NotesPage code

class NotesPage(Page):
    date = models.DateField("Post date")
    intro = models.CharField(max_length=250)
    #body = RichTextField(blank=True)
    tags = ClusterTaggableManager(through=NotePageTag, blank=True)
    categories = ParentalManyToManyField('study_notes.NoteCategory', blank=True)

    body = StreamField([
        ('heading', CharBlock(form_classname="title")),
        ('paragraph', RichTextBlock()),
        ('image', ImageChooserBlock()),
        ('code', CodeBlock(label="Code")),
        ('equation', MathBlock())
    ], use_json_field=True)


    search_fields = Page.search_fields + [
        index.SearchField('intro'),
        index.SearchField('body'),
    ]

    content_panels = Page.content_panels + [
        MultiFieldPanel([
            FieldPanel('date'),
            FieldPanel('tags'),
            FieldPanel('categories', widget=forms.CheckboxSelectMultiple),
        ], heading="Note information"),
        FieldPanel('intro'),
        FieldPanel('body'),
        InlinePanel('gallery_images', label="Gallery images"),
    ]

    def get_context(self, request):
        # Update context to include only published posts, ordered by reverse-chron
        context = super().get_context(request)
        context.update(BASE_CONTEXT)

        return context

    def main_image(self):
        gallery_item = self.gallery_images.first()
        if gallery_item:
            return gallery_item.image
        else:
            return None