django admin - select reverse foreign key relationships (not create, I want to add available)

Question

Lets say I have a model School and another model Student.

class Student(models.Model):
   school = models.ForeignKey(School)
   name = models.CharField(max_length=100)

When a school is clicked in admin, then a new page appears showing school model fields and values.

I also want to select the already available list of students in that page itself.

Inlines is different, they will allow the ability to create and edit new records(student) belonging to that school. But I don't want that, lets assume there are already many student records available. I should be able to select them in admin from that school model page.

Answer 1

class SchoolAdminForm(forms.ModelForm):
    students = forms.ModelMultipleChoiceField(
        queryset=Student.objects.all(),
        widget=FilteredSelectMultiple(verbose_name='students', is_stacked=False))

    class Meta:
        model = School
        fields = ['your_school_fields_go_here']

    def __init__(self, *args, **kwargs):
        super(SchoolAdminForm, self).__init__(*args, **kwargs)
        if self.instance:
            # fill initial related values
            self.fields['students'].initial = self.instance.student_set.all()

class SchoolAdmin(admin.ModelAdmin):
   form = SchoolAdminForm

   def save_model(self, request, obj, form, change):
       super().save_model(request, obj, form, change)
       original_students = set(obj.student_set.values_list("id", flat=True))
       current_students = set(map(lambda x: x.id, form.cleaned_data['students']))
       if original_students != current_students:
           add_to_school = current_students - original_students
           Student.objects.filter(id__in=add_to_school).update(school_id=obj.id)
           remove_from_school = original_students - current_students
           Student.objects.filter(id__in=remove_from_school).update(school_id=None)