c# - WebAPI JSON 序列化不序列化复合对象的任何子对象

Question

所以我需要将一个复合序列化为 JSON(使用 JSON.NET)，并希望来到这里解决这个问题会是一个快速的胜利。

我有一个非常基本的复合实现，我只是想用它来构建我的服务和数据结构，但 JSONSerializer 只序列化根节点。

代码:

namespace Data
{   
   public abstract class Element
   {
       protected string _name;
       public Element(string name)
       {
           _name = name;
       }
       public abstract void Add(Element element);


       public string Name { get { return _name; } }
   }

   public class ConcreteElement : Element
   {
      public ConcreteElement(string name) : base(name) { }
      public override void Add(Element element)
      {
         throw new InvalidOperationException("ConcreteElements may not contain Child nodes. Perhaps you intended to add this to a Composite");
      }
   }

    public class Composite: Element
    {
       public Composite(string name) : base(name) { Elements = new List<Element>(); }
       private List<Element> Elements { get; set; }
       public override void Add(Element element)
       {
           Elements.Add(element);
       }
    }
}

在我的 Controller 的 HttpGet 方法中，

Composite root = new Composite("Root");
Composite branch = new Composite("Branch");
branch.Add(new ConcreteElement("Leaf1"));
branch.Add(new ConcreteElement("Leaf2"));
root.Add(branch);
return JsonConvert.SerializeObject(root);

唯一被序列化的是

{"Name\":\"Root\"}"

谁能看出这不是序列化子元素的原因？我希望这是愚蠢的事情。

编辑1

我以前从未尝试过使用 WebAPI 将图形序列化为 JSON。我是否需要编写自定义 MediaTypeFormatter 来序列化它？

Edit2(添加所需的输出)

Leaf1 和 Leaf2 目前只是标记。一旦我可以将其序列化，它们本身就是复杂的对象。所以，此刻……

{
  "Name" : "Root"
  ,"Branch":  
           [
              {"Name":"Leaf1"}
             ,{"Name":"Leaf2"}
             ]
           ]
}

最终

{
   "Name" : "Root"
  ,"Branch1":
          [
            {"Name":"Leaf1", "Foo":"Bar"}
            {"Name":"Leaf2", "Foo":"Baz"} 
          ]
 ,"Branch2":
          [
            "Branch3":[
                        {"Name":"Leaf3", "Foo":"Quux"}
                      ]
          ]
}

Answer 1

子元素未被序列化，因为您的 Composite 中的元素列表是私有(private)的。 Json.Net 默认不会序列化私有(private)成员。如果您使用 [JsonProperty("Elements")] 标记列表，则子项将被序列化。

public class Composite: Element
{
   ...
   [JsonProperty("Elements")]
   private List<Element> Elements { get; set; }
   ...
}

如果您运行带有此更改的示例代码，您应该获得以下 JSON:

{
  "Elements": [
    {
      "Elements": [
        {
          "Name": "Leaf1"
        },
        {
          "Name": "Leaf2"
        }
      ],
      "Name": "Branch"
    }
  ],
  "Name": "Root"
}

编辑

好的，这是您的复合 Material 的示例转换器:

class CompositeConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return (objectType == typeof(Composite));
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        Composite composite = (Composite)value;

        // Need to use reflection here because Elements is private
        PropertyInfo prop = typeof(Composite).GetProperty("Elements", BindingFlags.NonPublic | BindingFlags.Instance);
        List<Element> children = (List<Element>)prop.GetValue(composite);

        JArray array = new JArray();
        foreach (Element e in children)
        {
            array.Add(JToken.FromObject(e, serializer));
        }

        JObject obj = new JObject();
        obj.Add(composite.Name, array);
        obj.WriteTo(writer);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

