[Answered ]-Django modelform validation get field from db if not if form

Change your form for it:

class SettingsForm(forms.ModelForm):
    class Meta:
        model = Settings

    def __init__(self, *args, **kwargs):
        super(SettingsForm, self).__init__(*args, **kwargs)

    def clean(self):
        cleaned_data = super(SettingsForm, self).clean()
        field_1 = cleaned_data.get('field_1','')
        if not field_1:   # field_2 is disabled 
            cleaned_data['field_2'] = self.instance.field_2 # so get from db
        self.cleaned_data = cleaned_data
        return self.cleaned_data