i am learning Django right now and still struggling with it. I have two models: Database and DatabaseUser, linked with a foreign-key. In the admin page, I want to add a link to the list with databases, that directs me to a list with database-users of that specific database.

Python: 3.9; Django: 4.2.13

# models.py


class Database(models.Model):
    datenbank_name = models.CharField(max_length=300)
    datenbank_art = models.CharField(max_length=100)
    # ... (omitted some attributes)

    def __str__(self):
        return self.datenbank_name

class DatabaseUser(models.Model):
    datenbank = models.ForeignKey(Database, on_delete=models.CASCADE)
    user_name = models.CharField(max_length=300)
    # ... (omitted some attributes)

    def __str__(self):
        return self.user_name

My admin models are looking like this:

# admin.py

class PasswordInput(forms.ModelForm):
    passwort = forms.CharField(widget=forms.PasswordInput())


class DatabaseAdmin(admin.ModelAdmin):
    form = PasswordInput
    fieldsets = [
        ("Allgemein", {"fields": ["datenbank_name", "datenbank_art", "kunde", "host", "port"]}),
        ("Anmeldeinformationen", {"fields": ["user_name", "passwort"]}),
    ]
    
    list_display = ["datenbank_name", "kunde", "datenbank_art", "port", "erreichbar"]

admin.site.register(Database, DatabaseAdmin)



class DatabaseUserAdmin(admin.ModelAdmin):
    form = PasswordInput
    fieldsets = [
        ("Datenbank", {"fields": ["datenbank"]}),
        ("Anmeldeinformationen", {"fields": ["user_name", "passwort"]}),
        ("Datenbank-Rechte", {"fields": ["rechte"]}),
    ]
    list_filter = ["datenbank"]

    list_display = ["user_name", "rechte", "datenbank"]

admin.site.register(DatabaseUser, DatabaseUserAdmin)

Now I have tried couple of things and found 2 very similar questions on Stack Overflow. However i couldn’t get them to work in my code. The second one is not creating a link to the list of objects, but to the change-view (as far as I’ve understood).

• How can I list all foreign key related objects in Django admin panel?
• Link in django admin to foreign key object

From the first thread (How can I list all foreign key related objects in Django admin panel?) I have tried all three solutions. Unfortunately without success:

My attempt for first solution:

def users(self):
    return '<a href="/admin/db_manager/databaseuser/?datenbank__id__exact=%d">%s</a>' % (
    self.datenbank_id, self.datenbank)

users.allow_tags = True

list_display = ["datenbank_name", "users", "kunde", "datenbank_art", "port", "erreichbar"]

Errors:

• In my code self.datenbank_id and self.datenbank are beeing highlighted by PyCharm, saying “Unresolved attribute reference ‘datenbank_id’ for class ‘DatabaseAdmin'”

• Furthermore when I try to open the admin site, it says “users() takes 1 positional argument but 2 were given”

If I add obj to the function: def users(self, obj): The error is either “‘DatabaseAdmin’ object has no attribute ‘datenbank_id'” (if self.datenbank_id is used) or ‘Database’ object has no attribute ‘datenbank_id’ (if obj.datenbank_id is used)

Just can’t figure it out.

My attempt for the second solution:

# models.py 
def get_admin_url(self):
    return "/admin/db_manager/databaseuser/%d/" % self.id

# admin.py 
def databases(self, obj):
    html = ""
    for obj in DatabaseUser.objects.filter(datenbank__id_exact=self.id):
        html += '<p><a href="%s">%s</a></p>' % (obj.get_admin_url(), obj.title)
    return html

databases.allow_tags = True

list_display = ["user_name", "rechte", "datenbank", "databases"]

Errors:

• PyCharm highlights self.id objects in DatabaseUser.objects.filter and self.id in the get_admin_url() function.
• Similar other errors than with the first solution. E.g.: adding obj to function parameters

I have then tried a solution of the second link (Link in django admin to foreign key object) and: Surprise. I got something that at least loads:

def users(self, obj:DatabaseUser):
    link = reverse("admin:db_manager_databaseuser_change", args=[obj.pk])
    return mark_safe(f'<a href="{link}">{escape(obj.__str__())}</a>')

users.allow_tags = True

list_display = ["datenbank_name", "users", "kunde", "datenbank_art", "port", "erreichbar"]

Problem is, that the second thread about a slightly different problem. In the list view of the database a link is shown, as I wanted it, in an own column, next to each database.
However this link directs me to the change form, where I can make changes to the attributes of a specific user. Not the list as I wanted it.

I tried to change link = reverse("admin:db_manager_databaseuser_change", args=[obj.pk]) to link = reverse("admin:db_manager_databaseuser_changelist", args=[obj.pk]). But this will throw me an error:
Reverse for 'db_manager_databaseuser_changelist' with arguments '(2,)' not found. 1 pattern(s) tried: ['admin/db_manager/databaseuser/\Z']

I think one of the main problems for me here is, that I have started with Django like 1 Week ago and until now I can’t get my head around, how everything is connected.
I am a bit desperate right now. I would really appreciate any help, to get this fixed.

Greetings.