Mechanism for user to "swap out" or "passthrough" an attribute of a class in the lutaml-model class tree

[ronaldtse]

In the oasis-etm gem, the <entry> element is meant to accept anything (in XML) that user wishes.

Clearly, this content won't be defined in the oasis-etm gem but by the user.

There are 2 ways the user wants to handle this:

• As passthrough, i.e. treat this content as a raw string.
• Swap the "attribute :content, :string" attribute of the Entry class to another Lutaml::Model::Serializable class.

In the first case, we need a way for the user to say that "give me this string as it is without parsing it as XML".

In the second case, we need a way for users of this gem to "swap out" the Entry class with their own "SpecialEntry" so they can process the content of Entry.

Both map_all and raw: true do not seem to be proper solutions to this use case.

Let's propose a syntax to support both cases..

Illustration from original issue

In the XML file, it contains this content:

<row>
  <entry>b1</entry>
  <entry>b2</entry>
  <entry>b3</entry>
  <entry>b4</entry>
  <entry morerows='1' valign='middle'><para>  <!-- Pernicous Mixed Content -->
  Vertical Span</para></entry>
</row>

The element <entry ...><para>...</para></entry> fails because the <para>...</para> content is not defined in lutaml-model, and therefore omitted from the re-generated content.

This is a case where the content of an element is not defined, and we need to implement some pass-through.

Clearly, map_all won't work here because we still need to retain the attributes.

So I thought of using raw: true:

module Oasis
  module Etm
    class Entry < Lutaml::Model::Serializable
      attribute :colname, :string
      attribute :content, :string, raw: true
      # ...

      xml do
        root "entry"

        # Attribute mappings
        map_attribute "colname", to: :colname
        # ...

        # Content mapping
        map_content to: :content
      end
    end
  end
end

But it still doesn't work.

Originally posted by @ronaldtse in https://github.com/lutaml/oasis-etm/issues/1#issuecomment-2451449564

[HassanAkbar]

@ronaldtse By looking at the issue I think

• We can allow map_attribute with map_all, With this we can map all the content and map attributes to different values or we can also give a map_all_attributes method to map all the attributes to a hash or string.
• We can allow something like Oasis::Etm::Entry.add_attribute or Oasis::Etm::Entry.add_element and also Oasis::Etm::Entry.remove_element, syntax can also be like Oasis::Etm::Entry.add("entry", type: :element)

@ronaldtse What do you think about this?

[ronaldtse]

We can allow map_attribute with map_all, With this we can map all the content and map attributes to different values or we can also give a map_all_attributes method to map all the attributes to a hash or string.

Then we should have "map_all", "map_all_content" and "map_all_attributes"?

We can allow something like Oasis::Etm::Entry.add_attribute or Oasis::Etm::Entry.add_element and also Oasis::Etm::Entry.remove_element, syntax can also be like Oasis::Etm::Entry.add("entry", type: :element)

Let me think...

[HassanAkbar]

Then we should have "map_all", "map_all_content" and "map_all_attributes"?

@ronaldtse Currently map_all is doing the same thing that we will be expecting from map_all_content. I think we can rename map_all to map_all_content and add a new method for map_all_attributes.

What do you suggest?

[ronaldtse]

we can rename map_all to map_all_content and add a new method for map_all_attributes

Agree. Let's do that.

However, we will still need a way to override a particular attribute/class in a lutaml-model class tree.

[HassanAkbar]

Agree. Let's do that.

Got it, I'm on it.

However, we will still need a way to override a particular attribute/class in a lutaml-model class tree.

For attributes, I'm thinking of keeping a hash because attributes will always be strings. So we can update the value of a single attribute for the element by changing the hash value.

For overriding the class I think we can provide methods to update attributes so we can change their type so it can be handled with different class. i.e Person.update_attribute(:name, { type: MyCustomStringClass }). Something like this.

@ronaldtse What do you think?