Django foreign key is not set and hence unable to save form

Question

I have a simple foreign key relationship between two tables. I am able to save the parent, but am unable to save the child which has a foreign key to the parent. This is what my models look like:

class Product(models.Model):
    month_choices   = tuple((m,m) for m in calendar.month_abbr[1:])
    year_choices    = tuple((str(n), str(n)) for n in range(2004, datetime.now().year +2 ))
    id              = models.AutoField(primary_key = True)
    title           = models.CharField(max_length = 1024)
    product_type    = models.ForeignKey(ProductType)
    month           = models.CharField(max_length =3, choices=month_choices)
    year            = models.CharField(choices=year_choices, max_length = 4)
    project         = models.CharField(max_length = 15, null = True, blank = True)
    url             = models.URLField(null = True, blank = True)
    export_to_xsede = models.BooleanField()
    #def __str__(self):
    #    return str(self.id)
    class Meta:
        db_table = "product"

class ProductResource(models.Model):
    CHOICES             = (('A','A'),('B','B'),('C','C'),('D','D'),('E','E'))
    id                  = models.AutoField(primary_key = True)
    product             = models.ForeignKey(Product)
    resource            = models.CharField(choices=CHOICES, max_length = 15)

And my views:

class PublicationForm(forms.ModelForm):
        title = forms.CharField(widget=forms.TextInput(attrs={'size':'70'}),required=False)
        url = forms.CharField(widget=forms.TextInput(attrs={'size':'70'}),required=False)
        class Meta:
            model = Product
class ResourceForm(forms.ModelForm):
        resource = forms.MultipleChoiceField(choices=ProductResource.CHOICES, widget = forms.CheckboxSelectMultiple)
        class Meta:
            model = ProductResource

I save the parent:

saved_publication = publications_form.save()

but am unable to save the resource form:

resource_form = ResourceForm(request.POST, instance = saved_publication)
resource_form.product = saved_publication
resource_form.save()

When I print resource_form.errors, I get:

<ul class="errorlist"><li>product<ul class="errorlist"><li>This field is required.</li></ul></li></ul>

I have no idea why the foreign key is not getting set in this case.

Answer 1

I'm assuming you do not want to display the product field on the form, so you should exclude it from the form so the validation will pass:

class ResourceForm(forms.ModelForm):
    resource = forms.MultipleChoiceField(choices=ProductResource.CHOICES, widget = forms.CheckboxSelectMultiple)
    class Meta:
        model = ProductResource
        exclude = ['product']

Then in the view, just set the product manually after calling is_valid(). Just be sure to pass commit=False on the form.save() so that it will not actually save to the database until after you set the product. For example

...
saved_publication = publications_form.save()

resource_form = ResourceForm(request.POST)
if resource_form.is_valid():
    resource = resource_form.save(commit=False)
    resource.product = saved_publication
    resource.save()