Question

Let’s say I have some contrived models:

class Author(Model):    name = CharField()  class Book(Model):    title = CharField()    author = ForeignKey(Author) 

And let’s say I want to use a ModelForm for Book:

   class BookForm(ModelForm):       class Meta:          model = Book 

Simple so far. But let’s also say that I have a ton of Authors in my database, and I don’t want to have such a long multiple choice field. So, I’d like is to restrict the queryset on the BookForm’s ModelMultipleChoiceField author field. Let’s also say that the queryset I want can’t be chosen until __init__, because it relies on an argument to be passed.

This seems like it might do the trick:

class BookForm(ModelForm):    class Meta:       model = Book     def __init__(self, letter):       # returns the queryset based on the letter       choices = getChoices(letter)       self.author.queryset = choices 

Of course, if that just worked I wouldn’t be here. That gets me an AttributeError. ‘BookForm’ object has no attribute ‘author’. So, I also tried something like this, where I try to override the ModelForm’s default field and then set it later:

class BookForm(ModelForm):    author = ModelMultipleChoiceField(queryset=Author.objects.all())     class Meta:       model = Book     def __init__(self, letter):       choices = getChoices(letter)       self.author.queryset = choices 

Which produces the same result.

Anyone know how this is intended to be done?

Answer 1

Form objects don’t have their fields as attributes, you need to look in the ‘fields’ attribute, which is a dictionary:

self.fields['author'].queryset = choices 

If you want to fully understand what’s going on here, you might be interested in this answer – it’s about Models, but Forms work similarly.