[xsd-users] Question about ID/IDREF

[Vera Mickael]

Boris Kolpackov a écrit :
> Mickael,
> 
> Vera Mickael <vera.mickael at free.fr> writes:
> 
> 
>>Each time I use ID and IDREF, the method in the generated
>>model for the attribute that uses IDREF returns a
>>java.lang.Object. This makes the generated model very
>>difficult to use.
> 
> 
> Ok, you mean you have to manually cast it to a concrete type.
> 
> 
> 
>>Does xsd generate the same (a method that returns void *) ?
> 
> 
> At the moment, xsd generates a member function that returns
> a pointer to a type that all generated types inherit from
> (similar to java.lang.Object). You have to cast this pointer
> to a concrete one.
> 
> 
>>Or is there a way to specify the type of the element
>>referenced by IDREF, by annotations for example ?
> 
> 
> Not at the moment but we have plans to do so. The idea is
> to have an attribute that you can use to specify the "real
> type" of IDREF, e.g.:
> 
> <xsd:complexType name="author">
> 
>   ...
> 
>   <xsd:attribute name="recommends"
>                  type="xsd:IDREF"
>                  ref-type="lib:book"/>
> </xsd:complexType>
> 
> 
> <xsd:complexType name="book">
>   <xsd:sequence>
>     <xsd:element name="title" type="xsd:string"/>
> 
>     ...
> 
>   </xsd:sequence>
> 
>   <xsd:attribute name="id" type="xsd:ID" use="required"/>
> </xsd:complexType>
> 
> 
> Then you will be able to write something like this:
> 
> author a = ...
> 
> cerr << a.recommends ()->title () << endl;
> 
> 
> Would you be interested in something like this?
> 
> -boris
> 

Your solution with ref-type attribute is better than using 
annotations :-)

Yes I would be interested in such a feature, I'm kind on 
statically typed programmation and JAXB really lacks about 
this. It makes it really difficult to change the schema. It 
would be a feature usefull for everybody.

This question raises another one.

I'd like to use xsd as a simple serialization tool, my point 
of view is model centric : I know the model I want (thus the 
C++ code I need) then I write the corresponding XML schema.

How would you write a schema for a collection of IDREF 
without using an intermediate element ? If I use your 
exemple, I'd like to have a method like this :

std::vector<book *> &
author::recommends();

My only idea is to create a element bookRef with an 
attribute referencing a book and use this element bookRef in 
a sequence in the element author. I guess that I would have 
the following code that isn't as elegant as the previous :

std::vector<bookRef> &
author::recommends();

Thanks for your answer,
Mickaël