Hi

We have a bunch of propertylists in our project, all of which started throwing serialization errors post upgrade to CMS 12. Here's a detailed exception : 

Unexpected error when updating property groupsForNewsAudienceTargeting
Newtonsoft.Json.JsonReaderException: Unexpected character encountered while parsing value: [. Path '', line 1, position 1.
   at Newtonsoft.Json.JsonTextReader.ReadStringValue(ReadType readType)
   at Newtonsoft.Json.JsonTextReader.ReadAsString()
   at Newtonsoft.Json.JsonReader.ReadForType(JsonContract contract, Boolean hasConverter)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at EPiServer.Cms.Shell.UI.Rest.ContentChangeManager.Deserialize(String value, Type type)
   at EPiServer.Cms.Shell.UI.Rest.ContentChangeManager.UpdateProperties(IDictionary`2 properties, IContent content)
08/05/2022 12:22:49 An exception occurred while converting JSON property
Newtonsoft.Json.JsonReaderException: Unexpected character encountered while parsing value: [. Path '', line 1, position 1.
   at Newtonsoft.Json.JsonTextReader.ReadStringValue(ReadType readType)
   at Newtonsoft.Json.JsonTextReader.ReadAsString()
   at Newtonsoft.Json.JsonReader.ReadForType(JsonContract contract, Boolean hasConverter)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)

I compared our logic against Foundation for .net6 and its pretty much the same.

After much trial and error, when i deleted the old content type that had the propertylist on it in DB, and let the code recreate it at next launch, was I able to get these to work again. However, considering this is an existing live site going under the upgrade, deleting content types causes us to lose all content created for that type and will have to recreate it once new content type is in. 

I don't know if this issue is introduced by the .net core DB upgrade scripts or the internal library upgrades. But this is definitely a roadblock fo us to proceed.

Please advice on how to resolve this without losing content.

P.S. : On a side note, we ran into a similar serialization error with the new Episerver.Social packages and after opening a support ticket and escalations, that was identified as a bug in Episerver.Social and fixed. Could we maybe have a similar issue here in the Core packages?

Update :

Seeing this new exception today : 

08/09/2022 12:55:30 Detected change of type on property GroupsForNewsAudienceTargeting on AdSettings. Converting existing content of type EPiServer.Core.DefaultPropertyJson to new backing type NMIC02_DC.Features.Settings.AdGroupProperty is not possible without loss of data. No change is commited.

All I did was follow the recommendation in this thread : CollectionEditor not displaying items | Optimizely Developer Comm

So added this to my propertyList : 

[Display(Name = "AD groups for news audience targeting", Order = 10)]
        [EditorDescriptor(EditorDescriptorType = typeof(CollectionEditorDescriptor<AdGroup>))]
        [ClientEditor(ClientEditingClass = "nmic02/ADSettingsCollectionEditor")]
        public virtual IEnumerable<AdGroup> GroupsForNewsAudienceTargeting { get; set; }

 [PropertyDefinitionTypePlugIn]
    public class AdGroupProperty : PropertyList<AdGroup>
    {
        private Injected<ObjectSerializerFactory> _objectSerializerFactory;
        protected override AdGroup ParseItem(string value)
        {
            var objectSerializer = _objectSerializerFactory.Service.GetSerializer("application/json");
            return objectSerializer.Deserialize<AdGroup>(value);
        }
    }

    [PropertyDefinitionTypePlugIn]
    public class AdGroupValueProperty : PropertyList<AdGroupValue>
    {
        private Injected<ObjectSerializerFactory> _objectSerializerFactory;
        protected override AdGroupValue ParseItem(string value)
        {
            var objectSerializer = _objectSerializerFactory.Service.GetSerializer("application/json");
            return objectSerializer.Deserialize<AdGroupValue>(value);
        }
    }

Regards

Ritu