Forms

Backend half of forms (there is also frontend part)

Definition: Django Form:

A Python class that defines field behavior and validation rules for user inputs.

Properties: Forms backend pieces

• forms.py: The standard location for form classes within a Django app.

• forms.ModelForm: Specialized form that maps directly to a Django Model.

• forms.Form: Standard form for inputs not tied to a database table.

Workflow: Adding a forms.ModelForm

1. Identify the Model requiring user input.

2. Open forms.py and import dependencies:

   from django import forms
   from .models import Book
   

3. Create the class with a Meta inner class:

   class BookForm(forms.ModelForm):
       class Meta:
           model = Book
           fields = ['title', 'author']
   

4. Define widgets for field-specific attributes (placeholders, rows, or AlpineJS attrs):

   widgets = {
       'text': forms.Textarea(attrs={
           'rows': 4, 
           'placeholder': 'Enter book description...'
       }),
       'published_date': forms.TextInput(attrs={
           'x-mask': '99/99/9999',
           'placeholder': 'MM/DD/YYYY'
       }),
   }
   

5. Use the form in views.py:

   @require_POST
   def update_book(request, pk):
       book = Book.objects.get(pk=pk)
       form = BookForm(request.POST or None, instance=book)
       if form.is_valid():
           form.save()
   

Properties: Fields

• forms.CharField - A field for string input:

  title = forms.CharField(
      max_length=200,
      widget=forms.Textarea(attrs={'rows': 4, 'cols': 40}),
      label="Book Title"
  )
  

• forms.DateTimeField - A field for date and time input:

  published_at = forms.DateTimeField(
      widget=forms.DateTimeInput(attrs={'type': 'datetime-local'}),
      initial=timezone.now,
      label="Publication Date"
  )
  

• forms.ModelChoiceField - A ChoiceField whose choices are a model QuerySet:

  author = forms.ModelChoiceField(
      queryset=Author.objects.all().order_by('name'),
      empty_label="Select an Author...",
      label="Author"
  )
  

• forms.ModelMultipleChoiceField - Allows selecting multiple instances:

  genres = forms.ModelMultipleChoiceField(
      queryset=Genre.objects.all(),
      widget=forms.CheckboxSelectMultiple,
      label="Genres"
  )
  

Workflow: Cleaning the data

1. Add method for field you want to clean

   def clean_field_name(self):
       self.field_name = self.field_name.upper()
   

2. Call full_clean() before saving the model