Hi Germano,
When you use "ManyToMany", you're saying "any book can have any chapter and
vice versa". That's obviously what you don't want. What you want is "A book
has a closed set of chapters". This is done by thinking a bit on the other
way with Django: Instead of saying "There is a list of chapters of this
book", you say "The chapter belongs to a single book" with a foreign key:
class Book(models.Model):
title = models.CharField(max_length=250)
class Chapters(models.Model):
title = models.CharField(max_length=250)
text = models.TextField()
book = models.ForeignKey(Book)
Now a chapter can belong only to a book.
On Thu, Aug 9, 2018 at 4:34 PM, Germano Carella <germano.care...@gmail.com>
wrote:
> Hi,
> I'm Germano from Italy. I'm new of django.
> Probably this discussion has many many examples, but I can't find
> my situation.
> I have two models, Book and Chapters.
> These are simple models, I need them only for educational purpose.
>
> class Book(models.Model):
> title=models.CharField(max_length=250)
> chapters = models.ManyToManyField('Chapters')
>
> class Chapters(models.Model):
> title_of_chapter = models.CharField(max_length=250)
> text=models.TextField()
>
> Now, in admin interface I can add chapters on a new book and it works fine.
> So, whdn I try to add a second book I can see chapters of book I added
> previously.
>
> When I add a new book I want see only chapter of this book. List must be
> empty if I'm adding a new book.
> It's very simple, but I can't find a way to make it working.
>
> I tried somethings, such as
> chapters= models.ManyToManyField('Chapters',limit_choices_to=Q('
> book__title'=title))
> But this not works.
> I know Chapters has book_set, that is the set of references for a chapter.
>
> There is a way to make it working?
>
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