CODEWITHSUNDEEP
pythondjangodjango-models
Peter
Peter

Reputation: 312

Sorting ForiegnKey Objects in Django

I have a model that has two main classes.

The first is the book model and the second is the page model

The pages have a foreign key field to the books which lets me access them but what I am curious about is, how would you implement page numbers such that when creating a new page object, the number is limited only to be within the current length of pages? Furthermore, if it is inserted, how would you shift the following pages down one in number?

Right now I just have an integer field that I manually type in the page number but if I want to allow users to add pages themselves later, that won't do.

UPDATED:

class Textbook(models.Model):
    founder = models.CharField(max_length=256)
    title = models.CharField(max_length=256)
    cover = models.ImageField(upload_to=get_image_path, 
                              blank=True, 
                              null=True)

    def __str__(self):
        return self.title


class Page(models.Model):
    textbook = models.ForeignKey(Textbook, related_name="pages")
    page_title = models.CharField(max_length = 256)

    def __str__(self):
        return self.page_title


class Section(models.Model):
    page = models.ForeignKey(Page,related_name="sections")
    section_title = models.CharField(max_length=256)
    text = RichTextField(config_name='awesome_ckeditor')

    def __str__(self):
        return self.section_title

So above is my model, what I am trying to do is make it so that you can keep track of pages, which are contained in TextBooks, in order. Furthermore, you can insert a new page and the page numbers will change accordingly. So if you say have pages 1,2,3 and want to add a new one, you can add a new one as page 4, or insert it in between 2 and 3 and the former page 3 becomes page 4.

Upvotes: 2

Views: 62

Answers (2)

Nafiul Islam
Nafiul Islam

Reputation: 82450

This is a rather improvised solution that I came up with a long time ago, but you might give it a go. What you can do is to use a CharField.

So for example, you have a book with the following pages:

1 1.1 2 2.1 2.11 2.111 3 4 5 6 7 8.11

When you insert a new page into the book just add another 1 to the end of the page number or decimal field. Then you can just occasionally run a maintenance task to just clean up all the numbers back to 1 2 3 4, so that you can routinely discard the extra decimals.

You can take a look at the following python code:

In [2]: l
Out[2]: ['1', '2', '3', '4', '4.1', '4.11', '4.11', '5', '6', '1.1']

In [3]: sorted(l)
Out[3]: ['1', '1.1', '2', '3', '4', '4.1', '4.11', '4.11', '5', '6']

In [4]: l.append('5.1')

In [5]: sorted(l)
Out[5]: ['1', '1.1', '2', '3', '4', '4.1', '4.11', '4.11', '5', '5.1', '6']

You can create a routine task, using a django management command to run every once in a while in the background.

Upvotes: 0

encolpe
encolpe

Reputation: 311

Does the 'order_with_respect' option the answer at your question:

https://docs.djangoproject.com/en/1.10/ref/models/options/#order-with-respect-to

Upvotes: 1

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