In [9]:

#r "nuget:Utf8Json"

using Utf8Json; 
using System.Runtime.Serialization;
using System.Collections.Generic;
using System.Collections.ObjectModel;

Installing package Utf8Json.....done!

Successfully added reference to package Utf8Json, version 1.3.7

In [13]:

public class Item 
{
    
    public string Name {get;set;}
    public int Value {get;set;}
    public double Weight {get;set;}
    [IgnoreDataMember]
    public ItemCollection Parent {get;set;}
}

public class ItemCollection : KeyedCollection<string, Item>
{
    protected override string GetKeyForItem(Item item) { return item.Name; }
}

var first = new Item() {Name = "ddd", Value = 5, Weight = 54.2}; 

Console.WriteLine( JsonSerializer.ToJsonString(first)); 

var Col = new ItemCollection(); 
Col.Add(first);

Console.WriteLine( JsonSerializer.ToJsonString(Col));

var ColDes =  JsonSerializer.Deserialize<ItemCollection>(JsonSerializer.ToJsonString(Col));

{"Name":"ddd","Value":5,"Weight":54.2}
[{"Name":"ddd","Value":5,"Weight":54.2}]

Unhandled Exception
The value "System.Collections.Generic.Dictionary`2[System.String,System.Object]" is not of type "Submission#14+Item" and cannot be used in this generic collection. (Parameter 'value')
   at System.Collections.ObjectModel.Collection`1.System.Collections.IList.Add(Object value)
   at Utf8Json.Formatters.NonGenericListFormatter`1.Deserialize(JsonReader& reader, IJsonFormatterResolver formatterResolver)
   at Utf8Json.JsonSerializer.Deserialize[T](Byte[] bytes, Int32 offset, IJsonFormatterResolver resolver)
   at Utf8Json.JsonSerializer.Deserialize[T](Byte[] bytes, IJsonFormatterResolver resolver)
   at Utf8Json.JsonSerializer.Deserialize[T](String json, IJsonFormatterResolver resolver)
   at Utf8Json.JsonSerializer.Deserialize[T](String json)
   at Submission#14.<<Initialize>>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.CodeAnalysis.Scripting.ScriptExecutionState.RunSubmissionsAsync[TResult](ImmutableArray`1 precedingExecutors, Func`2 currentExecutor, StrongBox`1 exceptionHolderOpt, Func`2 catchExceptionOpt, CancellationToken cancellationToken)

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