CharField values disappearing after save (readonly field)

Question

I'm implementing simple "grade book" application where the teacher would be able to update the grades w/o being allowed to change the students' names (at least not on the update grade page). To do this I'm using one of the read-only tricks, the simplest one. The problem is that after the SUBMIT the view is re-displayed with 'blank' values for the students. I'd like the students' names to re-appear.

Below is the simplest example that exhibits this problem. (This is poor DB design, I know, I've extracted just the relevant parts of the code to showcase the problem. In the real example, student is in its own table but the problem still exists there.)

models.py

class Grade1(models.Model):
    student = models.CharField(max_length=50, unique=True)
    finalGrade = models.CharField(max_length=3)

class Grade1OForm(ModelForm):
    student = forms.CharField(max_length=50, required=False)
    def __init__(self, *args, **kwargs):
        super(Grade1OForm,self).__init__(*args, **kwargs)
        instance = getattr(self, 'instance', None)
        if instance and instance.id:
            self.fields['student'].widget.attrs['readonly'] = True
            self.fields['student'].widget.attrs['disabled'] = 'disabled'
    def clean_student(self):
        instance = getattr(self,'instance',None)
        if instance:
            return instance.student
        else:
            return self.cleaned_data.get('student',None)
    class Meta:
        model=Grade1

views.py

from django.forms.models import modelformset_factory
def modifyAllGrades1(request):
    gradeFormSetFactory = modelformset_factory(Grade1, form=Grade1OForm, extra=0)
    studentQueryset = Grade1.objects.all()
    if request.method=='POST':
        myGradeFormSet = gradeFormSetFactory(request.POST, queryset=studentQueryset)
        if myGradeFormSet.is_valid():
            myGradeFormSet.save()
            info = "successfully modified"
    else:
        myGradeFormSet = gradeFormSetFactory(queryset=studentQueryset)
    return render_to_response('grades/modifyAllGrades.html',locals())

template

<p>{{ info }}</p>
<form method="POST" action="">
<table>
{{ myGradeFormSet.management_form }}
{% for myform in myGradeFormSet.forms %}
  {# myform.as_table #}
  <tr>
    {% for field in myform %}
    <td> {{ field }} {{ field.errors }} </td>
    {% endfor %}
  </tr>
{% endfor %}
</table>
<input type="submit" value="Submit">
</form>

Answer 1

I'm stretching myself a little here, so some thoughts:

% Have you sniffed the traffic to see exactly what's being sent between browser and server?

% Do you need to send the student name as a hidden field (your db update thing may assume you want student blank if you don't)?

% Have you looked at the source of your HTML after Python parses it?

Answer 2

Your way of displaying the readonly field is the problem.

Since the student field is disabled, the form submit will not have that as the input, so the error form that is displayed with validation error messages don't get the initial value.

That is why ReadOnly Widget has to be more complex than just being a html disabled field.

Try using a real ReadOnlyWidget, one that overrides _has_changed.

Following is what I use. For instantiation, it takes the original_value and optionally display_value, if it is different.

class ReadOnlyWidget(forms.Widget):

    def __init__(self, original_value, display_value=None):
        self.original_value = original_value
        if display_value:
            self.display_value = display_value
        super(ReadOnlyWidget, self).__init__()

    def _has_changed(self, initial, data):
        return False

    def render(self, name, value, attrs=None):
        if self.display_value is not None:
            return unicode(self.display_value)
        return unicode(self.original_value)

    def value_from_datadict(self, data, files, name):
        return self.original_value