这是一个演示:

class Program
{
    static void Main(string[] args)
    {
        Composite root = new Composite("Root");
        Composite branch1 = new Composite("Branch1");
        branch1.Add(new ConcreteElement("Leaf1", "Bar"));
        branch1.Add(new ConcreteElement("Leaf2", "Baz"));
        root.Add(branch1);
        Composite branch2 = new Composite("Branch2");
        branch2.Add(new ConcreteElement("Leaf3", "Quux"));
        Composite branch3 = new Composite("Branch3");
        branch3.Add(new ConcreteElement("Leaf4", "Fizz"));
        branch2.Add(branch3);
        root.Add(branch2);
        string json = JsonConvert.SerializeObject(root, Formatting.Indented, new CompositeConverter());
        Console.WriteLine(json);
    }
}

public abstract class Element
{
    protected string _name;
    public Element(string name)
    {
        _name = name;
    }
    public abstract void Add(Element element);
    public string Name { get { return _name; } }
}

public class ConcreteElement : Element
{
    public ConcreteElement(string name, string foo) : base(name)
    {
        Foo = foo;
    }
    public string Foo { get; set; }
    public override void Add(Element element)
    {
        throw new InvalidOperationException("ConcreteElements may not contain Child nodes. Perhaps you intended to add this to a Composite");
    }
}

public class Composite : Element
{
    public Composite(string name) : base(name) { Elements = new List<Element>(); }
    private List<Element> Elements { get; set; }
    public override void Add(Element element)
    {
        Elements.Add(element);
    }
}

这是生成的 JSON 输出:

{
  "Root": [
    {
      "Branch1": [
        {
          "Foo": "Bar",
          "Name": "Leaf1"
        },
        {
          "Foo": "Baz",
          "Name": "Leaf2"
        }
      ]
    },
    {
      "Branch2": [
        {
          "Foo": "Quux",
          "Name": "Leaf3"
        },
        {
          "Branch3": [
            {
              "Foo": "Fizz",
              "Name": "Leaf4"
            }
          ]
        }
      ]
    }
  ]
}

我意识到这与您要求的 JSON 不完全相同，但它应该能让您朝着正确的方向前进。您在问题中指定的“所需”JSON 的一个问题是它不完全有效。命名属性只能在对象内部，不能直接在数组内部。在您的第二个示例中，您在“Branch2”的数组中直接有一个名为“Branch3”的属性。这行不通。因此，您需要将 Branch2 设为一个对象。但是如果你这样做，那么你的组合表示不一致:如果它只包含叶子，那么它是一个数组，否则它是一个对象。可以制作一个转换器来根据内容更改组合的表示(事实上我设法创建了这样一个野兽)，但这使得 JSON 更难以使用，最后我不认为你会想要使用它。如果您好奇，我在下面包含了这个备用转换器及其输出。

class CompositeConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return (objectType == typeof(Composite));
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        Composite composite = (Composite)value;

        // Need to use reflection here because Elements is private
        PropertyInfo prop = typeof(Composite).GetProperty("Elements", BindingFlags.NonPublic | BindingFlags.Instance);
        List<Element> children = (List<Element>)prop.GetValue(composite);

        // if all children are leaves, output as an array
        if (children.All(el => el.GetType() != typeof(Composite)))
        {
            JArray array = new JArray();
            foreach (Element e in children)
            {
                array.Add(JToken.FromObject(e, serializer));
            }
            array.WriteTo(writer);
        }
        else 
        {
            // otherwise use an object
            JObject obj = new JObject();
            if (composite.Name == "Root")
            {
                obj.Add("Name", composite.Name);
            }
            foreach (Element e in children)
            {
                obj.Add(e.Name, JToken.FromObject(e, serializer));
            }
            obj.WriteTo(writer);
        }
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

使用相同的数据输出:

{
  "Name": "Root",
  "Branch1": [
    {
      "Foo": "Bar",
      "Name": "Leaf1"
    },
    {
      "Foo": "Baz",
      "Name": "Leaf2"
    }
  ],
  "Branch2": {
    "Leaf3": {
      "Foo": "Quux",
      "Name": "Leaf3"
    },
    "Branch3": [
      {
        "Foo": "Fizz",
        "Name": "Leaf4"
      }
    ]
  }
}