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Django - Class-based views

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• Django - Class-based views
  • Class-based View
  • Usage of generic views
    • Example: View
  • Handling forms
  • Decorating class-based views
    • Decorating in URLconf
    • Decorating the class
  • CRUD
    • Example: CRUD
      • Create
      • Detail
      • Update
      • Delete

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Class-based View

• view:
  • a callable which takes a request and returns a response.

• Django provides base view classes and all views inherit from the View class, which handles linking the view into the URLs, HTTP method dispatching and other common features.

• RedirectView provides a HTTP redirect.
• TemplateView extends the base class to make it also render a template.

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Usage of generic views

1. Passing pass attributes into the as_view() method when the view is called in URLconf.
   • It will override attributes set on the class.

   # urls.py
   from django.urls import path
   from django.views.generic import TemplateView   # calling generic TemplateView
   
   urlpatterns = [
       path("about/", TemplateView.as_view(template_name="about.html")),   # passing attributes
   ]
   

2. Inheriting from an existing view and override attributes or methods. Then add as_view() when called in URLconf

   # some_app/views.py
   from django.views.generic import TemplateView
   
   class AboutView(TemplateView):
       template_name = "about.html"     # overriding template_name attribute
   

   # urls.py
   from django.urls import path
   from some_app.views import AboutView
   
   urlpatterns = [
       path("about/", AboutView.as_view()),     
   ]
   

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Example: View

# views.py
from django.http import HttpResponse
from django.views import View


class GreetingView(View):
    greeting = "Good Day"       # create an attribute
    
    # define get method to handle HTTP GET
    # identical to:
    # if request.method == "GET":
    #     return HttpResponse("result")
    def get(self, request):     
        return HttpResponse(self.greeting)


# urls.py
from django.urls import path
from myapp.views import MyView

urlpatterns = [
    path("about/", GreetingView.as_view(greeting="G'day")),
]

---

Handling forms

• Using function-based view

from django.http import HttpResponseRedirect
from django.shortcuts import render

from .forms import MyForm


def myview(request):
    if request.method == "POST":
        form = MyForm(request.POST)
        if form.is_valid():
            # <process form cleaned data>
            return HttpResponseRedirect("/success/")
    else:
        form = MyForm(initial={"key": "value"})

    return render(request, "form_template.html", {"form": form})

• Using class-based view

from django.http import HttpResponseRedirect
from django.shortcuts import render
from django.views import View

from .forms import MyForm       # import a cutomized form class


class MyFormView(View):
    form_class = MyForm     # assign form class
    initial = {"key": "value"}      # define initial for form class
    template_name = "form_template.html"    # define template for render

    # define a get method
    def get(self, request, *args, **kwargs):
        form = self.form_class(initial=self.initial)
        return render(request, self.template_name, {"form": form})

    # define a post method
    def post(self, request, *args, **kwargs):
        form = self.form_class(request.POST)
        if form.is_valid():
            # <process form cleaned data>
            return HttpResponseRedirect("/success/")

        return render(request, self.template_name, {"form": form})

---

Decorating class-based views

Decorating in URLconf

• Example:

from django.contrib.auth.decorators import login_required, permission_required
from django.views.generic import TemplateView

from .views import VoteView

urlpatterns = [
    path("about/", login_required(TemplateView.as_view(template_name="secret.html"))),
    path("vote/", permission_required("polls.can_vote")(VoteView.as_view())),
]

---

Decorating the class

• The class definition need to be decorated, using method_decorator decorator.
  • apply the decorator to the dispatch() method of the class.
• Example:

1. Decorate the dispatch method

   from django.contrib.auth.decorators import login_required
   from django.utils.decorators import method_decorator
   from django.views.generic import TemplateView
   
   
   class ProtectedView(TemplateView):
       template_name = "secret.html"
   
       @method_decorator(login_required)   # decorating the dispatch method
       def dispatch(self, *args, **kwargs):
           return super().dispatch(*args, **kwargs)
   

2. Decorate the class

   @method_decorator(login_required, name="dispatch")
   class ProtectedView(TemplateView):
       template_name = "secret.html"
   

3. Multiple Decorators

    decorators = [never_cache, login_required]
   
    @method_decorator(decorators, name="dispatch")
    class ProtectedView(TemplateView):
        template_name = "secret.html"
   
