django：如何限制formset中的字段选择？

我在限制formset中的可选选项时遇到了问题.我有以下模型：员工,部门,项目,项目类型,成员资格和角色.员工可以在表单集中添加/删除他们为给定部门项目播放的角色,表单应该将可选项目限制为仅属于员工所属部门的项目.

楷模：

class Department(models.Model):
    name = models.CharField(max_length=20)
    def __unicode__(self):
    return self.name

class Employee(models.Model):
    fname = models.CharField(max_length=15)
    department = models.ForeignKey(Department)
    def __unicode__(self):
        return self.fname

class Projecttype(models.Model):
    name = models.CharField(max_length=20)
    def __unicode__(self):
        return self.name

class Project(models.Model):
    projecttype = models.ForeignKey(Projecttype)
    department = models.ForeignKey(Department)
    members = models.ManyToManyField(Employee,through='Membership')
    def __unicode__(self):
       return "%s > %s" % (self.department,self.projecttype)

class Role(models.Model):
    name = models.CharField(max_length=20)
    def __unicode__(self):
       return self.name

class Membership(models.Model):
    project = models.ForeignKey(Project,null=True)
    department = models.ForeignKey(Department)
    employee = models.ForeignKey(Employee)
    role = models.ManyToManyField(Role,blank=True,null=True)
    class Meta:
        unique_together = (("project","employee",),)

视图：

def employee_edit(request,employee_id):
    i = get_object_or_404(Employee,pk=employee_id)
    MembershipFormSet = modelformset_factory(Membership,exclude=('department','employee'),)
    f = MembershipFormSet(queryset=Membership.objects.filter(employee=i),)
    return render_to_response('gcs/edit.html',{'item': i,'formset': f,},context_instance=RequestContext(request))

现在,欧盟可以为任何部门项目选择一个角色.它的行为如下：

项目选择：

Projects.objects.all()

我想用这样的方式限制项目：LIMIT PROJECT CHOCIES TO：

Projects.objects.filter(department=i.department)

from django.http import HttpResponseRedirect

def make_membership_form(employee):
    """
    Returns a Membership form for the given employee,restricting the Project choices to those in the 
    employee's department. 
    """
    class MembershipForm(forms.ModelForm):
        project = forms.ModelChoiceField(queryset=Projects.objects.filter(department=employee.department))
        class Meta:
            model = Membership
            excludes = ('department','employee',)
    return MembershipForm

def employee_edit(request,employee_id):
    employee = get_object_or_404(Employee,pk=employee_id)
    # generate a membership form for the given employee
    MembershipForm = make_membership_form(employee)
    MembershipFormSet = modelformset_factory(Membership,form=MembershipForm)

    if request.method == "POST":
        formset = MembershipFormSet(request.POST,queryset=Membership.objects.filter(employee=employee))
        if formset.is_valid():
            instances = formset.save(commit=False)
                for member in instances:
                    member.employee = employee
                    member.department = employee.department
                    member.save()
            formset.save_m2m()
            # redirect after successful update
            return HttpResponseRedirect("")
    else:
        formset = MembershipFormSet(queryset=Membership.objects.filter(employee=employee),)
    return render_to_response('testdb/edit.html',{'item': employee,'formset': formset,context_instance=RequestContext(request))