Odd behavior in Django Form (read-only / widget)

Question

I am having a problem with a test application that I am writing to test the functionality of Django. The test application is a small classroom application that currently uses Alex Gaynor flight functionality to read only http://lazypython.blogspot.com/2008/12/building-read-only-field-in- django.html

There are two problems that may be related. First, when I overlay a comment on these two lines below:

# myform = GradeForm(data=request.POST, instance=mygrade) myform = GradeROForm(data=request.POST, instance=mygrade) 

it works as I expect, except that the student field is volatile.

When comments are displayed in this order, the "studentId" field is displayed as a number (not a name, problem 1), and when I click submit, I get an error saying that studentId must be an instance of Student.

I don’t understand how to fix this. I am not tied to Alex Gaynor code. Any code will work. I'm relatively new to both Python and Django, so the tips I saw on websites that say “make the read-only field easy” still don't fit me.

//models.py

 class Student(models.Model): name = models.CharField(max_length=50) parent = models.CharField(max_length=50) def __unicode__(self): return self.name class Grade(models.Model): studentId = models.ForeignKey(Student) finalGrade = models.CharField(max_length=3) # testbed.grades.readonly is alex gaynor code from testbed.grades.readonly import ReadOnlyField class GradeROForm(ModelForm): studentId = ReadOnlyField() class Meta: model=Grade class GradeForm(ModelForm): class Meta: model=Grade 

//views.py

 def modifyGrade(request,student): student = Student.objects.get(name=student) mygrade = Grade.objects.get(studentId=student) if request.method == "POST": # myform = GradeForm(data=request.POST, instance=mygrade) myform = GradeROForm(data=request.POST, instance=mygrade) if myform.is_valid(): grade = myform.save() info = "successfully updated %s" % grade.studentId else: # myform=GradeForm(instance=mygrade) myform=GradeROForm(instance=mygrade) return render_to_response('grades/modifyGrade.html',locals()) 

//template

 <p>{{ info }}</p> <form method="POST" action=""> <table> {{ myform.as_table }} </table> <input type="submit" value="Submit"> </form> 

// Code Alex Gaynor

 from django import forms from django.utils.html import escape from django.utils.safestring import mark_safe from django.forms.util import flatatt class ReadOnlyWidget(forms.Widget): def render(self, name, value, attrs): final_attrs = self.build_attrs(attrs, name=name) if hasattr(self, 'initial'): value = self.initial return mark_safe("<span %s>%s</span>" % (flatatt(final_attrs), escape(value) or '')) def _has_changed(self, initial, data): return False class ReadOnlyField(forms.FileField): widget = ReadOnlyWidget def __init__(self, widget=None, label=None, initial=None, help_text=None): forms.Field.__init__(self, label=label, initial=initial, help_text=help_text, widget=widget) def clean(self, value, initial): self.widget.initial = initial return initial 

Answer 1

Do not worry about ReadOnlyField. Use the widget instead.

Here is the one I use regularly.

 class ReadOnlyWidget(forms.Widget): def __init__(self, original_value, display_value): self.original_value = original_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 

Use it with CharField.

Answer 2

Django 1.2 (released about a year and a half ago) only supports reading fields for the administrator:

http://docs.djangoproject.com/en/dev/ref/contrib/admin/#django.contrib.admin.ModelAdmin.readonly_fields

I'm not sure how difficult it is to extend this new functionality to something like ModelForm that will appear on your site, but it will be a more relevant starting point than Alex (excellent, but dated) code.