CODEWITHSUNDEEP
pythondjango
zhuyxn
zhuyxn

Reputation: 7081

Django: Create Submodel in Model

Suppose I have two models, Book and Page, such there is a one-to-many relationship between Page to Book. I would like each Book model, to have a function which creates a bunch of Pages for the respective Book model, but I'm not sure how to associate each Page's foreign key back to the Book instance it was created in.

I currently have an associate function, which finds the correct book amongst all the possible books, and I'm sure there's a better way, but I can't seem to find it. Is it possible to set the foreignkey to self?

Upvotes: 1

Views: 6276

Answers (3)

Skylar Saveland
Skylar Saveland

Reputation: 11464

class Page(models.Model):
    # default related_name would be `page_set` but `pages`
    # seems a bit more intuitive, your choice.
    book = models.ForeignKey("yourapp.Book", related_name="pages")


class Book(models.Model):
    # ...

    # you can use self as the instance and magically you have
    # this `pages` attr which is a related manager, like `Page.objects`
    # but limited to the particular Book's pages.
    def special_page_create(self, *args, **kwargs):
        self.pages.create(
            # ...
        )
        # ...

then, you have a book instance, you have a related manager, 

book = Book.objects.get(...
book.pages.create(...
page, created = book.pages.get_or_create(...
pages_gte_42 = book.pages.filter(num__gte=42)
# etc

let me know what else you need to know. The reverse relationship is semi-magical; you don't declare anything on the Book class but you get the related manager on the Book instances.

Upvotes: 4

Hans Then
Hans Then

Reputation: 11322

There is a one-to-many relationship between Book and Page. This means that one Book has several Pages and each Page only one Book.

In a database (and therefore in an ORM mapper) you would model this by creating a foreign key in Page. This foreign key would point to the Book instance that contains these Pages.

If you want to find the Pages for a Book, you'd query the Pages table for all Pages with the same foreign key as the primary key of the Book.

Upvotes: 1

K-man
K-man

Reputation: 364

would try something like this:

Class Page(models.Model):
    #Your fields, like a name or whatever
    name = models.CharField(max_length=60)

    Book= models.ForeignKey("Book")


Class Book(models.Model):
    #Your fields again       

    def create_page(self):
        "Adds a page to the book"
        #Do what you need to do
        page = Page(name="TitlePage", Book=self)
        page.save()

Or something like that... I think the order of the classes is important too.

Upvotes: 2

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