Be strict about adherence to cardinality via collection: true

[ronaldtse]

From:

• The attribute standard_relationship should be a collection relaton/ieee-idams#6

Currently, if an attribute does not define collection: true, lutaml-model accepts all 3 cases:

• 0 occurrences
• 1 occurrence
• N occurrences

However, collection: true means 0..*, and collection: false (default) means 0..1. Right now, the default of 0..1 does not raise any error if there are more than 1 occurrence.

When the XML/JSON does not fit this model definition, it should raise an error.

[0arm0]

@ronaldtse I was looking into this issue and I tried to raise an error on invalid cardinality such that the input has multiple elements but we don’t have collection: true defined in our attribute.

So, in this case, map_content raises an error since multiple content lines are mapped to a single content attribute in an Array, which raises a cardinality error. For example:

xml = <<~XML <RootOrderedContent id="123">
  <bold>bell</bold>
  <italic>384,400 km</italic>
  <underline>craters</underline>
  <bold>cool</bold>
  The Earth's Moon rings like a  when struck by
  meteroids. Distanced from the Earth by ,
  its surface is covered in . Ain't that ?
</RootOrderedContent>
XML

When mapped to:

class RootOrderedContent < Lutaml::Model::Serializable
    attribute :id, :string
    attribute :bold, :string, collection: true
    attribute :italic, :string, collection: true
    attribute :underline, :string
    attribute :content, :string

    xml do
      root "RootOrderedContent", ordered: true
      map_attribute :id, to: :id
      map_element :bold, to: :bold
      map_element :italic, to: :italic
      map_element :underline, to: :underline
      map_content to: :content
    end
  end

serialized = OrderedContentSpec::RootOrderedContent.from_xml(xml)
serialized.content #=> ["\n  The Earth's Moon rings like a ", " when struck by\n  meteroids. Distanced from the Earth by ", ",\n  its surface is covered in ", ".\n  Ain't that ", "?\n"]

So this content, when mapped to :content attribute, would raise cardinality error if we implement this strictness.
A solution that I can think of is to bypass the :content attribute (from my example) from this error check so that no error is raised.
Let me know what do you suggest here please?