django: ForeignKeyField limit_choices_to "parents pk"? - django

Question

I've a model (Parent model):
class Post(models.Model):
image = models.ImageField(upload_to='%Y/%m/%d')
title = models.CharField(max_length=200)
width = models.DecimalField(max_digits=3, decimal_places=0)
height = models.DecimalField(max_digits=3, decimal_places=0)
year = models.PositiveIntegerField()
def __str__(self):
return self.title
and another model (Child model):
class Addimg(models.Model):
post = models.ForeignKey('Post', null=True)
addimg = models.ImageField(upload_to='%Y/%m/%d')
def __str__(self):
return self.post
My Addimg Form:
class AddimgForm(forms.ModelForm):
class Meta:
model = Addimg
fields = ('post', 'addimg', 'width', 'height',)
views.py using the form:
def addimg(request, pk):
if request.method == "POST":
form = AddimgForm(request.POST, request.FILES)
post = get_object_or_404(Post, pk=pk)
if form.is_valid():
addimg = form.save(commit=False)
addimg.addimg = request.FILES['addimg']
addimg.save()
return redirect('blog.views.detail', pk=post.pk)
else:
form = AddimgForm()
return render(request, 'blog/edit.html', {'form': form})
And my Problem is that when I create a "Child model" my post field returns all instances of allready created Post models as choices. What I want is that it automatic only displays the one Post it is related to without choices. Is ForeignKey the right model for that?
Any Ideas how this could work. thanks

Answer 1

ForeignKey field is translated into ModelChoiceField inside a Django ModelForm. If you inspect that class you will notice that this type of field has an queryset attribute required. By default Django provides the full set of objects. You can override this inside your form __init__ method by providing the parent object the form will need.
Consider the following example code:
def addimg(request, pk):
post = get_object_or_404(Post, pk=pk)
if request.method == "POST":
form = AddimgForm(request.POST, request.FILES, post=post)
#...
else:
form = AddimgForm(post=post)
return render(request, 'blog/edit.html', {'form': form})
class AddimgForm(forms.ModelForm):
class Meta:
model = Addimg
fields = ('post', 'addimg', 'width', 'height',)
def __init__(self, *args, **kwargs):
post = kwargs.pop('post')
super(AddimgForm, self ).__init__(*args, **kwargs)
self.fields['post'].queryset = Post.objects.filter(id=post.id)

Answer 2

What you want to do is create a Many-to-one relationship. For example,
post = models.ForeignKey('Post', null=True)
This means you can filter on it for example,
Addimg.objects.filter(post=Post)
or
Post.objects.get(pk=1)
Post.addimg_set.filter(xyz=etc)
Read more here: https://docs.djangoproject.com/en/1.8/topics/db/examples/many_to_one/