Python 通过外键Django创建从一个字段到其他字段的 Select 列表

选项1:只有Service个已经存在，您想要创建一个完整的新Reservation，并让用户 Select Connected Service.这个选项的答案很可能在后端Django中找不到，但必须在前端处理.原因是当用户 Select 不同的连接Service时，它需要在运行中切换turn的可能 Select .

选项2:当要求用户 Select turn时，具有连接Service的初始Reservation对象已经存在.Django 可以做到这一点.但不是在Models.py级别上.这一逻辑必须适用于forms.py.我们需要一个模型表单，只需要填充turn字段.

class ReservationForm(forms.ModelForm):
    class Meta:
        model = Reservation
        fields = ['turn']
        widgets = {
            'turn': forms.Select(),  # Set the widget for the 'turn' field to Select
        }

    def __init__(self, *args, **kwargs):
        service_instance = kwargs.pop('service_instance', None)
        super(ReservationForm, self).__init__(*args, **kwargs)

        if service_instance:
            # Set the choices for the 'turn' field based on the service instance's counter
            self.fields['turn'].choices = [(i, i) for i in range(service_instance.counter + 1)]
        else:
            # If no service instance is provided, default to an empty list
            self.fields['turn'].choices = []


# views.py
service_instance = Service.objects.get(id=service_id)
form = ReservationForm(service_instance=service_instance)

上面展示了如何创建动态表单.基本上，您是在视图中预先 Select 要传递给表单的内容.然后在__init__方法中，您可以捕获它并相应地设置它.

由于您说此表单始终已绑定到对象，因此已连接到服务，因此您也可以 Select 此选项:

class ReservationForm(forms.ModelForm):
    class Meta:
        model = Reservation
        fields = ['turn']
        widgets = {
            'turn': forms.Select(),  # Set the widget for the 'turn' field to Select
        }

    def __init__(self, *args, **kwargs):
        super(ReservationForm, self).__init__(*args, **kwargs)
        # next line checks if an object is already connected to the form and a service connected
        service_id = self.data.get('service') if self.is_bound else None

        if service_id:
            try:
                service_instance = Service.objects.get(id=service_id)
                # Set the choices for the 'turn' field based on the service instance's counter
                self.fields['turn'].choices = [(i, i) for i in range(service_instance.counter + 1)]
            except Service.DoesNotExist:
                # If the service does not exist, default to an empty list
                self.fields['turn'].choices = []
        else:
            # If no service ID is provided, default to an empty list
            self.fields['turn'].choices = []

# views.py
# here you need to pass an instance to the form
form = ReservationForm(request.POST, instance=Reservation.objects.get(id=1)