from another in the context of scheme. If a scheme has subcategories, the key type SHOULD be used for the subcategory. Values MUST be simple scalars, not references.

Here is a hypothetical example of a metadata function for a metabase user resource like 'metabase:user:ec2726a4-070c-11df-a2e0-0018f34ec37c':

  sub metadata {
    my $self = shift;
    my ($uuid) = $self =~ m{\Ametabase:user:(.+)\z};
    return {
      scheme  => 'metabase',
      type    => 'user',
      user    => $uuid,

Field names should be valid perl identifiers, consisting of alphanumeric characters or underscores. Hyphens and periods are allowed, but are not recommended.


  my $typemap = $resource->metadata_types;

This method is used to identify the datatypes of keys in the data structure provided by metadata. It MUST return a hash reference. It SHOULD contain a key for every key that could appear in the data structure generated by metadata and provide a value corresponding to a datatype for each key. It MAY contain keys that do not always appear in the result of metadata.

Data types are loosely based on Data::RX. Type SHOULD be one of the following:

  '//str' -- indicates a value that should be compared stringwise
  '//num' -- indicates a value that should be compared numerically

Here is a hypothetical example of a metadata_types function for a metabase user resource like 'metabase:user:ec2726a4-070c-11df-a2e0-0018f34ec37c':

  sub metadata_types {
    return {
      scheme  => '//str',
      type    => '//str',
      user    => '//str',

Consumers of metadata_types SHOULD assume that any metadata key not found in the result of metadata_types is a '//str' resource.


Please report any bugs or feature using the CPAN Request Tracker. Bugs can be submitted through the web interface at

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.


  • David Golden <>

  • Ricardo Signes <>

  • H.Merijn Brand <>


This software is Copyright (c) 2016 by David Golden.

This is free software, licensed under:

  The Apache License, Version 2.0, January 2004