Accessors (was Re: Adding cocoon.suicide() to the FOM API.)

[Sylvain Wallez <sy...@apache.org>]

Daniel Fagerstrom wrote:

> Sylvain Wallez wrote:
>
>> Daniel Fagerstrom wrote: 
>
>
> <snip/>
>
>>> BTW, concerning what to call the "object accessors", what about just 
>>> "accessor", e.g. RequestAccessor, SessionAccessor etc.
>>
>>
>> "RequestObjectAccessor" or "SessionObjectAccessor" really would be 
>> too verbose, but "ObjectAccessor" for the general interface is maybe 
>> less abstract than simply "Accessor".
>
>
> Its also ok.
>
>> Now talking about abstraction, it will be more difficult to write 
>> something more abstract than an interface having a single "Object 
>> get()" method ;-) 
>
>
> The Component marker interface was a little bit more abstract ;)


Oh yes, forgot about that one ;-)

>> Well...
>
>
> I can agree that it seem to break some common ideas about good coding 
> practice. But we have been through the arguments and it seem OK. We 
> probably find out if it works when we start to implement and integrate it.


Oh yes, sure. I totally agree with the concept. It's not a factory and 
it's not an object holder as depending on the implementation it can be 
either or even something else. So accessor is fine!

Sylvain

-- 
Sylvain Wallez                                  Anyware Technologies
http://www.apache.org/~sylvain           http://www.anyware-tech.com
{ XML, Java, Cocoon, OpenSource }*{ Training, Consulting, Projects }

Re: Accessors (was Re: Adding cocoon.suicide() to the FOM API.)

[Daniel Fagerstrom <da...@nada.kth.se>]

Ralph Goers wrote:
> Daniel Fagerstrom wrote:
>> Ralph Goers wrote:
<snip/>
>>> Is this what I hope it means?  If it is, then I hope to see classes 
>>> like Request, Session, Context, etc. be modified to implement the 
>>> interface.  To me, this would mean that they implement a static get 
>>> method that returns the appropriate instance of the object.  Perhaps 
>>> a better name for this would be Accessible.  I guess your plan is to 
>>> implement a separate Accessor class to do this instead?
>>
>> I'm not geting what your aim at, could you tell a little bit about how 
>> you want to use the accessores so that I can understand why you prefer 
>> such a solution compared to the component based approach that we have 
>> discussed.
> 
> Actually, a couple approaches have been mentioned.  As I understand 
> them, they are:
> 1.   Have a global "component object model" that everything is anchored 
> in and accessed through.

Like FOM which in turn is modeled after the browser object model in web 
browsers. Part of the idea IIRC was that it should be natural to used 
for people who had used JS in browsers.

> Frankly, I see this as a bad idea that needs 
> to go away - at least the accessing part.  There are so many reasons why 
> this is awful that I don't even want to start listing them. But just for 
> a start, it is hardly object oriented as it makes the component object 
> model have to know way too much.

It data oriented rather than object oriented. If that is good or bad 
depends on your perspective. For accessing the kind of data that we have 
in FOM it is OK for me. So I guess that you have to list some of your 
agruments anyway if you want me to understand why its awful.

> 2.  Have an Accessor interface, presumably with a class that implements 
> it for each type of object to be accessed, such as RequestAccessor, 
> SessionAccessor, etc.  In and of itself, this isn't a bad idea.  It just 
> isn't necessary, in my opinion.
> 
> When I was working on my last portal enhancements, I was frustrated that 
> I couldn't get ahold of some of the objects I needed.  The "right way" 
> would have required that I make some of the classes implement Avalon 
> interfaces which, of course, meant adding more definitions to 
> cocoon.xconf.  This is frustrating when all you want is to the reference 
> to some other object, but to get it you have to have a Context or a 
> service manager.  It would be much more convenient for a lot of objects, 
> as well as many flow applications, to be able to just do:
> Object.getInstance();

Ok, if your webapps contains a lot of custom Java code I can understand 
that the Avalon way can be frustrating. The webapps that we build where 
I work contains very small amounts of custom Java code. For us having 
things configurable is an advantage rather than the opposite.

> This places the burden for locating the correct object instance on the 
> object itself which, in my opinion, is where it belongs.  It also allows 
> the object to use any number of techniques to locate the correct 
> instance; it can retrieve it from the object model, from the component 
> manager, or whatever.

I don't know, IOC component managers where IIUC invented because some 
people had bad experiences with the scalability for direct object 
access. I have used that paradigm for so long that I don't remember what 
problems I might have had before ;) But I think Cocoon is easier to use 
and maintain if we follow the same design patterns everywhere.

Don't you think some of the problems that you describe above becomes 
smaller if we introduce the possibility to use modern containers like 
Spring and Hivemind in application code, like Carsten proposed?

I don't see the accessors as a general way to integrate business objects 
in Cocoon but just as a evolution of the input/output module concept 
that is better adapted to the needs in templates and flow and not only 
to the needs for the sitemap.

> Furthermore, it allows one to write something 
> like ${Request} in a template or flowscript and have that be replaced 
> with a reference to the correct object instance.

How does the template know in what package to find the Request object? 
And how does it know if it should use the http or command line variant?

I get the feeling that one have to rebuild quite a lot of the 
architecture that we already have from Avalon if we follow the 
X.getInstance() way.

