Django selected value using manual render form in django - django

Question

I'm trying to implement CRUD operations in django, however, I'm stuck in the edit operation.
After passing the data to edit template I need to show the selected values of operating system dropdown list, how can I achieve that?
I utilized the manual rendering of django form with the following code in the template:
<div class="form-group row">
<label class="col-sm-3 col-form-label">Operating System</label>
<div class="col-sm-9">
<select class="form-control" name="os_id" id="os_id" required>
<option value="">--Select--</option>
{% for os in os %}
<option value="{{ os.id}}">{{ os.key_name}}</option>
{% endfor %}
</select>
</div>
</div>
<div class="form-group row">
<label class="col-sm-3 col-form-label">Title</label>
<div class="col-sm-9">
<textarea class="form-control" id="title" name="title" rows="3" required>{{ servicedesk.title }}</textarea>
</div>
</div>
here's the view code:
def edit(request, id):
servicedesk=Servicedesk.objects.get(id=id)
softwares=Software.objects.all
os=OperatingSystem.objects.all
context = {'servicedesk':servicedesk, "softwares":softwares, "os":os}
return render(request, 'servicedesks/edit.html', context)
and the model:
class OperatingSystem(models.Model):
key_name = models.CharField(max_length=100,null=True)
key_description = models.CharField(max_length=255,null=True)
class Meta:
db_table = "operating_systems"
def __str__(self):
return self.key_name
class Software(models.Model):
key_name = models.CharField(max_length=100,null=True)
key_description = models.CharField(max_length=255,null=True)
class Meta:
db_table = "softwares"
def __str__(self):
return self.key_name
class Servicedesk(models.Model):
os_id=models.ForeignKey(OperatingSystem, on_delete=models.SET(0))
software_id = models.ForeignKey(Software, on_delete=models.SET(0))
title = models.CharField(max_length=255,null=True)
I tried this but it's not working:
<div class="form-group row">
<label class="col-sm-3 col-form-label">Operating System {{os_id}}</label>
<div class="col-sm-9">
<select class="form-control" name="os_id" id="os_id" required>
<option value="">--Select--</option>
{% for os in os %}
{% if os.id == servicedesk.os_id %}
<option value="{{os.id}}" selected>{{os.key_name}}</option>
{% endif %}
<option value="{{ os.id}}">{{ os.key_name}}</option>
{% endfor %}
</select>
</div>
</div>