[Wagtail] Create pages in migrations

README.md

Unfortunately because models returned by apps.get_model in migrations aren't the actual class, methods like Page.add aren't available and we have to do it manually. The most sensitive part being the handling of the path.

As an aside, deleting pages in migration will not update the numchild of the parent page. Unfortunately, the fixtree command doesn't play nice within a migration so it will need to be ran separately (or the parent page should manually be updated).

Notes: When not within a migration, a page path could be created with parent_page.get_last_child()._inc_path() or Page._get_children_path_interval(parent_page.path)[1].

migration.py

from django.db import migrations
from treebeard.numconv import NumConv


# Values as of treebeard 4.2.0
PATH_ALPHABET = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'
PATH_STEP_LENGTH = 4
PATH_NUM_CONV_BASE_FUNC = NumConv(len(PATH_ALPHABET), PATH_ALPHABET).int2str


def path_num_conv(num):
    return PATH_NUM_CONV_BASE_FUNC(num).rjust(PATH_STEP_LENGTH, '0')


def add_child(apps, parent_page, klass, **kwargs):
    """
    Replicate `Page.add_child` in migrations since it is not available in this context.

    Originaly from http://www.agilosoftware.com/blog/django-treebard-and-wagtail-page-creation/
    with a fix for the path.
    """

    content_type_class = apps.get_model('contenttypes.ContentType')
    page_content_type = content_type_class.objects.get(
        model=klass.__name__.lower(),
        app_label=klass._meta.app_label
    )

    url_path = '%s%s/' % (parent_page.url_path, kwargs.get('slug'))
    path = parent_page.path + path_num_conv(parent_page.numchild + 1)

    created_page = klass.objects.create(
        content_type=page_content_type,
        path=path,
        depth=parent_page.depth + 1,
        numchild=0,
        url_path=url_path,
        **kwargs
    )

    parent_page.numchild += 1
    parent_page.save()

    return created_page


def forwards(apps, schema_editor):
    homepage_class = apps.get_model('core.HomePage')
    homepage = homepage_class.objects.get()

    mypage_class = apps.get_model('core.MyPage')
    mypage = add_child(apps, homepage, mypage_class, title='FooBarBaz', slug='foobarbaz')


class Migration(migrations.Migration):
    dependencies = [
        ...
    ]

    operations = [
        migrations.RunPython(forwards, migrations.RunPython.noop),
    ]