Implement get_model / get_instance on link/embed handlers

wagtail/core/rich_text/__init__.py

@@ -1,3 +1,4 @@
+from django.db.models import Model
 from django.utils.safestring import mark_safe
 
 from wagtail.core.rich_text.feature_registry import FeatureRegistry
@@ -50,3 +51,41 @@ class RichText:
     def __bool__(self):
         return bool(self.source)
     __nonzero__ = __bool__
+
+
+class EntityHandler:
+    """
+    An 'entity' is a placeholder tag within the saved rich text, which needs to be rewritten
+    into real HTML at the point of rendering. Typically (but not necessarily) the entity will
+    be a reference to a model to be fetched to have its data output into the rich text content
+    (so that we aren't storing potentially changeable data within the saved rich text).
+
+    An EntityHandler defines how this rewriting is performed.
+
+    Currently Wagtail supports two kinds of entity: links (represented as <a linktype="...">...</a>)
+    and embeds (represented as <embed embedtype="..." />).
+    """
+    @staticmethod
+    def get_model():
+        return NotImplementedError
+
+    @classmethod
+    def get_instance(cls, attrs: dict) -> Model:
+        model = cls.get_model()
+        return model._default_manager.get(id=attrs['id'])
+
+    @staticmethod
+    def expand_db_attributes(attrs: dict) -> str:
+        """
+        Given a dict of attributes from the entity tag
+        stored in the database, returns the real HTML representation.
+        """
+        raise NotImplementedError
+
+
+class LinkHandler(EntityHandler):
+    pass
+
+
+class EmbedHandler(EntityHandler):
+    pass

wagtail/core/rich_text/pages.py

@@ -1,13 +1,22 @@
 from django.utils.html import escape
 
 from wagtail.core.models import Page
+from wagtail.core.rich_text import LinkHandler
 
 
-class PageLinkHandler:
+class PageLinkHandler(LinkHandler):
     @staticmethod
-    def expand_db_attributes(attrs):
+    def get_model():
+        return Page
+
+    @classmethod
+    def get_instance(cls, attrs):
+        return super().get_instance(attrs).specific
+
+    @classmethod
+    def expand_db_attributes(cls, attrs):
         try:
-            page = Page.objects.get(id=attrs['id'])
+            page = cls.get_instance(attrs)
             return '<a href="%s">' % escape(page.specific.url)
         except Page.DoesNotExist:
             return "<a>"

wagtail/documents/rich_text/__init__.py

@@ -1,16 +1,21 @@
+from django.core.exceptions import ObjectDoesNotExist
 from django.utils.html import escape
 
+from wagtail.core.rich_text import LinkHandler
 from wagtail.documents.models import get_document_model
 
 
 # Front-end conversion
 
-class DocumentLinkHandler:
+class DocumentLinkHandler(LinkHandler):
     @staticmethod
-    def expand_db_attributes(attrs):
-        Document = get_document_model()
+    def get_model():
+        return get_document_model()
+
+    @classmethod
+    def expand_db_attributes(cls, attrs):
         try:
-            doc = Document.objects.get(id=attrs['id'])
+            doc = cls.get_instance(attrs)
             return '<a href="%s">' % escape(doc.url)
-        except (Document.DoesNotExist, KeyError):
+        except (ObjectDoesNotExist, KeyError):
             return "<a>"

wagtail/embeds/rich_text/__init__.py

@@ -1,9 +1,20 @@
+from wagtail.core.rich_text import EmbedHandler
 from wagtail.embeds import format
+from wagtail.embeds.embeds import get_embed
+from wagtail.embeds.models import Embed
 
 
 # Front-end conversion
 
-class MediaEmbedHandler:
+class MediaEmbedHandler(EmbedHandler):
+    @staticmethod
+    def get_model():
+        return Embed
+
+    @staticmethod
+    def get_instance(attrs):
+        return get_embed(attrs['url'])
+
     @staticmethod
     def expand_db_attributes(attrs):
         """

wagtail/images/rich_text/__init__.py

@@ -1,20 +1,26 @@
+from django.core.exceptions import ObjectDoesNotExist
+
+from wagtail.core.rich_text import EmbedHandler
 from wagtail.images import get_image_model
 from wagtail.images.formats import get_image_format
 
 
 # Front-end conversion
 
-class ImageEmbedHandler:
+class ImageEmbedHandler(EmbedHandler):
     @staticmethod
-    def expand_db_attributes(attrs):
+    def get_model():
+        return get_image_model()
+
+    @classmethod
+    def expand_db_attributes(cls, attrs):
         """
         Given a dict of attributes from the <embed> tag, return the real HTML
         representation for use on the front-end.
         """
-        Image = get_image_model()
         try:
-            image = Image.objects.get(id=attrs['id'])
-        except Image.DoesNotExist:
+            image = cls.get_instance(attrs)
+        except ObjectDoesNotExist:
             return "<img>"
 
         image_format = get_image_format(attrs['format'])