MultichoiceField in ModelForm for Django with DB relations

from django import forms
from .models import Project
class ProjectForm(forms.ModelForm):
    def __init__(self, *args, **kwargs):
        assigned_users = kwargs.pop('assigned_to', [])
        super(ProjectForm, self).__init__(*args, **kwargs)
        for field in self.fields.values():
            field.widget.attrs = {"class": "form-control"}
        self.fields['project_name'].required = True
        self.fields['project_url'].required = True

        if assigned_users:
            self.fields['assigned_to'].queryset = assigned_users
        self.fields['assigned_to'].required = True

        self.fields['project_name'].widget.attrs.update({
            'placeholder': 'Project Name'})
        self.fields['project_url'].widget.attrs.update({
            'placeholder': 'Project URL'})
    class Meta:
        model = Project
        fields = ('project_name', 'project_url', 'assigned_to')

def create_project(request):
    template_name = "create.html"
    users = []

    form = ProjectForm(assigned_to=users)

    if request.method == 'POST':
        form = ProjectForm(request.POST, request.FILES, assigned_to=users)
        if form.is_valid():
            proj_obj = form.save(commit=False)
            proj_obj.created_by = request.user
            proj_obj.save()

            if request.POST.getlist('assigned_to', []):
                proj_obj.assigned_to.add(*request.POST.getlist('assigned_to'))
                assigned_to_list = request.POST.getlist('assigned_to')
            success_url = reverse('projects:list')
            if request.POST.get("savenewform"):
                success_url = reverse("leads:add_lead")
            return JsonResponse({'error': False, 'success_url': success_url})
        return JsonResponse({'error': True, 'errors': form.errors})
    context = {}
    context["proj_form"] = form
    context["users"] = users

    context["assignedto_list"] = [
        int(i) for i in request.POST.getlist('assigned_to', []) if i]

    return render(request, template_name, context)

<div class="form-control">
    {{ proj_form.project_name }}
    {{ proj_form.assigned_to }}
    {{ proj_form.project_url }}

</div>