[python-uk] hexagonal Django

[Harry Percival]

This may be getting tenuous, but here's another example of  what I think of
as a "no-business-logic" app, and how we test-drove it:

http://www.obeythetestinggoat.com/test-driving-a-docker-based-postgres-service-using-pytest.html

Part of my blockage may come from the words "business logic" -- we don't
have much in the way of "business rules" here, so maybe Brandon's
definition -- business logic is all the stuff that can be expressed in
purely functional terms, with no side-effects -- could help me... But even
using that, so far all I've got is that we generate some paths on disks by
concatenating some strings together with some constants, so that's really
clutching at straws...

On 15 August 2014 17:01, Jonathan Hartley <tartley at tartley.com> wrote:

>  I think what you describe is a common situation. When I reorganised that
> application in a Django project, that was one aspect that bugged some of my
> coworkers.
>
> But I think there is potentially still some value there. The resulting one
> line business functions create a well-defined seam between your app's
> (slender) business logic and each of your interfaces to  external systems.
> That way, you make it easy for developers to avoid accidentally mixing
> 'django' code into the same module as code which talks to ElasticSearch.
>
> If you already have the discipline to maintain great separation of
> concerns (along these or other lines), which I'm guessing PythonAnywhere
> still does, then perhaps you don't need this particular constraint to help
> you maintain it.
>
> Is there also value in helping you plug in fake external services for
> testing purposes? I believe there is, but again, I'm not sure this value is
> greater than zero if you *already* have well thought-out mechanisms for
> plugging in fake external systems.
>
>     Jonathan
>
>
>
>
>
> On 15/08/14 11:22, Harry Percival wrote:
>
> Thanks Peter!  I was speaking to Brandon at Pycon this year and he was
> telling me this was going to be his next talk to take on the road, and I
> was definitely looking forward to seeing it.  Matt O'Donnell was also
> there, and he's done a talk on this sort of thing recently too (https://www.youtube.com/watch?v=NGhL7IA6Dik). It's definitely in the air.
>
> My own modest attempts to approach the subject are in my book -- in chapter
> 19, where I show how striving for test isolation can (theoretically) push
> you towards something like a lean architecture (http://chimera.labs.oreilly.com/books/1234000000754/ch19.html) and in
> chapter 21, the wrap-up, where I waffle on about all these things (http://chimera.labs.oreilly.com/books/1234000000754/ch22.html)
>
> I don't think I managed to broach the subject nearly as cleanly as Brandon
> did.  I really admire his talks.  His data structures talk was one of the
> top 3 I saw at Pycon this year (http://pyvideo.org/video/2571/all-your-ducks-in-a-row-data-structures-in-the-s).
> Perfect pace, slides that complement rather than repeat the talk,
> fascinating and useful content...
>
> Anyways, back to our onions - I guess the thing that's always bothered me a
> bit about the "clean architecture" is that my main project (pythonanywhere)
> is "all boundaries", to use Gary Bernhardt's terminology.  Or, to put it
> differently, I don't think we really have much in the way of "business
> logic".  We just turn Http requests into commands that go to processes.
> There's really not much in the way of "logic" in the way.  No calculations
> or business rules to speak of.  So it's never seemed worth it, to us.
>
> And sometimes I think -- aren't many web projects just thin CRUD wrappers
> around a database?  Is going to all the trouble of isolating your business
> logic from, eg, django, really worth it in most cases?
>
>
>
>
> On 13 August 2014 13:09, Daniel Pope <lord.mauve at gmail.com> <lord.mauve at gmail.com> wrote:
>
>
>  Coincidentally, I blogged on the topic of Django project organisation at
> the weekend.
> http://mauveweb.co.uk/posts/2014/08/organising-django-projects.html
>
> May be of interest?
>
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>
> --
> Jonathan Hartley    tartley at tartley.com    http://tartley.com
> Made of meat.       +44 7737 062 225       twitter/skype: tartley
>
>
>
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-- 
------------------------------
Harry J.W. Percival
------------------------------
Twitter: @hjwp
Mobile:  +44 (0) 78877 02511
Skype:         harry.percival
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