Django join button to goal - django

Question

I try to create changing button after user join to Goal.
I have work buttons, but i don't know how to change this in template.
I try to do this with boolean field, when user click "Join", boolean field change to True, and then in template I try:
{% if goal.joined %}
<Delete join>
{% else %}
<join to goal>
{% endif %}
Models:
class Goal(models.Model, Activity):
title = models.CharField(max_length=255, verbose_name='Tytuł')
image = models.ImageField(upload_to='goals', verbose_name='Tło')
body = HTMLField(verbose_name='Treść')
tags = TaggableManager()
created_at = models.DateTimeField(auto_now_add=True)
author = models.ForeignKey(User, on_delete=models.CASCADE)
slug = AutoSlugField(populate_from='title')
def __str__(self):
return self.title
class Meta:
verbose_name = 'Cele'
ordering = ['-created_at']
def get_absolute_url(self):
return reverse('goaldetail', args=[str(self.slug)])
#property
def activity_actor_attr(self):
return self.author
def add_user_to_list_of_attendees(self, user):
registration = Joined.objects.create(user = user,
goal = self,
created_at = timezone.now())
def remove_user_from_list_of_attendees(self, user):
registration = Joined.objects.get(user = user, goal = self)
registration.delete()
class Joined(models.Model, Activity):
goal = models.ForeignKey(Goal, on_delete=models.CASCADE, related_name='joined')
user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='joined_users')
created_at = models.DateTimeField(auto_now_add=True)
joined = models.BooleanField(default=False)
def save(self, *args, **kwargs):
if self.id is None and self.created_at is None:
self.created_at = datetime.datetime.now()
self.joined = True
super(Joined, self).save(*args, **kwargs)
#property
def activity_actor_attr(self):
return self.user
Views:
def joined_add(request, pk):
this_goal = Goal.objects.get(pk=pk)
this_goal.add_user_to_list_of_attendees(user=request.user)
return redirect('goaldetail', slug=this_goal.slug)
def joined_delete(request, pk):
this_goal = Goal.objects.get(pk=pk)
this_goal.remove_user_from_list_of_attendees(request.user)
return redirect('goaldetail', slug=this_goal.slug)
def goaldetail(request, slug):
goal = get_object_or_404(Goal, slug=slug)
return render(request, 'goals/detail.html',
{'goal': goal})
Path:
path('joined/<int:pk>', views.joined_add, name='joined_add'),
path('joined-delete/<int:pk>', views.joined_delete, name='joined_delete'),
Create and delete works perfect, but on template this button don't change. I try in many ways and don't know how to do this.