Forum: Ruby accessing one class from another class

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Fd1a879445f337144bc1f2a5ebd8402b?d=identicon&s=25 nick ger (konung)
on 2009-05-04 23:39
Hello, All.

I'm trying to consuming an xml file and map it to a Ruby object that
would describe that xml file.

What would be the best way to implement the following scenario.

Let's say I have several classes: Student, Course, Person, Tuition
Xml for this would look like this:
<Record>
<Student status="good">
  <Person>
    <Name>Alice</Name>
    <BirthPlace>WonderLand</BirthPlace>
  </Person>
  <Course difficulty=">
    <CourseName>Math III</CourseName>
    <Grade>B+</Grade>
  </Course>
  <dt:Tuition>
    <dt:Currency>USD</dt:Currency>
    <dt:Amount>500</dt:Amount>
    <dt:Period>3 months</dt:Period>
  </dt:Tuition>
</Student>
</Record>
So basically I can parse the xml file using rexml and access all of my
xml tags and stuff.

Here is the Object I want to map it to:


class Student
 @status
 @person - access Person
end

class Person
end

class Course
end

class Tution
end



So the question is how do I access from class Student - class Person? So
that when I down the line later when I parse the file and do:

r = Record.new

I want to be able to do things like:
r.student.person.name

????


Thank you
Fd1a879445f337144bc1f2a5ebd8402b?d=identicon&s=25 nick ger (konung)
on 2009-05-04 23:42
Also to clarify xml tag like <Course> can be repeated in my xml file,
so:

r.student.course
could return an array of objects of class Course.
Fd1a879445f337144bc1f2a5ebd8402b?d=identicon&s=25 nick ger (konung)
on 2009-05-05 00:05
To clarify Futhre I'm doing somethign like this right now:

class Base

  attr_accessor :name, :value

  def initialize
    @name
    @value
  end
end

class Student
  attr_accessor :person, :tuition

  def initialize
    @person = Person.new
    @tuition = Tuition.new
  end

end

... define Tuition & Person class. I'm just looking for a better way to
do it.

Also how would I properly define :course within Student, considering
that I might have a single Course or multiple - depending on the record.

Thank you
72c015d3601e275d5ee8a214e89cf03a?d=identicon&s=25 Alex Eiras (Guest)
on 2009-05-05 00:08
(Received via mailing list)
> Also to clarify xml tag like <Course> can be repeated in my xml file,
> so:
>
> r.student.course
> could return an array of objects of class Course.
> --
>


Hi Nick,

There are some good libraries to accomplish this. You may want to have a
look at one of these (ordered by my own preferences):

xml-object:
http://github.com/jordi/xml-object/tree/master

happy-mapper:
http://happymapper.rubyforge.org/

xml-mapping:
http://xml-mapping.rubyforge.org/

Hope it helps
Cheers
Fd1a879445f337144bc1f2a5ebd8402b?d=identicon&s=25 nick ger (konung)
on 2009-05-05 00:40
Thank you Alex, but no go :-(

I looked into all of them - they all lack in some respect:
happy-mapper - can't build xml & handle namespaces
xml-object can't handle namespaces - and some other issue - can't
remember
xml-mapping - same thing
roxml - same problem.

So the solution is to just do it myself. However that wasn't my question
- it was more a of generic ruby class question.
E0d864d9677f3c1482a20152b7cac0e2?d=identicon&s=25 Robert Klemme (Guest)
on 2009-05-05 08:33
(Received via mailing list)
On 04.05.2009 23:39, Nick da G wrote:
> <Student status="good">
>     <dt:Amount>500</dt:Amount>
> class Student
> class Tution
> r.student.person.name
You can define attributes via attr_accessor, e.g.

class Student
   attr_accessor :person
end

class Person
   attr_accessor :name
end

st = Student.new
pe = Person.new
pe.name = "Nick"
st.person = pe

etc.

As a shortcut you can as well use Struct:

Student = Struct.new :person
Person = Struct.new :name

Kind regards

  robert
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