Django: Reverse lookup of optional foreignkey-entry and inclusion in dataset

I would like to compose list of database entries, and corresponding (but not necessarily existing) related entries in another table.

The concrete context is a list of events, in which the user should be able to see, whether he already stated his participation (thus has an entry in the database which should be displayed) or not (which would give him a link to a participation form)

My models (minimal):

class Event(models.Model):
    title = models.CharField(max_length = 200)
    #...

class Event_Participation(models.Model):
    EVENT_PARTICIPATION_CHOICES = [
        ("Y", "Yes"),
        ("N", "No"),
         # few other options
    ]
    event = models.ForeignKey(Event, on_delete=models.CASCADE)
    participation = models.CharField(max_length=1, choices= EVENT_PARTICIPATION_CHOICES)
    user = models.CharField(max_length=10) #originally another foreign key

Ideally, I'm searching for one expression like Event.appendIfExists(Event_Participation)...

For template rendering, I was able to query the data, but this doesn't seem elegant and I don't know, how to merge the information inside the template:

def event_list(request):
    e_all = Event.objects.all() #normally filtered
    part_list = {}
    for e in e_all:
        if e.event_participation_set.get(user_id = request.user.id) :
            p = e.event_participation_set.get(user_id = request.user.id).participation
        else:
            p = "X"
        part_list[e.id]= p
        context = {"part_list":part_list,"full_event_list":e_all}
        return render(request, "event_list.html", context)

An index-based variable in the template did not work for part_list, and I was not able to extend the queries in a way, which allowed me to use only one dict like this:

{% for event in full_event_list %}
        <li> {{ event.title }}
           {# Participation: {% if event.participation %} {{ event.participation }} {% else %} LINK {%endif%}
        </li>
    {% endfor %}

Since this seems like a very common application, I am probably missing something very obvious...

We could use select_related or prefetch_related methods to perform database joins and reduce the number of queries.

We want Event objects along with their related Event_Participation objects for the current user.

from django.db.models import Prefetch

def event_list(request):
    participations = Event_Participation.objects.filter(user_id=request.user.id)
    events = Event.objects.all().prefetch_related(
        Prefetch('event_participation_set', queryset=participations, to_attr='user_participations')
    )

    return render(request, "event_list.html", {'events': events})

then in our template we can access the related Event_Participation objects for each event

{% for event in events %}
    <li>
        {{ event.title }}
        {% for participation in event.user_participations %}
            Participation: {{ participation.participation }}
        {% empty %}
            LINK
        {% endfor %}
    </li>
{% endfor %}