无需Newtonsoft [JsonExtensionData]特性实现模型扩展数据可行吗？

Hey there! Great question—yes, you absolutely can get the result you want without relying on Newtonsoft's [JsonExtensionData] attribute. The solution is to build a custom JsonConverter that manually handles any extra properties in your JSON, just like the attribute does. Let me walk you through a practical example.

核心思路 #

We'll create a converter that:

• During deserialization: Maps known model properties first, then stores any unrecognized JSON keys/values into a dedicated collection (like a dictionary) in your model.
• During serialization: Merges that collection of extra properties back into the final JSON output.

Step 1: Define Your Model #

First, add a collection to your model to hold the extra properties (this replaces the [JsonExtensionData] attribute's storage):

public class YourModel
{
    // Your existing known properties
    public string ExpectedProperty1 { get; set; }
    public int ExpectedProperty2 { get; set; }

    // Collection to store extra JSON properties
    public Dictionary<string, object> ExtraProperties { get; set; } = new Dictionary<string, object>();
}

Step 2: Implement the Custom JsonConverter #

This converter will handle the heavy lifting of moving extra properties between JSON and your model:

using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System.Reflection;

public class YourModelConverter : JsonConverter<YourModel>
{
    public override YourModel ReadJson(JsonReader reader, Type objectType, YourModel existingValue, bool hasExistingValue, JsonSerializer serializer)
    {
        var model = existingValue ?? new YourModel();
        var jsonObject = JObject.Load(reader);

        // First, populate the known model properties
        serializer.Populate(jsonObject.CreateReader(), model);

        // Then, add any unrecognized properties to ExtraProperties
        foreach (var jsonProperty in jsonObject.Properties())
        {
            var modelProperty = model.GetType().GetProperty(
                jsonProperty.Name, 
                BindingFlags.Public | BindingFlags.Instance
            );
            
            if (modelProperty == null)
            {
                model.ExtraProperties[jsonProperty.Name] = jsonProperty.Value.ToObject<object>(serializer);
            }
        }

        return model;
    }

    public override void WriteJson(JsonWriter writer, YourModel value, JsonSerializer serializer)
    {
        // Convert the model to a JObject (includes known properties)
        var jsonObject = JObject.FromObject(value, serializer);

        // Add all extra properties from the dictionary to the JObject
        foreach (var extraProp in value.ExtraProperties)
        {
            jsonObject.Add(extraProp.Key, JToken.FromObject(extraProp.Value, serializer));
        }

        // Write the final combined JSON
        jsonObject.WriteTo(writer);
    }
}

Step 3: Use the Converter #

You have two ways to enable this converter:

Option 1: Attribute the Model #

Mark your model with the converter so it's used automatically:

[JsonConverter(typeof(YourModelConverter))]
public class YourModel
{
    // ... your properties ...
}

Option 2: Specify During Serialization/Deserialization #

Add the converter to your JsonSerializerSettings when you call the Newtonsoft methods:

var settings = new JsonSerializerSettings();
settings.Converters.Add(new YourModelConverter());

// Deserialize JSON to your model
var model = JsonConvert.DeserializeObject<YourModel>(yourInputJson, settings);

// Serialize the model back to JSON (includes extra properties)
var outputJson = JsonConvert.SerializeObject(model, settings);

Customization Tips #

• If you know all extra properties will be a specific type (e.g., strings), replace Dictionary<string, object> with Dictionary<string, string> and adjust the ToObject call accordingly.
• If you don't want a public ExtraProperties property, you can make it private and adjust the converter to access it via reflection (though public is simpler for most cases).

内容的提问来源于stack exchange，提问作者LEspera