Update predecessor properly

Fixes #25

program/serializers.py

@@ -237,6 +237,7 @@ class ShowSerializer(serializers.HyperlinkedModelSerializer):
     musicfocus = serializers.PrimaryKeyRelatedField(queryset=MusicFocus.objects.all(),many=True)
     type = serializers.PrimaryKeyRelatedField(queryset=Type.objects.all())
     fundingcategory = serializers.PrimaryKeyRelatedField(queryset=FundingCategory.objects.all())
+    predecessor = serializers.PrimaryKeyRelatedField(queryset=Show.objects.all(),required=False,allow_null=True)
     thumbnails = serializers.SerializerMethodField() # Read-only
 
     def get_thumbnails(self, show):
@@ -254,7 +255,7 @@ class ShowSerializer(serializers.HyperlinkedModelSerializer):
         model = Show
         fields = ('id', 'name', 'slug', 'image', 'ppoi', 'logo', 'short_description', 'description',
                   'email', 'website', 'created', 'last_updated', 'type', 'fundingcategory',
-                  'predecessor_id', 'cba_series_id', 'fallback_id', 'category', 'hosts',
+                  'predecessor', 'cba_series_id', 'fallback_id', 'category', 'hosts',
                   'owners', 'language', 'topic', 'musicfocus', 'thumbnails')
 
 
@@ -300,7 +301,6 @@ class ShowSerializer(serializers.HyperlinkedModelSerializer):
         instance.description = validated_data.get('description', instance.description)
         instance.email = validated_data.get('email', instance.email)
         instance.website = validated_data.get('website', instance.website)
-        instance.predecessor_id = validated_data.get('predecessor_id', instance.predecessor_id)
         instance.cba_series_id = validated_data.get('cba_series_id', instance.cba_series_id)
         instance.fallback_id = validated_data.get('fallback_id', instance.fallback_id)
 
@@ -314,6 +314,7 @@ class ShowSerializer(serializers.HyperlinkedModelSerializer):
             instance.musicfocus = validated_data.get('musicfocus', instance.musicfocus)
             instance.type = validated_data.get('type', instance.type)
             instance.fundingcategory = validated_data.get('fundingcategory', instance.fundingcategory)
+            instance.predecessor = validated_data.get('predecessor', instance.predecessor)
 
         instance.save()
         return instance