modifying django model forms after post - django

Question

I would like to modify a user submitted form to automatically insert the project_id, but I keep getting the error that project_id in the Employee model cannot be null;
My model:
class Project(models.Model):
name = models.CharField(max_length=100)
date_started = models.DateTimeField()
class Employee(models.Model):
name = models.CharField(max_length=200)
project = models.ForeignKey(Project)
class AddEmployeeForm(ModelForm):
class Meta:
model = Employee
exclude = ('project',)
My view:
def emp_add(request, project_id):
if request.method == 'POST':
post = request.POST.copy() # make the POST QueryDict mutable
post('project', project_id)
form = AddEmployeeForm(post)
if form.is_valid():
saved = form.save()

Answer 1

Like this?
if form.is_valid():
employee = form.save(commit=False)
employee.project = Project.objects.get(pk=project_id)
employee.save()

Answer 2

#maciag.artur's answer, to save with commit=False will work. Another way is to instantiate an Employee with the required project_id, and use it to construct the form.
This is useful if your model form's custom clean method relies on the Employee.project field.
def emp_add(request, project_id)
if request.method == 'POST':
# create a new employee with the given project id
employee = Employee(project_id) = project_id
form = AddEmployeeForm(request.POST, instance=employee)
if form.is_valid():
saved = form.save()
<snip>
For reference, see the note box below Using a subset of fields on the form in the Django docs.

Answer 3

Add the project ID to the form as a hidden input. When the request comes back as a POST, it will exist in the POST object, from the form.
def emp_add(request, project_id):
if request.method == 'POST':
post = request.POST.copy() # make the POST QueryDict mutable
post('project', project_id)
form = AddEmployeeForm(post)
if form.is_valid():
saved = form.save()
else:
form = AddEmployeeForm(initial={'project_id':'my_id_value'})