views.py

<...>
    def form_valid(self, form):
        form.instance.ip = self.request.META["REMOTE_ADDR"]
        form.nickname = self.request.user.username
        form.instance.approved = False
        form.save()  # add post to the database
        return super(PostSubmissionView, self).form_valid(form)
<...>

models.py
<...>
nickname = models.CharField(_("Nickname*"), max_length=20, db_index=True,
                                validators=[RegexValidator(r'^[A-z0-9-_]+$',
                                                           _("Nickname must consist of letters and numbers only."))])

<...>