> Is that clearer?

It is. But to me it seem like we are attacking different problem areas, 
and I'm not certain that they should be solved with the same tool.

/Daniel

Re: Accessors (was Re: Adding cocoon.suicide() to the FOM API.)

[Ralph Goers <Ra...@dslextreme.com>]

Daniel Fagerstrom wrote:

> Ralph Goers wrote:
>
>> Sylvain Wallez wrote:
>>
>>> Oh yes, sure. I totally agree with the concept. It's not a factory 
>>> and it's not an object holder as depending on the implementation it 
>>> can be either or even something else. So accessor is fine!
>>
>> Did this accessor thing evolve from another discussion?  It seemed to 
>> pop up out of thin air in this thread.
>
> It did, I had thought a little bit more about what to call them and 
> wanted to tell, Sylvain decreased the confussion by changing the 
> thread name.
>
>> Is this what I hope it means?  If it is, then I hope to see classes 
>> like Request, Session, Context, etc. be modified to implement the 
>> interface.  To me, this would mean that they implement a static get 
>> method that returns the appropriate instance of the object.  Perhaps 
>> a better name for this would be Accessible.  I guess your plan is to 
>> implement a separate Accessor class to do this instead?
>
>
> I'm not geting what your aim at, could you tell a little bit about how 
> you want to use the accessores so that I can understand why you prefer 
> such a solution compared to the component based approach that we have 
> discussed.

Actually, a couple approaches have been mentioned.  As I understand 
them, they are:
1.   Have a global "component object model" that everything is anchored 
in and accessed through.  Frankly, I see this as a bad idea that needs 
to go away - at least the accessing part.  There are so many reasons why 
this is awful that I don't even want to start listing them. But just for 
a start, it is hardly object oriented as it makes the component object 
model have to know way too much.
2.  Have an Accessor interface, presumably with a class that implements 
it for each type of object to be accessed, such as RequestAccessor, 
SessionAccessor, etc.  In and of itself, this isn't a bad idea.  It just 
isn't necessary, in my opinion.

When I was working on my last portal enhancements, I was frustrated that 
I couldn't get ahold of some of the objects I needed.  The "right way" 
would have required that I make some of the classes implement Avalon 
interfaces which, of course, meant adding more definitions to 
cocoon.xconf.  This is frustrating when all you want is to the reference 
to some other object, but to get it you have to have a Context or a 
service manager.  It would be much more convenient for a lot of objects, 
as well as many flow applications, to be able to just do:
    Object.getInstance();

This places the burden for locating the correct object instance on the 
object itself which, in my opinion, is where it belongs.  It also allows 
the object to use any number of techniques to locate the correct 
instance; it can retrieve it from the object model, from the component 
manager, or whatever.  Furthermore, it allows one to write something 
like ${Request} in a template or flowscript and have that be replaced 
with a reference to the correct object instance.

Is that clearer?

Ralph

Re: Accessors (was Re: Adding cocoon.suicide() to the FOM API.)

[Daniel Fagerstrom <da...@nada.kth.se>]

Ralph Goers wrote:

> Sylvain Wallez wrote:
>
>>>
>>>
>>> I can agree that it seem to break some common ideas about good 
>>> coding practice. But we have been through the arguments and it seem 
>>> OK. We probably find out if it works when we start to implement and 
>>> integrate it.
>>
>>
>>
>>
>> Oh yes, sure. I totally agree with the concept. It's not a factory 
>> and it's not an object holder as depending on the implementation it 
>> can be either or even something else. So accessor is fine!
>>
>> Sylvain
>
>
> Did this accessor thing evolve from another discussion?  It seemed to 
> pop up out of thin air in this thread.

It did, I had thought a little bit more about what to call them and 
wanted to tell, Sylvain decreased the confussion by changing the thread 
name.

> Is this what I hope it means?  If it is, then I hope to see classes 
> like Request, Session, Context, etc. be modified to implement the 
> interface.  To me, this would mean that they implement a static get 
> method that returns the appropriate instance of the object.  Perhaps a 
> better name for this would be Accessible.  I guess your plan is to 
> implement a separate Accessor class to do this instead?

I'm not geting what your aim at, could you tell a little bit about how 
you want to use the accessores so that I can understand why you prefer 
such a solution compared to the component based approach that we have 
discussed.

/Daniel

Re: Accessors (was Re: Adding cocoon.suicide() to the FOM API.)

[Ralph Goers <Ra...@dslextreme.com>]

Sylvain Wallez wrote:

>>
>>
>> I can agree that it seem to break some common ideas about good coding 
>> practice. But we have been through the arguments and it seem OK. We 
>> probably find out if it works when we start to implement and 
>> integrate it.
>
>
>
> Oh yes, sure. I totally agree with the concept. It's not a factory and 
> it's not an object holder as depending on the implementation it can be 
> either or even something else. So accessor is fine!
>
> Sylvain

Did this accessor thing evolve from another discussion?  It seemed to 
pop up out of thin air in this thread.

Is this what I hope it means?  If it is, then I hope to see classes like 
Request, Session, Context, etc. be modified to implement the interface.  
To me, this would mean that they implement a static get method that 
returns the appropriate instance of the object.  Perhaps a better name 
for this would be Accessible.  I guess your plan is to implement a 
separate Accessor class to do this instead?

Ralph