How do I add a Foreign Key Field to a ModelForm in Django?

Question

What I would like to do is to display a single form that lets the user:

• Enter a document title (from Document model)
• Select one of their user_defined_code choices from a drop down list (populated by the UserDefinedCode model)
• Type in a unique_code (stored in the Code model)

I'm not sure how to go about displaying the fields for the foreign key relationships in a form. I know in a view you can use document.code_set (for example) to access the related objects for the current document object, but I'm not sure how to apply this to a ModelForm.

My model:

class UserDefinedCode(models.Model):     name = models.CharField(max_length=8)     owner = models.ForeignKey(User)  class Code(models.Model):     user_defined_code = models.ForeignKey(UserDefinedCode)     unique_code = models.CharField(max_length=15)  class Document(models.Model):     title = models.CharField(blank=True, null=True, max_length=200)     code = models.ForeignKey(Code)     active = models.BooleanField(default=True) 

My ModelForm

class DocumentForm(ModelForm):     class Meta:         model = Document 

Answer 1

In regards to displaying a foreign key field in a form you can use the forms.ModelChoiceField and pass it a queryset.

so, forms.py:

class DocumentForm(forms.ModelForm):     class Meta:         model = Document      def __init__(self, *args, **kwargs):         user = kwargs.pop('user','')         super(DocumentForm, self).__init__(*args, **kwargs)         self.fields['user_defined_code']=forms.ModelChoiceField(queryset=UserDefinedCode.objects.filter(owner=user)) 

views.py:

def someview(request):     if request.method=='post':         form=DocumentForm(request.POST, user=request.user)         if form.is_valid():             selected_user_defined_code = form.cleaned_data.get('user_defined_code')             #do stuff here     else:         form=DocumentForm(user=request.user)      context = { 'form':form, }      return render_to_response('sometemplate.html', context,          context_instance=RequestContext(request)) 

from your question:

I know in a view you can use document.code_set (for example) to access the related objects for the current document object, but I'm not sure how to apply this to a ModelForm.

Actually, your Document objects wouldn't have a .code_set since the FK relationship is defined in your documents model. It is defining a many to one relationship to Code, which means there can be many Document objects per Code object, not the other way around. Your Code objects would have a .document_set. What you can do from the document object is access which Code it is related to using document.code.

edit: I think this will do what you are looking for. (untested)

forms.py:

class DocumentForm(forms.ModelForm):     class Meta:         model = Document         exclude = ('code',)      def __init__(self, *args, **kwargs):         user = kwargs.pop('user','')         super(DocumentForm, self).__init__(*args, **kwargs)         self.fields['user_defined_code']=forms.ModelChoiceField(queryset=UserDefinedCode.objects.filter(owner=user))         self.fields['unique_code']=forms.CharField(max_length=15) 

views.py:

def someview(request):     if request.method=='post':         form=DocumentForm(request.POST, user=request.user)         if form.is_valid():             uniquecode = form.cleaned_data.get('unique_code')             user_defined_code = form.cleaned_data.get('user_defined_code')             doc_code = Code(user_defined_code=user_defined_code, code=uniquecode)             doc_code.save()             doc = form.save(commit=False)             doc.code = doc_code             doc.save()             return HttpResponse('success')     else:         form=DocumentForm(user=request.user)      context = { 'form':form, }      return render_to_response('sometemplate.html', context,          context_instance=RequestContext(request)) 

actually you probably want to use get_or_create when creating your Code object instead of this.

doc_code = Code(user_defined_code=user_defined_code, code=uniquecode)