initialize modelformset with manytomanyfield
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03-12-2019 - |
Question
All,
I am trying to initialize a modelformset with a manytomanyfield. A catch is that I do not know in advance the name of the manytomanyfield (nor the class it is bound to).
Here are my models and forms:
class Book_model(models.Model):
title = models.CharField(max_length=BIG_STRING)
authors = models.ManyToManyField("Author_model",)
class Author_model(models.Model):
name = models.CharField(max_length=BIG_STRING)
class Book_form(ModelForm):
class Meta:
model = Book_model
class Author_form(ModelForm:
class Meta:
model = Author_model
Author_formset = modelformset_factory(Author_model,form=Author_form)
And elsewhere in my code I am trying to display a Model_form along with an Author_formset. When it comes time to initialize that formset, though, I'm not sure what to do. At that point I know the name of the m2m field ("authors"), the parent model instance (Book_model), the parent form instance (Book_form), and the formset class (Author_formset). I assume that I just need to do something like this:
m2m_field = getattr(book,"authors")
qset = field.filter(<only authors for which there is a m2m relationship from this book>)
formset = Author_formset(queryset=qset)
But, I don't know the right terms to put in the filter.
Any suggestions?
Solution 2
I think I have solved this.
In theory this is the correct way to do things, as Daniel suggests:
formset = Author_formset(queryset=book.authors.all())
But I can't do that directly, because I am trapped in some generic code that could be called for any model/form/formset. So I'm forced to do this instead:
# these 4 lines are just for clarity's sake
# I don't actually know what these map to in my code
MyModelClass = Book_model
MyFormClass = Book_form
MyFormSetClass = Author_formset
fieldName = "authors"
def DoStuff(model_id=None):
if (model_id):
model = MyModelClass.objects.get(pk=model_id)
else:
model = MyModelClass()
form = MyFormClass(instance=model)
if model.pk:
m2mModels = getattr(model,fieldName)
formset = MyFormSetClass(queryset = m2mModels.all())
else:
m2mModelClass = MyFormSetClass.form.Meta.model
formset = MyFormSetClass(queryset = m2mModelClass.objects.none())
This seems a bit ugly, but it works.
OTHER TIPS
You're on the right track.
book.authors
is the queryset of "authors for which there is a m2m from this book". So that is perfectly valid to pass into the formset init.
formset = AuthorFormset(queryset=m2m_field.all())