django-commands (For Git Bash in Windows)

Django 101

• Django is web framework provides a generic functionality needed for building:
  • web applications
  • APIs
  • web services
• Django used MVT Architecture mvtArchitecture
  • URL dispatcher
    • equivalent to the controller in the MVC architecture.
    • The URL patterns defined in each app under the project are also included, urls.py:

      from django.urls import path 
      from . import views 
      
      urlpatterns = [ 
          path('', views.index, name='index'), 
      ] 

  • View
    • view function reads the path, query, and body parameters included in the client's request If required.
      • It uses this data to interact with the models to perform CRUD operations.
    • A view can be a user-defined function or a class, You create View definitions in the views.pyfile of the respective app package folder.
    • The following code in the view.py file defines the index() view function.

      from django.shortcuts import render 
      # Create your views here. 
      from django.http import HttpResponse 
      
      def index(request): 
          return HttpResponse("Hello, world.") 

  • Model
    • a Python class, An app may have one or more model classes, conventionally put in the models.py file.
    • Django migrates the attributes of the model class to construct a database table of a matching structure.
    • Django's Object Relational Mapper helps perform CRUD operations in an object-oriented way instead of invoking SQL queries.
    • The view uses the client's and the model's data and renders its response using a template.
  • Template
    • a web page containing a mix of static HTML and Django Template Language code blocks.
    • You place Template web pages in the templates folder with the .html extension.
    • Django's template processor uses any context data from the view inserted in these blocks to formulate a dynamic response.
    • The view, in turn, returns the response to the user.
  • Django Documentation

create python venv

1. Make sure to have python installed, and update pip version

   py -m pip install --upgrade pip

2. Create a directory and in the directory create a python venv:

   mkdir <directory_name>

   cd <directory_name>

   py -m venv <env_name>

3. To activate venv

   source ./<env_name>/Scripts/activate

4. To deactivate venv

   deactivate

Install django library

1. In the directory, install django with pip

   pip install django

2. To check installed django version

   python -m django version

   or

   pip list

Create a django project

• In the directory, while venv has activated, run:

    django-admin startproject <project_name>

Create a django app

• In the directory, while venv has activated, run:

•   cd <project_name>

    python manage.py startapp <app_name>

Launch development server

1. In the directory while venv has activated, run:

  cd <project_name> 

   python manage.py runserver 

2. If the bash responded with:

Watching for file changes with StatReloader

• This mean server successfully launched. You can now open localhost. By default, the development server will be accessible at http://127.0.0.1:8000/ or http://localhost:8000/.

3. To stop development server, just hit ctrl+c in bash.

Creating a view and URL configuration

1. make sure to have django installed
2. in the views.py

     from django.shortcuts import render
     from django.http import HttpResponse
     def home(request):
         return HttpResponse("Hello World!")

3. in the App-level urls.py(If not exists please create one.)

    from django.urls import path
    from . import views
    urlpatterns = [
            path('', views.home, name="home"),
    ] 

4. in the Project-level urls.py

     from django.contrib import admin
     from django.urls import path, include
     
     urlpatterns = [
         path('admin/', admin.site.urls),
         path('', include('myapp.urls')),
     ] 

5. in the setting.py
   • add "'myapp.apps.MyappConfig'," to the INSTALLED_APPS list.

     INSTALLED_APPS = [        
         'django.contrib.admin',
         'django.contrib.auth',
         'django.contrib.contenttypes',
         'django.contrib.sessions',
         'django.contrib.messages',
         'django.contrib.staticfiles',
         'myapp.apps.MyappConfig', 
    ]

Create URL path with views HttpResponse

1. make sure to have django installed
2. in the views.py

     from django.shortcuts import render
     from http.client import HTTPResponse
     from django.http import HttpResponse
     
     def drinks(request, drink_name):
         drink = {
             'mocha' : 'type of coffee',
             'tea' : 'type of hot beverage',
             'lemonade': 'type of refreshment'
         }
         choice_of_drink = drink[drink_name]
         return HttpResponse(f"<h2>{drink_name}</h2> " + choice_of_drink)

3. in the App-level urls.py (If not exists please create one)

     from django.urls import path
     from . import views
     
     urlpatterns = [
         path('drinks/<str:drink_name>', views.drinks, name="drink_name"), 
     ]