    @method_decorator(never_cache, name="dispatch")
    @method_decorator(login_required, name="dispatch")
    class ProtectedView(TemplateView):
        template_name = "secret.html"
   

---

CRUD

• CRUD:
  • stands for Create Retrieve Update Delete
• Django provides Class-base Views for CRUD:
  • CreateView
  • UpdateView
  • DeleteView

---

Example: CRUD

Create

• views.py

class CompanyCreateView(CreateView):
    model = Company

    # fields attribute: A list of names of fields.
    fields = ["name",]

    # "template_name" attribute: The full name of a template
    #       Default: "app/model_form.html"
    # template_name = "CBVApp/com_add.html"
    
    # "success_url" attribute: The URL to redirect to when the form is successfully processed.
    # Default: the url set in model's get_absolute_url()

• urls.py

app_name = "CBVApp"

urlpatterns = [
    # some urls
    path('create/', view=CompanyCreateView.as_view(), name="com_create"),
    # some urls
    ]

• templates: entry

<a href="-/ url 'CBVApp:com_create' \-">Add New Company</a>

• templates: form

-/ extends "layout/base.html" \- 
-/ block main \-
<h1>
  -/ if not form.instance.pk \- 
    Create Company 
  -/ else \- 
    Update Company 
  -/ endif \-
</h1>
<form method="post">
  -/ csrf_token \-
  --form.as_div--
  <button type="submit">
    Submit
  </button>
</form>
-/ endblock \-

---

Detail

• views.py

class CompaneyDetailView(DetailView):
    model = Company

    # "context_object_name" attribute:  the name of the list object in the context
    #       Default: "model_detail"
    context_object_name = "company_info"
    template_name = "CBVApp/com_info.html"

• urls.py

app_name = "CBVApp"

urlpatterns = [
    # DetailView requires pk as argument
    path('?<int:pk>/', view=CompaneyDetailView.as_view(), name="com_info"),
]

• template: entry

<a href="--company.get_absolute_url--"> --company.name-- </a>

• template: form

-/ extends "layout/base.html" \- 
-/ block main \-

<h1>Company Detail</h1>

-/ if not company_info \-
    <p>No Company Data</p>
-/ else \-
    <p><b>Company Name</b>--company_info--</p>

    <h2>Employees</h2>
    -/ if not company_info.employees \-
        <p>No Employee Data</p>
    -/ else \-

      <ul>
      -/ for emp in company_info.employees.all \-
        <li>--emp--</li>
      -/ endfor \-
      </ul>

    -/ endif \-


    <a href="-/ url 'CBVApp:com_list' \-">Back</a>
    <a href="-/ url 'CBVApp:com_update' pk=company_info.pk \-">Update</a>
    <a href="-/ url 'CBVApp:com_delete' pk=company_info.pk \-">Delete</a>
-/ endif \- 

-/ endblock \-

---

Update

• views.py

class CompanyUpdateView(UpdateView):
    model = Company
    fields = ["name",]

    # "template_name" attribute: The full name of a template
    #       Default: "app/model_form.html"

    # "success_url" attribute: The URL to redirect to when the form is successfully processed.
    # Default: the url set in model's get_absolute_url()

• urls.py

urlpatterns = [
    # UpdateView requires pk as argument
    path('update/<int:pk>', view=CompanyUpdateView.as_view(), name="com_update"),
]

• template: entry

<a href="-/ url 'CBVApp:com_update' pk=company_info.pk \-">Update</a>

• template: form
  • reuse create form

---

Delete

• views.py

class CompanyDeleteView(DeleteView):
    model = Company

    # "success_url" attribute: The URL to redirect to when the form is successfully processed.
    #   Default: For deletion, it usually redirects to the list url
    success_url = reverse_lazy("CBVApp:com_list")

• urls.py

urlpatterns = [
    # DeleteView requires pk as argument
    path('delete/<int:pk>', view=CompanyDeleteView.as_view(), name="com_delete"),
]

• template: entry

<a href="-/ url 'CBVApp:com_delete' pk=company_info.pk \-">Delete</a>

• template: form

-/ extends "layout/base.html" \- 

-/ block main \-
<h1>Delete --company.name--?</h1>
<form method="post">
  -/ csrf_token \- 
  --form.as_div--
  <a class="btn btn-secondary" href="-/ url 'CBVApp:com_info' pk=company.pk \-">Cancel</a>
  <button class="btn btn-danger" type="submit">Delete</button>
</form>

-/ endblock \-

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