Serializing an Entity with Child Entities when saving session state.

Question

I have an Windows Store 8.1 app and I am trying to save the state during a suspend and shutdown.  I found these serialization functions:

        public static string SerializeObject(object obj)
        {
            MemoryStream stream = new MemoryStream();
            System.Runtime.Serialization.Json.DataContractJsonSerializer ser = new System.Runtime.Serialization.Json.DataContractJsonSerializer(obj.GetType(), Common.SuspensionManager.KnownTypes);
            ser.WriteObject(stream, obj);
            byte[] data = new byte[stream.Length];
            stream.Seek(0, SeekOrigin.Begin);
            stream.Read(data, 0, data.Length);
            return Convert.ToBase64String(data);
        }

        public static T DeserializeObject<T>(string input)
        {
            System.Runtime.Serialization.Json.DataContractJsonSerializer ser = new System.Runtime.Serialization.Json.DataContractJsonSerializer(typeof(T));
            MemoryStream stream = new MemoryStream(Convert.FromBase64String(input));
            return (T)ser.ReadObject(stream);
        }

They work well unless the Entity has Child Entities.  I am using Entity Framework and it Generates the Child Entities as DataServiceCollections.  These serialize fine, but when you resume the program and they get deserialized, you get the error:

An item could not be added to the collection. When items in a DataServiceCollection are tracked by the DataServiceContext, new items cannot be added before items have been loaded into the collection.

Serialization Function Call is:

e.PageState["SelectedEstimate"] = StringSerializer.SerializeObject(Est);

The deserialization call is:

Est = StringSerializer.DeserializeObject<Estimate>((string)e.PageState["SelectedEstimate"]);

The Est object is of type Estimate and it has several child collections which are created as type DataServiceCollection.  Is there a way to serialize these such that they can be deserialized without the error?

Any help would be greatly appreciated.

Jim

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Jim Wilcox

Answer 1

If you search on Deserialize JSON Nested classes you will see you simply define the nested classes.  Here is one example: http://social.msdn.microsoft.com/Forums/en-US/1b0b9a6e-5af1-4e84-aa8d-5db731adba93/how-to-serialize-a-class-with-nested-class?forum=csharplanguage

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Jeff Sanders (MSFT)

@jsandersrocks - Windows Store Developer Solutions @WSDevSol
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Answer 2

I added the types to the known types as you recommended but still no luck.

I think it has more to do with the fact that the Child collections are DataServiceCollections.

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Jim Wilcox