models.py

from django.db import models
from django.utils.translation import ugettext_lazy as _
from django.utils.encoding import python_2_unicode_compatible

from modelcluster.models import ClusterableModel
from modelcluster.fields import ParentalKey

from wagtail.wagtailcore.models import Orderable
from wagtail.wagtailadmin.edit_handlers import FieldPanel, InlinePanel
from wagtail.wagtailimages.edit_handlers import ImageChooserPanel
from wagtail.wagtailsnippets.models import register_snippet


class GalleryItem(models.Model):
    image = models.ForeignKey(
        'wagtailimages.Image', null=True, blank=True,
        on_delete=models.SET_NULL, related_name='+')
    source = models.CharField(
        max_length=255, verbose_name=_('Source'),
        help_text=_('Author/Origin of an image.'))
    alt_text = models.CharField(
        max_length=255, blank=True, default='',
        help_text=_('Text displayed in image alt tag.'))
    description = models.CharField(
        max_length=255, blank=True, default='',
        help_text=_('Short description of an image'))

    panels = [
        ImageChooserPanel('image'),
        FieldPanel('source'),
        FieldPanel('alt_text'),
        FieldPanel('description')
    ]

    class Meta:
        abstract = True


class GallerySnippetGalleryItems(Orderable, GalleryItem):
    item = ParentalKey(
        'galleries.GallerySnippet', related_name='related_gallery_items')


@python_2_unicode_compatible
@register_snippet
class GallerySnippet(ClusterableModel):
    title = models.CharField(max_length=80, verbose_name=_('Gallery title'))
    created_at = models.DateField(verbose_name=_('Date created'))
    panels = [
        FieldPanel('title', classname='col8'),
        FieldPanel('created_at', classname='col4'),
        InlinePanel('related_gallery_items', label='Item')
    ]

    def __str__(self):
        return self.title