One RSVP per Email

Part of the Forms section of Coddy's Django journey. Lesson 18 of 20.

This chapter is yours: three features for the events board, built with what you know. Each task says what the site must do; the code is up to you.

Right now Ada can RSVP to Friday Jazz Night as often as she likes, and every RSVP takes a place. One email should hold one place per event.

You have every piece: a clean_<field> method, the event the form keeps in self.event, and its RSVPs in self.event.rsvps. One more lookup helps: email__iexact compares text without case, because Ada@Example.com and ada@example.com reach the same inbox.

Challenge

Medium

Refuse a second RSVP from the same email to the same event, with This email is already on the guest list. next to the email field.

Capitals do not matter: ADA@Example.com is ada@example.com.
The same email can still RSVP to another event.

RSVP to Friday Jazz Night as ADA@example.com: you see This email is already on the guest list.

Try it yourself

import datetime

from django import forms

from .models import RSVP, Event


class EventForm(forms.ModelForm):
    class Meta:
        model = Event
        fields = ["title", "date", "end_date", "place", "description", "capacity"]

    def clean_date(self):
        date = self.cleaned_data["date"]
        if date < datetime.date.today():
            raise forms.ValidationError("The date cannot be in the past.")
        return date

    def clean(self):
        cleaned_data = super().clean()
        date = cleaned_data.get("date")
        end_date = cleaned_data.get("end_date")
        if date and end_date and end_date < date:
            raise forms.ValidationError("The event cannot end before it starts.")
        return cleaned_data


class RSVPForm(forms.ModelForm):
    class Meta:
        model = RSVP
        fields = ["name", "email"]

    def __init__(self, *args, event=None, **kwargs):
        super().__init__(*args, **kwargs)
        self.event = event

    def clean(self):
        cleaned_data = super().clean()
        if self.event.rsvps.count() >= self.event.capacity:
            raise forms.ValidationError("Sorry, this event is full.")
        return cleaned_data