[Zope-dev] Re: ZPatterns, ObjectDomain, UML and all that.....

[Itai Tavor]

There might be many ways to implement each connection, but I think 
that there will always be one or two ways that would be simplest and 
most robust... so this would not only save you the trouble of 
figuring it out alone every time, but would also prevent you from 
getting stuck down the road.

The problem is that we have at best guesses, and at worst empty table 
cells in the guide. I'm still struggling with many of these... The 
worst one seems to be XOR type connections, where a Specialist 
implementing a role is not involved. Example:

Actor: Person.

Participants: Customer, Reseller

Object connections:     (Customer)  1-------[XOR A] 1  (Actor)  [XOR 
A] 1-------1  (Reseller)

acl_users Login Manager authenticates users using Actor objects (by 
connecting the the Actors Specialist). The application needs to 
identify the Participant.

If you add participant_id to Actor, you still don't know which 
Participant Specialist to load the Participant from. You don't want 
to add participant_type to Actor (at least, I don't think you do - it 
seems real ugly). So, what do you do? Do you place the Customers and 
Resellers Specialists inside a Participants Specialist? We'll have to 
call it MegaSpecialist :-). Bad idea - other parts of the application 
have to access Resellers specifically, so Resellers should not be 
hidden inside the MegaSpecialist. So, do you create a Participants 
Specialist with virtual Racks for Customers and Resellers? What, 
another Specialist just to link Actors to Participants? Will this 
never end :-(?

See, I'm stuck. Please please please could someone who do not 
identify themselves as ZPatterns novices find the time to add to this 
guide?


Steve Spicklemire wrote:

>	I think this is a brilliant idea! I'm sure there are sixteen
>ways to implement each of these... but having one concrete way would
>be a big help to a novice.... 
>
>-steve
>
>>
>>
>>     Object relationship    |  
>>          (Pattern)         |  Implementation
>> 
>>----------------------------------------------------------------------------------------
>>        1       1           | Add prop to A: b_id
>>      A --------- B         | In A call Bs (Specialist of B): my_b =
>>  Bs.getItem(b_id)
>> 
>>----------------------------------------------------------------------------------------
>>        n       1           | Add prop to B: a_id
>>      A --------- B         | Add method to Bs (Specialist of B): 
>>getBsForA(a_id)
>>                            | In A call Bs: my_b_list = Bs.getBsForA(a_id)
>> 
>>----------------------------------------------------------------------------------------
>>        n       n           | ?
>>      A --------- B         |
>> 
>>----------------------------------------------------------------------------------------
>>       n   [XOR A] 1        | Add Specialist Xs implementing role of A and B
>>    A  -------------        | Add prop to C: x_id
>>       n   [XOR A] 1  C     | In A, B call Xs: my_x = Xs.getItem(x_id)
>>    B --------------        |
>>  (Participant-Transaction)| (A and B - Participants, C - Transaction)
>> 
>>----------------------------------------------------------------------------------------
>>      [XOR A] 1  n          | Add prop to B, C: a_id
>>      ------------ B        | In B, C call As (Specialist of A): my_a =
>>  As.getItem(a_id)
>>    A [XOR A] 1  n          |
>>      ------------ C        | (can't do reverse connection?)
>> 
>>----------------------------------------------------------------------------------------
>>
>>
>>  Does anyone think this would be useful? Can we get the experts to
>>  expand/correct/verify this? Obviously more relationship types need to
>>  be added, and also some extra information is needed (such as who's
>>  responsible to set the id attributes and how, when and how reverse
>>  connections are done, etc.).
>>
>  > Itai
-- 
Itai Tavor                    "Je sautille, donc je suis."
C3Works    itai@c3works.com              - Kermit the Frog

"If you haven't got your health, you haven't got anything"