From 3694756e4e7ec1f3fa095e0e61526c83319c821b Mon Sep 17 00:00:00 2001
From: Matt Westcott <matt@west.co.tt>
Date: Wed, 14 Jan 2015 20:55:25 +0000
Subject: [PATCH] try to implement to_python and get_prep_value; run into
 awkward discrepancies between renderable and JSON-ish values

---
 wagtail/wagtailadmin/widgets.py |  4 ++--
 wagtail/wagtailcore/fields.py   | 17 ++++++++++++++++-
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/wagtail/wagtailadmin/widgets.py b/wagtail/wagtailadmin/widgets.py
index b5889de7a..0f2fc7f85 100644
--- a/wagtail/wagtailadmin/widgets.py
+++ b/wagtail/wagtailadmin/widgets.py
@@ -62,7 +62,7 @@ class StreamWidget(widgets.Widget):
         self.block_def = block_def
 
     def render(self, name, value, attrs=None):
-        bound_block = self.block_def.bind(json.loads(value), prefix=name)
+        bound_block = self.block_def.bind(value, prefix=name)
         js_initializer = self.block_def.js_initializer()
         if js_initializer:
             js_snippet = """
@@ -82,4 +82,4 @@ class StreamWidget(widgets.Widget):
         return self.block_def.all_media()
 
     def value_from_datadict(self, data, files, name):
-        return json.dumps(self.block_def.value_from_datadict(data, files, name))
+        return self.block_def.value_from_datadict(data, files, name)
diff --git a/wagtail/wagtailcore/fields.py b/wagtail/wagtailcore/fields.py
index a459d6071..82d6a4905 100644
--- a/wagtail/wagtailcore/fields.py
+++ b/wagtail/wagtailcore/fields.py
@@ -4,9 +4,11 @@ import json
 
 from django.db import models
 from django.forms import Textarea
+from django.utils.six import with_metaclass
 
 from wagtail.wagtailcore.rich_text import DbWhitelister, expand_db_html
 from wagtail.utils.widgets import WidgetWithScript
+from wagtail.wagtailadmin.blocks import StreamBlock  # FIXME: wagtailcore shouldn't be depending on wagtailadmin
 
 
 class RichTextArea(WidgetWithScript, Textarea):
@@ -38,12 +40,25 @@ class RichTextField(models.TextField):
         return super(RichTextField, self).formfield(**defaults)
 
 
-class StreamField(models.TextField):
+class StreamField(with_metaclass(models.SubfieldBase, models.TextField)):
     def __init__(self, block_types, **kwargs):
         self.block_types = block_types
+        self.stream_block = StreamBlock(block_types)
         super(StreamField, self).__init__(**kwargs)
 
     def deconstruct(self):
         name, path, args, kwargs = super(StreamField, self).deconstruct()
         kwargs['block_types'] = self.block_types
         return name, path, args, kwargs
+
+    def to_python(self, value):
+        if value is None:
+            return []
+        elif isinstance(value, list):
+            return value
+        else:  # assume string
+            return self.stream_block.renderable(json.loads(value))
+
+    def get_prep_value(self, value):
+        return json.dumps(value)
+