使用 System.Text.Json 时，有没有办法在对象上 return 自定义 JSON 结构？

Question

我正在编写不公开任何 public 属性的 class (AttributeBag)。在内部，我有一个通过 Get 和 Set 方法管理的对象（属性）列表。我希望能够在 AttributeBag class 上运行 JsonSerializer.Serialize() 并检索如下所示的 JSON 结构：

[
  {
    "Name": "x",
    "Value": "y"
  },
  {
    "Name": "x1",
    "Value": "y1"
  },
  {
    "Name": "x2",
    "Value": "y2"
  }
]

我的 Attribute 和 AttributeBag class看起来像这样：

public class Attribute
{
    public string Name { get; set; }
    public object Value { get; set; }
}

public class AttributeBag
{
    private readonly List<Attribute> attributes;

    public AttributeBag()
    {
        this.attributes = new List<Attribute>();
    }

    public AttributeBag Set(string name, object value)
    {
        var searchAttribute = this.attributes.Find(x => x.Name.Equals(name));

        if (searchAttribute != null)
        {
            searchAttribute.Value = value;
        }
        else
        {
            this.attributes.Add(new Attribute { Name = name, Value = value });
        }

        return this;
    }

    public Attribute Get(string name)
    {
        var searchAttribute = this.attributes.Find(x => x.Name.Equals(name));

        if (searchAttribute != null)
        {
            return searchAttribute;
        }
        else
        {
            throw new AttributeNameNotFoundException(name);
        }
    }

    public object GetValue(string name)
    {
        var searchAttribute = this.attributes.Find(x => x.Name.Equals(name));

        if (searchAttribute != null)
        {
            return searchAttribute.Value;
        }
        else
        {
            throw new AttributeNameNotFoundException(name);
        }
    }
}

我希望能够像这样简单地做一些事情：

var ab = new AttributeBag();
ab.Set("x", "y");
ab.Set("x1", "y1");
ab.Set("x2", "y2");
string jsonData = JsonSerializer.Serialize(ab);

我尝试查看文档，但不确定如何继续上述操作。我应该为此使用 Utf8JsonWriter 吗？看来，如果我使用 Utf8JsonWriter，我将需要一个实现 JSON 编写的函数，并使用 ab.Serialize() 调用它，而不需要直接使用 JsonSerializer。那是要走的路还是有办法使用 JsonSerializer.Serialize?

如有指点，将不胜感激！

Answer 1

如果您正在使用 Newtonsoft.Json，您可以像这样使用自定义 JsonConverter

using Newtonsoft.Json;
using System.Collections.Generic;

[JsonConverter(typeof(AttributeBagConverter))]
public class AttributeBag
{
    //private constructor to make it able to create instance from converter
    private AttributeBag(List<Attribute> attributes)
    {
        this.attributes = attributes;
    }

    public class AttributeBagConverter : JsonConverter<AttributeBag>
    {
        public override AttributeBag ReadJson(JsonReader reader, System.Type objectType, 
               AttributeBag existingValue, bool hasExistingValue, JsonSerializer serializer)
        {
            //deserialize as List<Attribute> and pass results to private constructor
            return new AttributeBag(serializer.Deserialize<List<Attribute>>(reader));
        }

        public override void WriteJson(JsonWriter writer, AttributeBag value, 
               JsonSerializer serializer)
        {
            //serialize List<Attribute> only
            serializer.Serialize(writer, value.attributes);
        }
    }
    /* rest of your code */
}

as you can see 它以您想要的方式序列化和反序列化您的对象

Answer 2

感谢 Sushant Yelpale 的提示和评论中的 link，我成功实现了如下自定义序列化。

我创建了一个新转换器class AttributeBagConverter:

class AttributeBagConverter : JsonConverter<AttributeBag>
{
    public override bool CanConvert(Type typeToConvert)
    {
        return true;
    }

    public override AttributeBag Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        throw new NotImplementedException();
    }

    public override void Write(Utf8JsonWriter writer, AttributeBag value, JsonSerializerOptions options)
    {
        writer.WriteStartArray();

        if (value.Count > 0)
        {           
            foreach (var item in value)
            {
                writer.WriteStartObject();

                writer.WritePropertyName("Name");
                writer.WriteStringValue(item.Name);

                writer.WritePropertyName("Value");
                if (double.TryParse(item.Value.ToString(), out double n))
                {
                    writer.WriteNumberValue(n);
                }
                else
                {
                    writer.WriteStringValue(item.Value.ToString());
                }

                writer.WriteEndObject();
            }           
        }

        writer.WriteEndArray();
        writer.Flush();
    }
}

然后我用 JsonConverter(typeof(AttributeBagConverter)):

装饰了我的 AttributeBag class

[JsonConverter(typeof(AttributeBagConverter))]
public class AttributeBag: IEnumerable<Attribute>
{
    private readonly List<Attribute> attributes;

    public int Count 
    { 
        get
        {
            return this.attributes.Count;
        }
    }

    public AttributeBag()
    {
        this.attributes = new List<Attribute>();
    }

    public AttributeBag Set(string name, object value)
    {
        var searchAttribute = this.attributes.Find(x => x.Name.Equals(name));

        if (searchAttribute != null)
        {
            searchAttribute.Value = value;
        }
        else
        {
            this.attributes.Add(new Attribute { Name = name, Value = value });
        }

        return this;
    }

    public Attribute Get(string name)
    {
        var searchAttribute = this.attributes.Find(x => x.Name.Equals(name));

        if (searchAttribute != null)
        {
            return searchAttribute;
        }
        else
        {
            throw new AttributeNameNotFoundException(name);
        }
    }

    public object GetValue(string name)
    {
        var searchAttribute = this.attributes.Find(x => x.Name.Equals(name));

        if (searchAttribute != null)
        {
            return searchAttribute.Value;
        }
        else
        {
            throw new AttributeNameNotFoundException(name);
        }
    }

    public IEnumerator<Attribute> GetEnumerator()
    {
        return this.attributes.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}

现在正在对象上调用 JsonSerializer.Serialize() returns 我正在寻找的正确 JSON 格式！

使用 System.Text.Json 时，有没有办法在对象上 return 自定义 JSON 结构？

Is there a way to return a custom JSON structure on an object when using System.Text.Json?

.net

c#

serialization

json

system.text.json