JSON.Net在反序列化时不尊重PreserveReferences处理

Question

我有一个双链表，我正在尝试取消序列化。

我的场景与这个SO:Doublely Linked List to JSON 密切相关

我有以下JSON设置：

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

当我看到串行化的输出时，它看起来是正确的，并且节点之间的引用得到了正确的表示。

当数据被取消序列化时，子对象中的Parent属性为null，即使它们正确地填充了$ref。

下面是JSON（为了可读性而剪裁）的示例

在输入这个问题的过程中，我可能已经看到了问题的根源。。。

"Children"数组属性中的对象没有$type属性。

这可能是因为Children和Parent属性属于泛型类型T。

请注意，被序列化的实际类型是TemplateDataLinkedListBase的派生类

public class TemplateDataQueryElement : TemplateDataLinkedListBase<TemplateDataQueryElement>

以下是基类的摘录：

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; }
}

如何以Parent属性不为null并包含对父对象的引用的方式取消序列化此JSON？

    {
    "$id": "9",
    "$type": "Contracts.Models.TemplateDataQueryElement, Contracts",
    "Query": null,
    "Parent": null,
    "Children": [
      {
        "$id": "11",
        "Query": null,
        "Parent": {
          "$ref": "9"
        },
        "Children": [
          {
            "$id": "13",
            "Query": null,
            "Parent": {
              "$ref": "11"
            },
            "Children": [],
            "EntityName": "Widgets",
            "Fields": [
              "Id"
            ],
            "Key": ""
          },

以下是相关代码的PasteBin链接：

http://pastebin.com/i1jxVGG3http://pastebin.com/T1xqEWW2http://pastebin.com/ha42SeF7http://pastebin.com/cezwZqx6http://pastebin.com/uFbTbUZehttp://pastebin.com/sRhNQgzh

Answer 1

以下是我尝试并运行良好的内容：

类

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>();
    }
}

初始化

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;

序列化设置

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

序列化

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

序列化的json如下所示：

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

反序列化

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

deserializedStructure中的引用被正确地保留。

演示https://dotnetfiddle.net/j1Qhu6

更新1

我的示例之所以有效，而您在附加链接中发布的代码却无效，是因为我的类包含默认构造函数，而您的类则不包含。分析你的类，为它们添加一个默认的构造函数，它不会破坏功能，并且在正确初始化Parent属性的情况下反序列化会成功。因此，您基本上需要做的是为这两个类添加一个默认构造函数：

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);
    }
}

通过构造函数设置的EntityName属性将被正确反序列化，因为它是公共属性。