c# - JSON .Net 在反序列化时不遵守 PreserveReferencesHandling

Question

我有一个双向链表，我正在尝试反序列化。

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

我有以下 JSON 设置:

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

当我查看序列化输出时，它看起来是正确的，并且节点之间的引用被正确表示。

当数据被反序列化时，子对象中的父属性为空，即使它们正确填充了 $ref。

下面是 JSON 的示例(为了便于阅读而进行了修剪)

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 属性是通用类型 T。

注意实际被序列化的类型是TemplateDataLinkedListBase的派生类

public class TemplateDataQueryElement : TemplateDataLinkedListBase<TemplateDataQueryElement>

这是基类的摘录:

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反序列化此 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/i1jxVGG3 http://pastebin.com/T1xqEWW2 http://pastebin.com/ha42SeF7 http://pastebin.com/cezwZqx6 http://pastebin.com/uFbTbUZe http://pastebin.com/sRhNQgzh

Answer 1

这是我尝试过的并且效果很好的方法:

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);

序列化后的 json 是这样的:

{
  "$id": "1",
  "Query": "Parent",
  "Parent": null,
  "Children": [
    {
      "$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 中的引用被正确保留。

演示 https://dotnetfiddle.net/j1Qhu6

更新 1

我的示例起作用而您在附加链接中发布的代码不起作用的原因是因为我的类包含默认构造函数，而您的没有。分析您的类，向它们添加默认构造函数，它不会破坏功能，并且反序列化将成功并正确初始化 Parent 属性。所以你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);
    }
}

您通过构造函数设置的 EntityName 属性将被正确反序列化，因为它是一个公共(public)属性。