Handling Checkbox Input for a DateTimeField in Django

The issue you're encountering is due to a mismatch between your field type (DateTimeField) and the widget you're using (CheckboxInput). A checkbox returns a boolean value, but a DateTimeField expects a datetime string or object.

The Problem

You're trying to use a checkbox to set a timestamp, but Django's form processing pipeline can't convert a boolean to a datetime automatically. The error occurs because the DateTimeField tries to call .strip() on the boolean value returned by the checkbox.

Solution Options

Option 1: Use a BooleanField in the Form (Recommended)

Create a separate boolean field in your form (not the model) to handle the checkbox, then override the save() method to set the datetime:

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class TaskForm(ModelForm):
    is_completed = forms.BooleanField(required=False, label="Completed")
    
    class Meta:
        model = Task
        fields = ["text", "private", "deadline", "scheduled", "deleted"]  # Remove completed
        # Remove the completed widget from here
    
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        # Initialize the checkbox based on whether completed has a value
        if self.instance.pk and self.instance.completed is not None:
            self.fields['is_completed'].initial = True
    
    def save(self, commit=True):
        instance = super().save(commit=False)
        
        # Set completed datetime based on checkbox
        if self.cleaned_data.get('is_completed'):
            if instance.completed is None:  # Only update if not already completed
                instance.completed = timezone.now()
        else:
            instance.completed = None
            
        if commit:
            instance.save()
        return instance

Option 2: Use a Hidden Field for the Actual DateTime

Another approach is to keep the completed field in your form but make it hidden, and use a separate checkbox to control it:

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from django.utils import timezone

class TaskForm(ModelForm):
    mark_completed = forms.BooleanField(required=False, label="Completed")
    
    class Meta:
        model = Task
        fields = ["completed", "text", "private", "deadline", "scheduled", "deleted"]
        widgets = {
            "completed": forms.HiddenInput(),
            # other widgets...
        }
    
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        # Initialize checkbox based on completed field
        self.fields['mark_completed'].initial = self.instance.completed is not None
    
    def clean(self):
        cleaned_data = super().clean()
        mark_completed = cleaned_data.get('mark_completed')
        
        if mark_completed and not cleaned_data.get('completed'):
            # Set to current time if checked and not already set
            cleaned_data['completed'] = timezone.now()
        elif not mark_completed:
            # Clear the datetime if unchecked
            cleaned_data['completed'] = None
            
        return cleaned_data

Option 3: Fix Your Model

Your model has an issue - the default=False for a DateTimeField is incorrect. It should be either None or a datetime:

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class Task(models.Model):
    ...
    completed = models.DateTimeField(
        null=True, blank=True, default=None  # Changed from False to None
    )
    ...

Recommendation

I recommend Option 1 as it provides the cleanest separation of concerns. The form handles the user interaction (checkbox) while properly managing the model's datetime field.

Remember to import timezone from django.utils to ensure you're using the correct timezone-aware datetime objects.