New member: Germano Carella. I need help with django, limit_choices_to and admin interface

[Germano Carella]

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? 

[Julio Biason]

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.

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[germano carella]

Hi Julio,

Thanks, now is clear.

Ok, I created models correctly and createa book in admin interface. Now I can create chapters to add this book.

Now I want to learn how to create an interface that allows an user to add a new book, click on next button and add chapters to this book that is selected by default in book select list.

Can you point me in a tutorial, or document?

Thanks in advance,

Germano

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[germano carella]

I found a tutorial!

I studied ForeignKey and how it works with sets... Now, I'll learn how to create a form and how to save the new data in set.

Thanks!

Il 09/08/2018 22:59, Julio Biason ha scritto:

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