From 28181e4d0556369aa673ae90f10e1c890797bde4 Mon Sep 17 00:00:00 2001
From: Stephen Burrows <stephen.r.burrows@gmail.com>
Date: Mon, 27 Sep 2010 17:42:47 -0400
Subject: [PATCH] Added methods and functions to support syncing embedded
 models in post-save.

---
 contrib/penfield/embed.py              | 70 ++++++++++++++++++--------
 contrib/penfield/templatetags/embed.py |  1 -
 2 files changed, 48 insertions(+), 23 deletions(-)

diff --git a/contrib/penfield/embed.py b/contrib/penfield/embed.py
index b279fc7..ea0199f 100644
--- a/contrib/penfield/embed.py
+++ b/contrib/penfield/embed.py
@@ -32,7 +32,48 @@ class TemplateField(models.TextField):
 		return Template(value)
 
 
+class Embed(models.Model):
+	embedder_content_type = models.ForeignKey(ContentType, related_name="embedder_related")
+	embedder_object_id = models.PositiveIntegerField()
+	embedder = generic.GenericForeignKey("embedder_content_type", "embedder_object_id")
+	
+	embedded_content_type = models.ForeignKey(ContentType, related_name="embedded_related")
+	embedded_object_id = models.PositiveIntegerField()
+	embedded = generic.GenericForeignKey("embedded_content_type", "embedded_object_id")
+	
+	def delete(self):
+		# Unclear whether this would be called by a cascading deletion.
+		super(Embed, self).delete()
+		# Cycle through all the fields in the embedder and remove all references to the embedded object.
+	
+	def get_embed_tag(self):
+		"""Convenience function to construct the embed tag that would create this instance."""
+		ct = self.embedded_content_type
+		return "{%% embed %s.%s %s %%}" % (ct.app_label, ct.model, self.embedded_object_id)
+	
+	class Meta:
+		app_label = 'penfield'
+
+
+def sync_embedded_objects(model_instance, embedded_instances):
+	# First, fetch all current embeds.
+	model_instance_ct = ContentType.objects.get_for_model(model_instance)
+	current_embeds = Embed.objects.filter()
+	
+	new_embed_pks = []
+	for embedded_instance in embedded_instances:
+		embedded_instance_ct = ContentType.objects.get_for_model(embedded_instance)
+		new_embed = Embed.objects.get_or_create(embedder_content_type=model_instance_ct, embedder_object_id=model_instance.id, embedded_content_type=embedded_instance_ct, embedded_object_id=embedded_instance.id)[0]
+		new_embed_pks.append(new_embed.pk)
+	
+	# Then, delete all embed objects related to this model instance which do not relate
+	# to one of the embedded instances.
+	Embed.objects.filter(embedder_content_type=model_instance_ct, embedder_object_id=model_instance.id).exclude(pk__in=new_embed_pks).delete()
+
+
 class EmbedField(TemplateField):
+	_embedded_instances = set()
+	
 	def validate_template(self, template):
 		"""Check to be sure that the embedded instances and templates all exist."""
 		for node in template.nodelist:
@@ -47,30 +88,15 @@ class EmbedField(TemplateField):
 					embedded_template = loader.get_template(node.template_name)
 					self.validate_template(embedded_template)
 				elif node.object_pk is not None:
-					embedded_instance = node.model.objects.get(pk=node.object_pk)
-	
-	def to_template(self, value):
-		return Template("{% load embed %}" + value)
-
-
-class Embed(models.Model):
-	embedder_embed_field = models.CharField(max_length=255)
-	
-	embedder_contenttype = models.ForeignKey(ContentType, related_name="embedder_related")
-	embedder_object_id = models.PositiveIntegerField()
-	embedder = generic.GenericForeignKey("embedder_contenttype", "embedder_object_id")
-	
-	embedded_contenttype = models.ForeignKey(ContentType, related_name="embedded_related")
-	embedded_object_id = models.PositiveIntegerField()
-	embedded = generic.GenericForeignKey("embedded_contenttype", "embedded_object_id")
+					self._embedded_instances.add(node.model.objects.get(pk=node.object_pk))
 	
-	def delete(self):
-		# Unclear whether this would be called by a cascading deletion.
-		
-		super(Embed, self).delete()
+	#def to_template(self, value):
+	#	return Template("{% load embed %}" + value)
 	
-	class Meta:
-		app_label = 'penfield'
+	def pre_save(self, model_instance, add):
+		if not hasattr(model_instance, '_embedded_instances'):
+			model_instance._embedded_instances = set()
+		model_instance._embedded_instances |= self._embedded_instances
 
 
 class Test(models.Model):
diff --git a/contrib/penfield/templatetags/embed.py b/contrib/penfield/templatetags/embed.py
index abdb1de..f8ab3f0 100644
--- a/contrib/penfield/templatetags/embed.py
+++ b/contrib/penfield/templatetags/embed.py
@@ -9,7 +9,6 @@ register = template.Library()
 class EmbedNode(template.Node):
 	def __init__(self, model, varname, object_pk=None, template_name=None):
 		assert template_name is not None or object_pk is not None
-		
 		app_label, model = model.split('.')
 		self.model = ContentType.objects.get(app_label=app_label, model=model).model_class()
 		self.varname = varname
-- 
2.20.1