[Zope3-dev] Re: Dependencie-handling

[R. David Murray]

On Tue, 1 Jul 2003, Marcus J. Ertl wrote:
> I think it isn't that easy! For example: For my forum I will need:
>
> A textsource service like used in zwiki! This must be installed
> earlier!
> A Membership System
> A Database Adapter
> A Service of my own, for creating unique names

My point is that you should not be depending on *specific* other
packages, but rather on Interfaces.

> Of course, if one is missing, an errormessage should be given. But I
> think there should be a common way for
>
> - checking for such depencies

Checking is straightforward: try to access the Interface your package
needs.  I don't think there is any more general way to do this,
nor should there be.

> - a commone way to tell the user/admin of them.

Good idea.  I'm not up-to-date on all the new X3 features, but I
don't think this is one of them.  Make a proposal <grin>.

> IMHO, there should be a standard way to tell an admin/user why
> something is broken. And in a not perfekt but good world, it also would
> tell admin/user what to do!

Once you test for the presence of the Interface you need, you can
trap the error, and return a message saying something like:
Can't find XXX service (or XXX component).  Installing package
YYY is one good way to solve this problem" <grin>.  At the very least
there should be a Best Practicies document that decribes how
to do this kind of checking.

> Just tell me, where should the message go to:
>
> - zmi

When instaling the package through the zmi, +1

> - stdout

-1

> - logfile

+1 (use the standard logging facility)

> - a special logfile

-1. But the package configuration/registration/whatever-it-is page should
probably have these error messages.

> - per mail to admin

-1

> And as long time project, a system like apt-get on debian would be fun,
> witch resolves such problems on it self.

Variations on this have been discussed, but I don't think anyone
has done any coding yet.

--RDM