WebAPI JSON序列化不序列化复合对象的任何子项

Question

所以我需要将一个组合序列化为JSON(使用JSON.NET),并且希望能够快速获得这个问题.

我有一个非常基本的复合实现,我只是试图用来支撑我的服务和数据结构,但JSONSerializer只是序列化根节点.

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\"}"

任何人都可以看到这不是序列化子元素的原因吗？我希望这是一个愚蠢的事情.

EDIT1

我以前从未尝试使用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.一旦我可以将它序列化,它们本身就是复杂的对象.所以,目前......

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

并最终

{
   "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Composite中的元素列表是私有的.默认情况下,Json.Net不会序列化私有成员.如果您使用标记列表,[JsonProperty("Elements")]那么将序列化子项.

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

如果您使用此更改运行示例代码,则应获取以下JSON:

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

编辑

好的,这是您的复合材料的示例转换器:

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);
    }
}

以下是生成的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,而不能直接在数组内.在第二个示例中,您在数组中直接为"Branch2"命名了一个名为"Branch3"的属性.这不行.因此,您需要将Branch2替换为对象.但是如果你这样做,那么你的复合表示不一致:如果它只包含叶子,那么它就是一个数组,否则就是一个对象.有可能使转换器根据内容更改组合的表示(事实上我设法创建了这样的野兽),但这使得JSON更难以消耗,最后我不认为你我会想用它.如果你很好奇,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"
      }
    ]
  }
}