class XML::Mapping::SingleAttributeNode

Initializer. owner is the owning mapping class (gets passed to the superclass initializer and therefore put into @owner). The second parameter (and hence the first parameter to the node factory method), attrname, is a symbol that names the mapping class attribute this node should map to. It gets stored into @attrname, and the attribute (an r/w attribute of name attrname) is added to the mapping class (using attr_accessor).

In the initializer, two option arguments – :optional and :default_value – are processed in SingleAttributeNode:

Supplying :default_value=>obj makes obj the _default value_ for this attribute. When unmarshalling (loading) an object from an XML source, the attribute will be set to this value if nothing was provided in the XML; when marshalling (saving), the attribute won't be saved if it is set to the default value.

Providing just :optional=>true is equivalent to providing :default_value=>nil.

# File lib/xml/mapping/base.rb, line 662
def initialize(*args)
  @attrname,*args = super(*args)
  @owner.add_accessor @attrname
  if @options[:optional] and not(@options.has_key?(:default_value))
    @options[:default_value] = nil
  end
  initialize_impl(*args)
  args
end

utility method to be used by implementations of extract_attr_value. Calls the supplied block, catching XML::XXPathError and mapping it to NoAttrValueSet. This is for the common case that an implementation considers an attribute value not to be present in the XML if some specific sub-path does not exist.

# File lib/xml/mapping/base.rb, line 752
def default_when_xpath_err # :yields:
  begin
    yield
  rescue XML::XXPathError => err
    raise NoAttrValueSet, "Attribute #{@attrname} not set (XXPathError: #{err})"
  end
end

(to be overridden by subclasses) Extract and return the value of the attribute this node is responsible for (@attrname) from xml. If the implementation decides that the attribute value is “unset” in xml, it should raise NoAttrValueSet in order to initiate proper handling of possibly supplied :optional and :default_value options (you may use default_when_xpath_err for this purpose).

# File lib/xml/mapping/base.rb, line 713
def extract_attr_value(xml)
  raise "abstract method called"
end

this method was retained for compatibility with xml-mapping 0.8.

It used to be the initializer to be implemented by subclasses. The arguments (args) are those still unprocessed by SingleAttributeNode's initializer.

In xml-mapping 0.9 and up, you should just override initialize() and call super.initialize. The returned array is the same args array.

# File lib/xml/mapping/base.rb, line 679
def initialize_impl(*args)
end

(overridden) returns true if and only if the value of this node's attribute in obj is non-nil.

# File lib/xml/mapping/base.rb, line 761
def is_present_in? obj
  nil != obj.send(:"#{@attrname}")
end

(to be overridden by subclasses) Write value, which is the current value of the attribute this node is responsible for (@attrname), into (the correct sub-nodes, attributes, whatever) of xml.

# File lib/xml/mapping/base.rb, line 734
def set_attr_value(xml, value)
  raise "abstract method called"
end