c# - 使用 System.Text.Json.Serialization 将动态对象转换为 json 时引发异常

Question

我想将动态对象转换为 json 字符串。当我过去使用 Newtonsoft.Json 时，它运行良好。当我将 .net 核心升级到 3.0 并改用 System.Text.Json 时，情况很糟糕。

见代码：

using System;
using System.Collections.Generic;
using System.Dynamic;
namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            dynamic product = new ExpandoObject();
            product.ProductName = "Elbow Grease";
            product.Enabled = true;
            product.Price = 4.90m;
            product.StockCount = 9000;
            product.StockValue = 44100;
            product.Tags = new string[] { "Real", "OnSale" };

            // Will output: { "ProductName":"Elbow Grease","Enabled":true,"Price":4.90,
            // "StockCount":9000,"StockValue":44100,"Tags":["Real","OnSale"]}
            var json1 = Newtonsoft.Json.JsonConvert.SerializeObject(product);
            Console.WriteLine(json1);

            // Both will throw exception: System.InvalidCastException:“Unable to
            // cast object of type '<GetExpandoEnumerator>d__51' to type
            // 'System.Collections.IDictionaryEnumerator'.”
            var json2 = System.Text.Json.JsonSerializer.Serialize(product);
            Console.WriteLine(json2);
            var json3 = System.Text.Json.JsonSerializer.Serialize<IDictionary<string, object>>(product as IDictionary<string, object>);
            Console.WriteLine(json3);

            Console.ReadKey();
        }
    }
}

如果我想坚持使用 System.Text.Json 来转换动态对象，因为我听说它比其他 json 转换更快，我该怎么办？

Answer 1

这被记录为对 ExpandoObject #38007 的 JsonSerializer 支持，截至 2019 年 10 月 21 日仍然开放。

您可以改用匿名类型。

var product = new {
            ProductName = "Elbow Grease",
            Enabled = true,
            Price = 4.90m,
            StockCount = 9000,
            StockValue = 44100,
            Tags = new string[] { "Real", "OnSale" }
        };


var json1 = Newtonsoft.Json.JsonConvert.SerializeObject(product);
Console.WriteLine(json1);

var json2 = System.Text.Json.JsonSerializer.Serialize(product);
Console.WriteLine(json2);

{"ProductName":"Elbow Grease","Enabled":true,"Price":4.90,"StockCount":9000,"StockValue":44100,"Tags":["Real","OnSale"]}
{"ProductName":"Elbow Grease","Enabled":true,"Price":4.90,"StockCount":9000,"StockValue":44100,"Tags":["Real","OnSale"]}