feat: add map_all for xml mapping

[HassanAkbar]

Added map_all for mapping all content inside an XML tag to an attribute.

fixes #57
can be used for -> #106

[ronaldtse]

@HassanAkbar looks good! Could you please help document this in the README with an example? Thanks.

[ronaldtse]

@HassanAkbar what happens with map_all when the format is JSON? Does this mean that a class that uses map_all cannot do JSON etc?

[HassanAkbar]

@ronaldtse Yes this PR only adds map_all for XML mappings, For JSON we do not need the map_all method because our internal representation is hash and we can map an attribute to a string, something like below and it will work

person = { 
  name: "test", 
  age: "20", 
  description: { title: "foobar", awards: "many" }
}.to_json

class Person < Lutaml::Model::Serializable
  attribute :name, :string
  attribute :age, :integer
  attribute :description, :string
  
  json do
    map "name", to: :name
    map "age", to: :age
    map "description", to: :description
  end
end

Person.from_json(person)
#<Person:0x00000001044dd9b0                                     
 @age=20,                                                       
 @description="{\"title\"=>\"foobar\", \"awards\"=>\"many\"}",  
 @name="test",                                                  
 @using_default={:name=>false, :age=>false, :description=>false},
 @validate_on_set=false> 

I will open a separate PR for YAML and toml.
I added this only in a separate PR because this was marked urgent and has been in progress for a long time.

[ronaldtse]

I think what I don't understand is, how does the concept of map_all work with JSON, YAML and TOML?

JSON is like: { "attr" : "value" }. Does that mean map_all will give the raw value of { "attr" : "value" }?

YAML is like: attr: value. Does that mean map_all will give the raw value?

Does map_all on this element produce:

<element>
  <one>text</one>
</element>

1. The entire element?

<element attr=1>
  <one>text</one>
</element>

2. Only the inner content of the element?

  <one>text</one>

[HassanAkbar]

@ronaldtse the map_all will work by assigning everything inside the tag or the key it is defined in. for example

• For XML

  map_all will assign all the content inside that tag but will not assign the attributes in the current tag. i.e

  class Element < Lutaml::Model::Serializable
    attribute :all_content, :string
    
    xml do
      map_all to: :all_content
    end
  end

  <element attr1="1">
    <one attr2="2" attr3="3">text</one>
  </element>

  Element.from_xml(xml).all_content
  > "<one attr2=\"2\" attr3=\"3\">text</one>"

• For YAML, JSON, and TOML

  map_all will assign all the content against the key to the model attribute. i.e

  class Element < Lutaml::Model::Serializable
    attribute :all_content, :string
    
    yaml do
      map_all to: :all_content
    end
    
    json do
      map_all to: :all_content
    end
  
    toml do
      map_all to: :all_content
    end
  end

  YAML Example

  element:
  - another_element
  - element_with_childs
    name: "John"

  Element.from_yaml(yaml).all_content
  > "- another_element\n- element_with_childs\n  name: \"John\""

  JSON Example

  { 
    "element": [
      "another_element",
      "element_with_childs": { "name": "John" }
    ]
  }

  Element.from_json(json).all_content
  > "[\"another_element\", \"element_with_childs\": {\"name\": \"John\"}]"