In Django, how to check if user is in site_id (site_id are created by after)

the objective of the system is to check if the user is in such site_id or not to display a part of the html page to him

here I do it with groups :

views.py

def is_admin(user):
    return user.groups.filter(id=1).exists()

def is_client(user):
    return user.groups.filter(id=4).exists()

template (main_list.html)

{% for group in request.user.groups.all %}
    {% if 1 == group.id %}

and I would like to do it with my site_id (Foreign Key)

here is my first attempt :

views.py

def is_siteone(user):
    return user.site_id.filter(id=1).exists()

template (main_list.html)

{% if is_siteone %}

models.py

class Site(models.Model):
    name = models.CharField(max_length=100)
    address = models.CharField(max_length=255)
    version = models.CharField(verbose_name='Program version', blank=False, default='1.0', max_length=20)

    def __str__(self):
        return self.name

    def filter(self, id):
        pass

but it returns the following error
error return

Do you have any ideas on how to proceed?

My site_id is a Foreign key of a Site table in table auth_user of Django

Here is what I was able to do:

views.py

def is_siteone(user):
    return user.site_id == 1 if user.site_id else False

template (main_list.html)

<h1>{{ user.site_id }}</h1>
    <p>---</p>
    <h1>{{ is_siteone }}</h1>

{#    {% for user in request.user.site.id %}#}
    {% if is_siteone %}

my balise {{ user.site_id }} return siteone in text and my balise {{ is_siteone }} return False

so I modified my code in views.py like this:

def is_siteone(user):
    return user.site_id == "siteone" if user.site_id else False

I specify that my context is like this, so I don't add (request.user) in the template

"is_siteone": is_siteone(request.user),

It seems like you are trying to access the site_id attribute directly from the user object, but site_id is not a direct attribute of the User model. Instead, it is a foreign key that relates the User model with the Site model, so try to do something like:

def is_siteone(user):
    return user.site_id == 1 if user.site_id else False

Then in the template, use the function like this:

{% if is_siteone(request.user) %}
    <!-- some content -->
{% endif %}