Two scoopsofdjango common patterns for forms

Two Scoops of Django
Chapter 9 Common Patterns for Forms

Alfred

Forms
This chapter goes explicitly into the
concepts of forms, models and CBVs. There
are ﬁve common patterns.

Pattern 1: Simple ModelForm
with default Validators

Pattern 1: Simple ModelForm
with default Validators

• Auto generated a model form based on the
Flavor model.

Pattern 2: Custom Form Field
Validators in ModelForm

Validators in ModelForm

• Customize your validator.

Validators in ModelForm(cont.)

• To use it

•what if we wanted to use validate_tasty() in just forms?

•what if we wanted to assign it to other ﬁelds?


• To create a customized form...
#forms.py
from django import forms
from core.validators import validate_tasty
from .models import Flavor

!
class FlavorForm(forms.ModelForm):
def __init__(self, *args, **kwargs):
super(FlavorForm, self).__init__(args, kwargs)
self.fields["title"].validators.append(validate_tasty)
self.fields["slug"].validators.append(validate_tasty)

!
class Meta:
model = Flavor

#views.py
from django.contrib import messages
from django.views.generic import CreateView, UpdateView, DetailView
from braces.views import LoginRequiredMixin
from .models import Flavor
from .forms import FlavorForm

!

class FlavorActionMixin(object):
model = Flavor
@property
def action(self):
msg = "{0} is missing action.".format(self.__class__)
raise NotImplementedError(msg)

!
!

def form_valid(self, form):
msg = "Flavor {0}!".format(self.action)
messages.info(self.request, msg)
return super(FlavorActionMixin, self).form_valid(form)

class FlavorCreateView(LoginRequiredMixin, FlavorActionMixin, CreateView):
model = Flavor
action = "created"
form_class = FlavorForm

!

class FlavorUpdatedView(LoginRequiredMixin, FlavorActionMixin, UpdateView):
model = Flavor
action = "updated"
form_class = FlavorForm

!

class FlavorDetailView(DetailView):
model = Flavor

Pattern 3: Overriding the clean
stage of Validation

stage of Validation

• Multi-field validation

• Validation involving existing data from the
database that has already been validated.

clean() and clean<field_name>()

•

clean() method is the place to validate two or more fields
against each other, since it’s not specific to any one particular
field.

•

The clean validation stage is a better place to attach validation
against persistent data.

stage of Validation(cont.)

• We are going to check the remaining amount
is enough or not...

class IceCreamOrderForm(forms.ModelForm):
slug = forms.ChoiceField("Flavor")
toppings = forms.CharField()

!
!

super(IceCreamOrderForm, self).__init__(*args, **kwargs)
self.fields["slug"].choices = [ (x.slug, x.title) for x in Flavor.objects.all() ]
def clean_slug(self):
slug = self.cleaned_data["slug"]
if Flavor.objects.get(slug=slug).scoops_remainin <= 0:
msg = u"sorry, we are out of flavor"
raise forms.ValidationError(msg)
return slug

stage of Validation(cont.)

• And then check multiple ﬁelds..
class IceCreamOrderForm(forms.ModelForm):
...
def clean(self):
cleaned_data = super(IceCreamOrderForm, self).clean()
slug = cleaned_data.get("slug", "")
toppings = cleaned_data.get("toppings", "")
if u"chocolate" in slug.lower() and u"chocolate" in toppings.lower():
msg = u"Your order has too much chocolate."
raise forms.ValidationError(msg)
return cleaned_data

Pattern 4: Hacking Form Fields

Pattern 4: Hacking Form Fields

• you have a ice cream store, some of ﬁelds
are required, some are not.

from django.db import models
from django.core.urlresolvers import reverse
# Create your models here.

!
class IceCreamStore(models.Model):
title = models.CharField(max_length=100)
block_address = models.TextField()
phone = models.CharField(max_length=20, blank=True)
description = models.TextField(blank=True)
def get_absolute_url(self):
return reverse("store_detail", kwargs={"pk":self.pk})

Pattern 4: Hacking Form
Fields(cont.)

• Old style v.s. better style

from models import IceCreamStore
class IceCreamStoreUpdateForm(forms.ModelForm):

!
phone = forms.CharField(required=True) #duplicate
description = forms.TextField(required=True) #duplicate

!
class Meta:
model = IceCreamStore
class IceCreamStoreUpdateForm(forms.ModelForm):

!
!

class Meta:
super(IceCreamStoreUpdateForm, self).__init__(*args, **kwargs)
self.fields["phone"].required=True
self.fields["description"].required=True

Fields(cont.)

• Much Better Style
from models import IceCreamStore

!

class IceCreamStoreCreateForm(forms.ModelForm):
class Meta:
field = ("title", "block_address", )

!

class IceCreamStoreUpdateForm(IceCreamStoreCreateForm):
super(IceCreamStoreUpdateForm, self).__init__(*args, **kwargs)
self.fields["phone"].required=True
self.fields["description"].required=True

!
!

class Meta:
fields = ("title", "block_address", "phone", "description")

Fields(cont.)

• Use it in view
from
from
from
from

django.views.generic import CreateView, UpdateView
forms import IceCreamStoreCreateForm
forms import IceCreamStoreUpdateForm
models import IceCreamStore

!
class IceCreamCreateView(CreateView):
model=IceCreamStore
form_class=IceCreamStoreCreateForm

!
class IceCreamUpdateView(UpdateView):
model=IceCreamStore
form_class=IceCreamStoreUpdateForm

Pattern 5: Reusable Searching
Mixin View

Pattern 5: Reusable Searching
Mixin View

• Use a simple search view on multiple models
class TitleSearchMixin(object):
def get_queryset(self):
queryset = super(TitleSearchMixin, self).get_queryset()

!

!

q = self.request.GET.get("q")
if q:
return queryset.filter(title__icontains=q)
return queryset
{#form go into store#}

class FlavorListView(TitleSearchMixin, ListView):
model = Flavor

!

class StoreListView(TitleSearchMixin, ListView):
model = Store

<form action="" method="GET">
<input type="text" name="q"/>
<button type="submit">search</
button>
</form>
{#form go into flavor#}
<form action="" method="GET">
<input type="text" name="q"/>
<button type="submit">search</
button>
</form>

Two scoopsofdjango common patterns for forms

More Related Content

What's hot (19)

Similar to Two scoopsofdjango common patterns for forms (20)

Recently uploaded (20)

Two scoopsofdjango common patterns for forms