在Django表单中将CharField动态转换为ChoiceField吗？

Question

In Django, How can I convert a field from CharField to ChoiceField dynamically? Could you please help me to fix the below traceback error?

For example,

This is my below model:

class Clients(models.Model):
    #senegal
    city_order = models.CharField(max_length=40, null=True, verbose_name='City Orderform')
    email = models.EmailField(verbose_name='Email Address')
    duration = models.CharField(max_length=100, blank=True, null=True, verbose_name="Duration")

Note: fields_for_model is used to fetch the fields.

ModelForm: from django.forms.models import fields_for_model

class Argentina(forms.ModelForm):
    class Meta:
        model = Clients
        fields = ['duration', 'email']  

    def __init__(self, *args, **kwargs):
        city = kwargs.pop('city_order')
        super(Argentina, self).__init__(*args, **kwargs)

        if city.lower() == 'senegal':
           #Changing the fields dynamically based on the city
           _fields = ['duration']
           self.fields = fields_for_model(Clients, _fields)
           #here the type of the field need to be changed to choicefield from charfield which is default by model definition.
           self.fields['duration']  = forms.ChoiceField(choices = (('Sample', 'Testing')), label="Duration")

This field type will be changed based on the explicit attribute city .The fields are created dynamically and field type also has to be changed as defined in the ModelForm called Argentinal above.

Traceback: I get ValueError in Django Template. Too many values to unpack .

Django Version: 1.6.6
Python Version: 2.7.8
Installed Applications:
('django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'bootstrapform',
 'orders')
Installed Middleware:
('django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware')


Traceback:
File "/usr/lib/python2.7/dist-packages/django/core/handlers/base.py" in get_response
  112.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/home/nava/ws/vbservices/vbservices/orders/views.py" in ordersubmission
  88.         print "form",form
File "/usr/lib/python2.7/dist-packages/django/utils/encoding.py" in <lambda>
  60.         klass.__str__ = lambda self: self.__unicode__().encode('utf-8')
File "/usr/lib/python2.7/dist-packages/django/forms/forms.py" in __str__
  103.         return self.as_table()
File "/usr/lib/python2.7/dist-packages/django/forms/forms.py" in as_table
  223.             errors_on_separate_row = False)
File "/usr/lib/python2.7/dist-packages/django/forms/forms.py" in _html_output
  186.                     'field': six.text_type(bf),
File "/usr/lib/python2.7/dist-packages/django/forms/forms.py" in __str__
  425.         return self.as_widget()
File "/usr/lib/python2.7/dist-packages/django/forms/forms.py" in as_widget
  475.         return widget.render(name, self.value(), attrs=attrs)
File "/usr/lib/python2.7/dist-packages/django/forms/widgets.py" in render
  504.         options = self.render_options(choices, [value])
File "/usr/lib/python2.7/dist-packages/django/forms/widgets.py" in render_options
  528.         for option_value, option_label in chain(self.choices, choices):

Exception Type: ValueError at /travel/senegal/
Exception Value: too many values to unpack

Answer 1

This has nothing to do with dynamic fields, nor about converting from a char field. The issue is solely that choices needs to be a 2- tuple - that is, a sequence of pairs.

choices = (('sample', Sample'), ('testing 'Testing'))
self.fields['duration']  = forms.ChoiceField(choices=choices, label="Duration")

Also note that your call to fields_for_model seems pointless: that has already been done by the superclass init method.