On Fri, Jan 8, 2016 at 12:55 AM, Torsten Irländer <tors...@irlaender.de> wrote:
> But I wasn't aware of that
> this
> could be a topic for a talk. Actually I thought this is kind of a hack but
> is
> seems to be not bad :D.

Organizing business logic has been a perennial issue for Pyramid and
Pylons developers forever. I started with high-level class methods and
instance methods in the ORM classes (depending on whether it's
operating on a single record or querying multiple ones), but I did all
the updating in the views. That led to two problems: the model modules
became large and cumbersome, and the views had so many unrelated
things intertwined. For the model problem I first extracted the
searching routines to separate classes in the model (SomethingQuery

Another thing I've long disliked was mixing presentation code and data
code in the views (Pylons controllers). The only choice was to put
formatting code in the Mako templates, and then if there's an
exception the traceback was often too generic and wouldn't tell you
where, or in the views with other stuff. Again I went maximum-template
approach, then minimum-template (a la mustache), then in between.

Later I was inspired by Mike Merickel's pyramid_services and the
Model-View-Presenter [1] paradigm. I tried pyramid_services but
couldn't find a good reason for adding the complication of the
registry class-matching stuff. So I ended up making my own service
classes that the views instantiate directly. The services handle
business logic, and the views focus mostly on Pyramid interaction
(form input, rendering variables).

I try to keep Pyramid-specific and presentation-specific things out of
the services, with three minor exceptions. One, services have a
'from_request' class method that extracts their data from the request
(e.g., database sessions using reified properties, engines using
"global" registry attributes). Two, they sometimes raise an
HTTPException if the caller would just do that anyway. I figure unit
tests can deal with an HTTPException as easily as some other
exception. Three, I sometimes have model methods or service methods
return a presentation-friendly value (JSONable dict, formatted string)
to avoid duplication and put the formatter close to the data fields.

[1] https://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93presenter

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