App-level urls.py namespace

1. using instance namespace (If use this please skip step 2 - 4)
   • in Project-level urls.py

       #in demoproject/urls.py 
       urlpatterns=[ 
           # ... 
           path('demo/', include('demoapp.urls', namespace='demoapp')), 
           # ... 
       ] 

2. adding "app_name = <app_name>" to App-level urls.py

  #demoapp/urls.py
  from django.urls import path  
  from . import views    
  app_name='demoapp' 
  urlpatterns = [  
      path('', views.index, name='index'),      
  ] 

3. we can also use namespace with more than one app

  #newapp/urls.py 
 from django.urls import path 
 from . import views 
 app_name='newapp' 
 urlpatterns = [ 
     path('', views.index, name='index'), 
 ] 

4. In the Project-level urls.py

  from django.contrib import admin 
  from django.urls import path, include 
  
  urlpatterns = [ 
      path('admin/', admin.site.urls), 
      path('demo/', include('demoapp.urls')), 
      path('newdemo/', include('newapp.urls')), 
  ] 

5. To check the url path/route in django shell

  python manage.py shell 

  >>> reverse('demoapp:index') 
  '/demo/' 

  >>> reverse('newapp:index') 
  '/newdemo/' 

6. In views.py

    from django.http import HttpResponsePermanentRedirect 
    from django.urls import reverse 
      
    def myview(request): 
        .... 
        return HttpResponsePermanentRedirect(reverse('demoapp:login'))

7. Using namespace in the url tag

• without using namespace

   <form action="/demoapp/login" method="post"> 
   #form attributes 
   <input type='submit'> 
   </form> 

   <form action="{% url 'login' %}" method="post"> 
   #form attributes 
   <input type='submit'> 
   </form> 

• using namespace

   <form action="{% url 'demoapp:login' %}" method="post"> 
   #form attributes 
   <input type='submit'> 
   </form> 

views.py Http Error Handling

• Basic error handling (in views.py)

  from django.http import HttpResponse, HttpResponseNotFound 
  def my_view(request): 
      # ... 
      if condition==True: 
          return HttpResponseNotFound('<h1>Page not found</h1>') 
      else: 
          return HttpResponse('<h1>Page was found</h1>') 

  or

   from django.http import HttpResponse 
   def my_view(request): 
       # ... 
       if condition==True: 
           return HttpResponse('<h1>Page not found</h1>', status_code='404') 
       else: 
           return HttpResponse('<h1>Page was found</h1>') 

• Raise error handling (in views.py)

  from django.http import Http404, HttpResponse 
  from .models import Product 
  
  def detail(request, id): 
      try: 
          p = Product.objects.get(pk=id) 
      except Product.DoesNotExist: 
          raise Http404("Product does not exist") 
      return HttpResponse("Product Found") 

  • Custom page error handling (in views.py)
    1. First in settings.py set DEBUG to FALSE and add '*' to the ALLOWED_HOSTS to include all possible hosts.

       #settings.py      
       # SECURITY WARNING: don't run with debug turned on in production!        
       DEBUG=FALSE
       ALLOWED_HOSTS = ['*']

    2. ...
  • Exception Classes
    • ObjectDoesNotExist: All the exceptions of the DoesNotExist are inherited from this base exception.
    • EmptyResultSet: This exception is raised if a query does not return any result.
    • FieldDoesNotExist: This exception is raised when the requested field does not exist.

      try: 
         field = model._meta.get_field(field_name) 
      except FieldDoesNotExist: 
         return HttpResponse("Field Does not exist") 

    • MultipleObjectsReturned: When you expect a certain query to return only a single object, however multiple objects are returned. This is when you need to raise this exception.
    • PermissionDenied: This exception is raised when a user does not have permission to perform the action requested.

      def myview(request): 
          if not request.user.has_perm('myapp.view_mymodel'): 
              raise PermissionDenied() 
          return HttpResponse() 

    • ViewDoesNotExist: This exception is raised by django.urls when a requested view does not exist, possibly because of incorrect mapping defined in the URLconf.
    • Django’s Form API

      def myview(request):   
          if request.method == "POST":   
              form = MyForm(request.POST)   
              if form.is_valid():   
                  #process the form data 
              else:   
                      return HttpResponse("Form submitted with invalid data")