ReverseManyToOne create object from children through django form - django

Question

Using:
Python 3.7.3
django 2.2.5
mysql 5.7.27
I have the following models:
class Item(models.Model):
...
class Comments(models.Model):
Item = models.ForeignKey('Item', default=None, null=True, on_delete=models.CASCADE)
Comment = models.TextField(max_length=512, default="", blank=True)
I would like to create a Comments object, when creating the Item through a django form. I tried to do:
class ItemInsertForm(forms.ModelForm):
...
Comments = forms.CharField(required=False,
widget=forms.Textarea(attrs={'placeholder':"Use comments to describe item details \
or issues that other users should know",
'rows':5,
'cols':50,
}
)
)
def clean_Comments(self, *args, **kwargs):
_comment = self.cleaned_data.get('Comments')
_comments = Item.comments_set.create(Comment=_comment)
return _comments
but I get the following error:
'ReverseManyToOneDescriptor' object has no attribute 'create'
Both tables are empty, so no Item and no Comments currently exist. I guess that's why there is no 'create' method available. Is there a way I could achieve what I want?
Or is there another way to manage the comments for the Item object? I created another table to be able to associate multiple comments to the same item and differentiate between them. A character field in the Item class would concatenate all comments in a single string.

Answer 1

I see quite some issues with your code, but since I feel like you gave it an honest shot, I'll try to help you out as best as I can.
First of all your models.py file:
Model names should be singular, so instead of Comments, use Comment.
Class members should be lowercase, so Item and Comment should be changed to item and comment.
Comment.comment is still not very descriptive. The comment is the actual object, it's content is the text within the comment, so text would be more appropriate here.
A ForeignKey with null=True already sets default to None.
Taking this into account and cleaning up your models.py:
class Item(models.Model):
...
class Comment(models.Model):
item = models.ForeignKey(Item, null=True, on_delete=models.CASCADE)
text = models.TextField(max_length=512, default="", blank=True)
Then, moving on to your form:
Since it's a form for creation Comments, a more appropriate name would be CommentForm.
def clean_Comments(self, *args, **kwargs): is a function reserved for doing validation on the Comments field, not for creating an object from the form input. For that you can use the ModelForm's save() method. You only need to define a save method if you're going to perform some custom logic though.
Let's fix those issues first, before I move onto the error message your getting:
class ItemInsertForm(forms.ModelForm):
class Meta:
model = Comment
fields = ['text']
text = forms.CharField(required=False,
widget=forms.Textarea(attrs={'placeholder':"Write your comment to describe item details \
or issues that other users should know",
'rows':5,
'cols':50,
}
)
)
This form, when submitted, will create a Comment object. However, there is still no ability to add the comment to an Item.
To do this, you need to make sure there are Item instances in the database, or allow the user to create one through an ItemForm
There are multiple ways to do this:
Add a ModelChoiceField to the CommentForm, which will allow the user to select an item from a select.
item = forms.ModelChoiceField(queryset=Item.object.all(),
to_field_name = '<item_name>',
empty_label="Select an Item")
When you want to add this form to an something like an ItemDetailPage, you can use the currently viewed Item using something like
item = Item.objects.get(pk=<item_id>)
or
item = Item.objects.create(<item_properties_here>)
then, when saving your form:
comment = form.save()
comment.item = item.
comment.save()
The third way is what you were trying, and why you were getting an error. Retrieve an item, then add the comment saved from the form to the item.comment_set.
Something like this:
item = Item.objects.get(pk=<item_id>)
comment = form.save()
item.comments_set.add(comment)
item.save()