Csharp System.Text.Json 将可空引用类型序列化反序列化为{}而不是null

发布于03月17日

try 将旧的ASP.NET Core项目从Newtonsoft.Json转换为System.Text.Json，但它更改了可为空的引用类型转换的行为.Json将可为空的引用类型序列化/反序列化为"{}"，而不是"NULL".我该怎么修好它？我想摆脱Newtonsoft.Json.

services.AddMvc().AddNewtonsoftJson();

以下是该列表public IList<IDictionary<string, object>> List { get; set; }的类型.实际值类型为DBNull.

System.Text.Json

{
    "data": {
        "list": [
            {
                "headers": [],
                "list": [
                    {
                        "id": "3faab29e-982d-ccb9-197b-08db24ef09e7",
                        "contractType": "Basis",
                        "tEvent": "Edit",
                        "Basis": 0.0000,
                        "fees": {},
                        "FlatPrice": {},
                        "theirContract": {}
                    },

Newtonsoft.Json

{
    "data": {
        "list": [
            {
                "headers": [],
                "list": [
                    {
                        "id": "3faab29e-982d-ccb9-197b-08db24ef09e7",
                        "contractType": "Basis",
                        "tEvent": "Edit",
                        "Basis": 0.0000,
                        "fees": null,
                        "FlatPrice": null,
                        "theirContract": null
                    },

推荐答案

在 compose 本报告时，有System.Text.Json does not have built-in support for DBNull个.

相反，您可以编写一个自定义JsonConverter来处理DBNull个值，方法是覆盖转换器的Write()方法以打印出JSON文本null:

public class DBNullJsonConverter : JsonConverter<DBNull> 
{ 
    public override bool CanConvert(Type typeToConvert) 
    { 
        return typeToConvert == typeof(DBNull); 
    } 
 
    public override DBNull Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) 
    { 
        throw new NotImplementedException(); 
    } 
 
    public override void Write(Utf8JsonWriter writer, DBNull value, JsonSerializerOptions options) 
    { 
        // write the JSON literal null
        writer.WriteNullValue(); 
    } 
}

然后，将此转换器传递给您的JsonSerializer中的JsonSerializerOptions:

var options = new JsonSerializerOptions();
options.Converters.Add(new DBNullJsonConverter());

// you should get null for fields of type DBNull here
var json = JsonSerializer.Serialize(someObject, options);