Code: my categories

#django

#python

#tutorials

#web

18 Sep, 2005 - 2 minutes

After some requests I decided to publish my code for categories. It’s very simple. It was inspired by following articles: A "category" Data Model (note: this article uses old-style model format, it doesn’t work anymore) and Relating an object to itself, many-to-one .

from django.core import meta

class Category(meta.Model):
    """
    Category defines following fields:

    name        - simple name of category, e.g., 'C++'
    full_name   - full name of category, which includes names of all parents,
                  e.g. 'Development::C++'
    parent      - reference to parent category or null
    description - HTML description of category, or null

    Notes:

    1) full_name is not editable. It is calculated automatically
       by calculate_full_name() method during save phase (hook _pre_save).
    2) Separator specified by get_separator() method. It can be
       overridden in subclasses.
    """
    name        = meta.CharField(maxlength=50)
    full_name   = meta.CharField(maxlength=250, unique=True,
                                 editable=False)
    parent      = meta.ForeignKey('self', blank=True, null=True,
                                  related_name='child')
    description = meta.TextField(blank=True, null=True,
                                 help_text="Use raw HTML.")

    class META:
        verbose_name_plural = 'Categories'
        module_name = verbose_name_plural.lower()
        admin = meta.Admin(
            list_display  = ('full_name',),
            search_fields = ['full_name',],
            js = (
                '/tiny_mce/tiny_mce.js',
                '/appmedia/admin/js/textareas.js',
            ),
        )
        ordering = ('full_name',)

    def __repr__(self):
        return self.full_name

    def _pre_save(self):
        self.full_name = self.calculate_full_name()

    def get_separator(self):
        return '::'

    # note: used in templates
    def get_all_children(self):
        "get list of all children of the category"
        output = []
        children = self.get_child_list()
        for c in children:
            output.append(c)
            output.extend(c.get_all_children())
        return output

    # note: the last object of the list is the category itself
    # note: used in templates
    def get_all_parents(self):
        "get list of all parents of the category from top level parent down"
        id_list = []
        object = self
        while True:
            id_list.append(object)
            if not object.parent_id:
                break
            object = object.get_parent()
        id_list.reverse()
        return id_list

    # note: used in templates
    def calculate_full_name(self):
        "calculate full name from parent list"
        return self.get_separator().join([x.name for x in self.get_all_parents()])

    # note: used in templates
    def get_path(self):
        "get relative path of the category"
        return 'categories/%d/' % self.id

As you can see it is very simple. This model defines full_name field, which is auto-populated. I was toying with an idea to keep parent_name and produce full_name by concatenating parent_name with name. But after some trials I decided against it: it introduced a lot of complexities and runtime overhead by saving a few bytes in database. In my opinion it doesn’t worth it. This model defines some convenience methods as well. They are meant to be used in templates.

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