System.Text.Json：获取自定义转换器中的属性名称

Question

使用 JsonSerialize.DeserializeAsync 和自定义转换器反序列化，例如

public class MyStringJsonConverter : JsonConverter<string>
{
    public override string Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        return reader.GetString();
    }

    public override void Write(Utf8JsonWriter writer, string value, JsonSerializerOptions options)
    {
        throw new NotImplementedException();
    }
}

在这里我会得到 all string 属性，这还可以，但有什么方法可以检查给定的属性名称值，例如像这样，在哪里只处理 Body 属性:

class MyMailContent 
{
    public string Name { get; set; }
    public string Subject { get; set; }
    public string Body { get; set; }
}

public class MyStringJsonConverter : JsonConverter<string>
{
    public override string Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.PropertyName.Equals("Body"))
        {
            var s = reader.GetString();
            //do some process with the string value
            return s;
        }

        return reader.GetString();
    }
}

或者是否有其他方法可以挑出给定的属性？

请注意，我正在寻找使用 System.Text.Json 的解决方案。

Answer 1

System.Text.Json 不会使父属性成为名称，或者更一般地说，path to the current value, available inside JsonConverter<T>.Read(). This information is tracked internally -- it's in ReadStack.JsonPath() -- but ReadStack 是内部的，从未传递给应用程序代码。

但是，如 Registration sample - [JsonConverter] on a property, you can apply your MyStringJsonConverter directly to public string Body { get; set; } by using JsonConverterAttribute 中所述：

class MyMailContent 
{
    public string Name { get; set; }
    public string Subject { get; set; }
    [JsonConverter(typeof(MyStringJsonConverter))]
    public string Body { get; set; }
}

通过这样做，MyStringJsonConverter.Read() 和 .Write() 将仅针对 MyMailContent.Body 触发。即使你在 JsonSerializerOptions.Converters, the converter applied to the property will take precedence 中有一些整体 JsonConverter<string>:

During serialization or deserialization, a converter is chosen for each JSON element in the following order, listed from highest priority to lowest:

[JsonConverter] applied to a property.

A converter added to the Converters collection.

[JsonConverter] applied to a custom value type or POCO.

（请注意，这与 Newtonsoft 有部分不同，其中应用于类型的转换器会取代设置中的转换器。）

Answer 2

感谢 Jimi for the ，在他的祝福下，我 post 使用他建议的解决方案进行了 wiki 回答，任何有更多贡献的人，请随时这样做。

在大多数情况下，公认的答案是好的，但如果仍然需要通过属性名称处理一个或多个特定属性，这里有一种方法可以做到这一点。

public class MyMailContent
{
    public string Name { get; set; }
    public string Subject { get; set; }
    public string Body { get; set; }
}

public class MyMailContentJsonConverter : JsonConverter<MyMailContent>
{
    public override MyMailContent Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.TokenType != JsonTokenType.StartObject)
        {
            throw new JsonException();
        }

        var mailContent = new MyMailContent();

        while (reader.Read())
        {
            if (reader.TokenType == JsonTokenType.EndObject)
            {
                return mailContent;
            }

            if (reader.TokenType == JsonTokenType.PropertyName)
            {
                var propertyName = reader.GetString();

                reader.Read();

                switch (propertyName)
                {
                    case "Name":
                        mailContent.Name = reader.GetString();
                        break;

                    case "Subject":
                        mailContent.Subject = reader.GetString();
                        break;

                    case "Body":
                        string body = reader.GetString();
                        //do some process on body here
                        mailContent.Body = body;
                        break;
                }
            }
        }

        throw new JsonException();
    }

    public override void Write(Utf8JsonWriter writer, MyMailContent mailcontent, JsonSerializerOptions options)
    {
        throw new NotImplementedException();
    }
}

private static JsonSerializerOptions _jsonDeserializeOptions = new()
{
    ReadCommentHandling = JsonCommentHandling.Skip,
    AllowTrailingCommas = true,
    Converters =
    {
        new MyMailContentJsonConverter()
    }
};

然后像这样使用它

var jsonstring = JsonSerializer.Serialize(new MyMailContent
{
    Name = "some name",
    Subject = "some subject",
    Body = "some body"
});

var MailContent = JsonSerializer.Deserialize<MyMailContent>(jsonstring, _jsonDeserializeOptions);

System.Text.Json：获取自定义转换器中的属性名称

System.Text.Json: Get the property name in a custom converter

c#

json-deserialization

system.text.json

asp.net-core-5.0