[Answer]-Django – how can I make a cell in a table in the admin *changelist* interface editable only if it is null?

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If your field uses an input element, such as a TextField, add the readonly attribute to the field’s widget’s attrs dict in the changelist form’s __init__ method. Something like this:

class PamphletChangeListForm(forms.ModelForm):

    def __init__(self, *args, **kwargs):
        super(PamphletChangeListForm, self).__init__(*args, **kwargs)
        instance = kwargs.get('instance')
        if instance:
            self.fields['book'].queryset = Book.objects.filter(
                size=instance.size
            )
            if instance.size is not None:
                self.fields['size'].widget.attrs['readonly'] = 'readonly'

That won’t protect you against a malicious user faking post data – for that you’d need to customize your admin further. But if you have malicious users on your admin you have bigger problems.

If your field uses a select element, you have to change it more – select attributes don’t have readonly as a supported attribute. Instead, you’ll want a hidden input with the unchanging value, and a text representation so the user can see what the setting is. Django does not include such a widget, but you can define your own:

class LabeledHiddenInput(forms.widgets.HiddenInput):
    def render(self, name, value, attrs=None):
        base_output = super(LabeledHiddenInput, self).render(name, value, attrs)
        if value:
            return base_output + unicode(value)
        else:
            return base_output

You might need more careful escaping or even some HTML formatting, this is just a quick example. Check the source code for the built in widgets if you need more examples.

Then you can use that widget instead of the default select:

        if instance.size is not None:
            self.fields['size'].widget = LabeledHiddenInput()
👤Peter DeGlopper

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