JSON .Net not respecting PreserveReferencesHandling on Deserialization

Question

I have doubly linked list that I am trying to deserialise.

My scenario closely relates to this SO: Doubly Linked List to JSON

I have the following JSON setti

Answer 1

Here is what I tried and worked fine:

The classes

public class TemplateDataLinkedListBase<T> where T : TemplateDataLinkedListBase<T>
{
    [JsonProperty(TypeNameHandling = TypeNameHandling.Objects)]
    public T Parent { get; set; }

    [JsonProperty(TypeNameHandling = TypeNameHandling.Objects)]
    public List<T> Children { get; set; }
}

public class TemplateDataQueryElement : TemplateDataLinkedListBase<TemplateDataQueryElement>
{
    public string Query { get; set; }

    public TemplateDataQueryElement()
    {
        Children = new List<TemplateDataQueryElement>();
    }
}

Initialization

var childLowest = new TemplateDataQueryElement
{
    Query = "Lowest"
};

var childMiddle = new TemplateDataQueryElement
{
    Query = "Middle",
    Children = new List<TemplateDataQueryElement>
    {
        childLowest
    }
};

childLowest.Parent = childMiddle;

var parent = new TemplateDataQueryElement
{
    Query = "Parent",
    Children = new List<TemplateDataQueryElement>
    {
        childMiddle
    }
};

childMiddle.Parent = parent;

Serialization settings

var _jsonSettings = new JsonSerializerSettings()
{
    TypeNameHandling = TypeNameHandling.Auto,
    ConstructorHandling = ConstructorHandling.AllowNonPublicDefaultConstructor,
    PreserveReferencesHandling = PreserveReferencesHandling.Objects,
    ObjectCreationHandling = ObjectCreationHandling.Auto
};

Serialization

var serializedStr = JsonConvert.SerializeObject(parent, Formatting.Indented, _jsonSettings);

The serialized json looks like this:

{
  "$id": "1",
  "Query": "Parent",
  "Parent": null,
  "Children": [
    {
      "$id": "2",
      "Query": "Middle",
      "Parent": {
        "$ref": "1"
      },
      "Children": [
        {
          "$id": "3",
          "Query": "Lowest",
          "Parent": {
            "$ref": "2"
          },
          "Children": []
        }
      ]
    }
  ]
}

Deserialization

var deserializedStructure = JsonConvert.DeserializeObject<TemplateDataQueryElement>(serializedStr, _jsonSettings);

The references in the deserializedStructure are preserved correctly.

Demo https://dotnetfiddle.net/j1Qhu6

UPDATE 1

The reason my example works, and the code you posted in the additional links doesn't is because my classes contain default constructor, and yours don't. Analyzing your classes, adding a default constructor to them, it won't break the functionality and the deserialization will be successful with Parent property initialized correctly. So what you basically need to do is add a default constructor to both classes:

public class TemplateDataLinkedListBase<T> where T : TemplateDataLinkedListBase<T>
{
    [JsonProperty(TypeNameHandling = TypeNameHandling.Objects)]
    public T Parent { get; set; }

    [JsonProperty(TypeNameHandling=TypeNameHandling.Objects)]
    public List<T> Children { get; set; }
    public string EntityName { get; set; }
    public HashSet<string> Fields { get; set; }

    public string Key { get { return getKey(); } }


    public TemplateDataLinkedListBase()
    {
        Children = new List<T>();
        Fields = new HashSet<string>();
    }

    public TemplateDataLinkedListBase(string entityName)
    {
        EntityName = entityName;
        Children = new List<T>();
        Fields = new HashSet<string>();
    }

    private string getKey()
    {
        List<string> keys = new List<string>();
        keys.Add(this.EntityName);
        getParentKeys(ref keys, this);
        keys.Reverse();
        return string.Join(".", keys);

    }

    private void getParentKeys(ref List<string> keys, TemplateDataLinkedListBase<T> element)
    {
        if (element.Parent != null)
        {
            keys.Add(element.Parent.EntityName);
            getParentKeys(ref keys, element.Parent);
        }
    }

    public T AddChild(T child)
    {
        child.Parent = (T)this;
        Children.Add(child);
        return (T)this;
    }

    public T AddChildren(List<T> children)
    {
        foreach (var child in children)
        {
            child.Parent = (T)this;
        }
        Children.AddRange(children);
        return (T)this;
    }

    public void AddFields(IEnumerable<string> fields)
    {
        foreach (var field in fields)
            this.Fields.Add(field);
    }

    public TemplateDataLinkedListBase<T> Find(string searchkey)
    {
        if (this.Key == searchkey)
        {
            return this;
        }
        else
        {
            foreach (var child in Children)
            {
                if (child.Key == searchkey)
                {
                    return child;
                }
                else
                {
                    var childResult = child.Find(searchkey);
                    if (childResult != null) return childResult;
                }
            }
        }
        return null;
    }
}

public class TemplateDataQueryElement : TemplateDataLinkedListBase<TemplateDataQueryElement>, ITemplateDataQueryElement
{
    public string TemplateModelName { get; set; }
    public string RecordId { get; set; }
    public string ParentForeignKeyName { get; set; }
    public string Query { get; set; }
    public dynamic ObjectData { get; set; }
    public ITemplateDataParseResult ParseResult { get; set; }


    public TemplateDataQueryElement() : base()
    {
        Fields.Add("Id"); //Always retrieve Id's
        ObjectData = new ExpandoObject();
    }

    public TemplateDataQueryElement(string entityName)
        : base(entityName)
    {
        Fields.Add("Id"); //Always retrieve Id's
        ObjectData = new ExpandoObject();
    }

    public override string ToString()
    {
        return string.Format("{0}: {1}", EntityName, Query);
    }
}

The EntityName property which you set through your constructor, will be deserialized correctly, since it is a public property.