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Date: Thu, 06 Nov 2003 18:43:51 +0100
From: Ugo Cei <u.cei@cbim.it>
Organization: C.B.I.M.
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To: dev@cocoon.apache.org
Subject: [Proposal] Add "enum" basetype and convertor to Woody
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I'd like to add an "enum" basetype and "enum" convertor to Woody. Those 
would work with types implementing Joshua Bloch's "typesafe enum" 
pattern [1].

The reason for this is as follows: when representing business entities 
with Java objects, I always try to assign a significant type to fields 
that can assume a value taken from a list, e.g.

package com.example;

public class Person {
   private Sex sex;
   ...
}

public class Sex {
   public static final Sex MALE = new Sex("M");
   public static final Sex FEMALE = new Sex("F");
   private String code;

   private Sex(String code) { this.code = code; }
   public String toString() {
     return code; // Will probably have some i18n support here
   }
}

...

person.setSex(Sex.FEMALE);

...

Currently, in Woody we cannot directly bind form fields to objects of 
type "Sex" and it would be cumbersome to add a datatype and convertor 
for every possible enum (there could be many in even a small 
application) in cocoon.xconf. So we have to resort to manually 
converting to and from enums and strings (or integers).

I am thinking about adding something that might allow to specify:

<wd:field id="sex">
   <wd:datatype base="enum">
     <wd:convertor type="enum">
       <wd:enum>com.example.Sex</wd:enum>
     </wd:convertor>
   </wd:datatype>
</wd:field>

Maybe we could also generate a selection list from the enum type.

One possible problem could be that the enum type must implement an 
interface providing methods for converting to/from strings or integers. 
This could be impossible or problematic when dealing with existing 
classes. However, I haven't really thought about the implementation, yet.

	WDYT?

		Ugo

[1]: 
http://developer.java.sun.com/developer/Books/shiftintojava/page1.html#replaceenums

-- 
Ugo Cei - Consorzio di Bioingegneria e Informatica Medica
P.le Volontari del Sangue, 2 - 27100 Pavia - Italy
Phone: +39.0382.525100 - E-mail: u.cei@cbim.it