[Zope3-dev] Local Utility-Service and persistent Utilities

[Jim Fulton]

Ulrich Eck wrote:
> At several parts of my work (schedule, workflow) i needed persistent 
> Utilities
> so i decided to start work on them.
> 
> Before i can start i need some information about the way it should be done.
> 
> General structure:
> 
>  - A Local-UtilityService that is configured with the Service Manager
>  - A Component that is added to some package
>  - This Component is configured with the UtilityService
> 
> My Questions:
> 
>  1. What information is needed to configure a utility-component ?
>     My Guess:
>      - providedInterface (the interface the component provides or 
> choosen TTW)
>      - utilityName (an optional name)

Right.

>      - componentPath (the path to the utility-component)
>     so the Configuration key would be a tuple (providedInterface, 
> utilityName) ??

Right, but this is almost an implementation detail.
The Utility configuration object will use a component path
internally and provide a getComponent method to retrieve the
utility it configures.

>  2. What components can be configured as Utilities ?

Any object that provides the desired interface can be configured as
a utility.


>     When building the Configuration Screens i need to give a choice of 
> components
>     that can be configured as Utilities. How do i find out which one are 
> avaliable ??
>     afaik there is not common Interface for Utilities.

First (absent Javascript magic), get the user to select an interface,
then call queryComponent (see src/zope/app/interfaces/services/service.py)
on the service manager to find the components that provide that interface.

>  3. Should there be a possiblity to add persistently added 
> component-instances as well
>     as python-based (like global Utilities) ones ??

Yes, I thought that's what you were talking about, since components
created in modules don't have "paths".

>  4. How does resolving Utilities work when they have a name ?

getUtility(IFoo, name="spam")

>     from the sources it seems, that when a utility is provided with 
> name, it is not
>     found when one queries only for the interface it provides .. is this 
> behaviour
>     correct and wanted ??

Yes.

>   5. How is registration/configuration handled when:
>      - two utilities provide the same interface (no name) --> exclusive 
> activation.

Yes, only one can be active.

>      - two utilities provide same name and interface --> exclusive 
> activiation.

ditto

>      - one util provides interface - no name, other provides the same 
> interface with name ?

They are different utilities. There is no conflict.

>      - two utilities provide different interfaces for the same name ?

Ditto.

> I would basically start with adapter-service as template, add specific 
> configuration-code,
> use the ImplementorRegistry (made persistent) to store 
> Utility-configuration
> and build a TTW-Config-screen.

Right. Internally, you'll have a PersistentDict from utility name,
to ImplementorRegistry objects for each name.

> What else should i take care of when start working on this issue ??

You'll need a searching UI as in the adapter service.

This is not a small task. :)

If you need this for workflow, I'd be willing to do it for you so
you can focus on workflow.

> thanks for your comments

You're welcome.

Jim

-- 
Jim Fulton           mailto:jim@zope.com       Python Powered!
CTO                  (888) 344-4332            http://www.python.org
Zope Corporation     http://www.zope.com       http://www.zope.org