How to write a view

David Winterbottom slides - https://speakerdeck.com/codeinthehole/how-to-write-a-view

Views give you a lot of freedom - can lead to WTF moments

Separation of concerns

• Have layers only concerned with one thing
• see also SRP - single responsibility principle
• MVC - model view controller - originally GUI, now used in web frameworks, some parts moving into the browser
• Model layer - data, business logic (the rules, aka domain logic)
• View layer - what is presented to the user
• Controller - takes in request, orchestrates model interactions, passes stuff to view
• Django - MTV - Model, Template, View - see Django FAQ
• template is roughly equivalent to view
• view is roughly equivalent to controller
• so model -> models, forms
• view -> templates, statics
• controller -> django view, user, requests, responses

What is a view

• HTTP requests into domain request, do work, translate into HTTP response

Problem

• django views are too big
  • separation of concerns is broken
  • business logic, validation done in views
  • persistence logic - start/end transaction, even SQL queries
  • persentation layer - some work done in the view
• Django does blur the layers a bit
  • models mix business logic and persistence
  • modelforms and generic CBVs mix up stuff
  • fine most of the time, enormously productive, but need to be aware of the boundaries, and sometimes step back and separate things out
• MODEL != models.py
  • moving logic so you have thin views and fat models, but that puts too much in models
  • MODEL = domain/models.py domain/forms.py domain/services.py
  • don’t try and force everything into your model
  • though “service” is an over-used word

from ..service.service import Service

service = Service()

• too much!! - keep it simple - simple functions are fine if they work

view smells

• pass request/response to a domain function
• validation logic
• manipulate or saving models
  • article - tom christie, dab apps - http://dabapps.com/blog/django-models-and-encapsulation/
  • any change to model, write a different function, maybe put it in model layer
• sending email, access network ...

generic CBVs

• can bend them too much

Keep views boring

• don’t do anything interesting
• HTTP <-> domain