c# - 如何配置JSON.net解串器以跟踪缺少的属性？

范例类别:

public class ClassA
{
    public int Id { get; set; }
    public string SomeString { get; set; }
    public int? SomeInt { get; set; }
}

默认解串器:

var myObject = JsonConvert.DeserializeObject<ClassA>(str);

为两个不同的输入创建相同的对象

{"Id":5}

或者

{"Id":5,"SomeString":null,"SomeInt":null}

如何跟踪反序列化过程中缺少的属性并保持相同的行为？有没有一种方法可以重写某些JSON.net序列化器方法(例如DefaultContractResolver类方法)来实现这一点。例如:

List<string> missingProps;
var myObject = JsonConvert.DeserializeObject<ClassA>(str, settings, missingProps);

对于第一个输入列表，应包含缺少的属性的名称(“SomeString”，“SomeInt”)，对于第二个输入，列表应为空。反序列化的对象保持不变。

最佳答案

反序列化期间查找空/未定义 token 的另一种方法是编写自定义JsonConverter，这是一个自定义转换器的示例，该转换器可以报告省略的 token (例如"{ 'Id':5 }")和空 token (例如{"Id":5,"SomeString":null,"SomeInt":null})

public class NullReportConverter : JsonConverter
{
    private readonly List<PropertyInfo> _nullproperties=new List<PropertyInfo>();
    public bool ReportDefinedNullTokens { get; set; }

    public IEnumerable<PropertyInfo> NullProperties
    {
        get { return _nullproperties; }
    }

    public void Clear()
    {
        _nullproperties.Clear();
    }

    public override bool CanConvert(Type objectType)
    {
        return true;
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        existingValue = existingValue ?? Activator.CreateInstance(objectType, true);

        var jObject = JObject.Load(reader);
        var properties =
            objectType.GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);

        foreach (var property in properties)
        {
            var jToken = jObject[property.Name];
            if (jToken == null)
            {
                _nullproperties.Add(property);
                continue;
            }

            var value = jToken.ToObject(property.PropertyType);
            if(ReportDefinedNullTokens && value ==null)
                _nullproperties.Add(property);

            property.SetValue(existingValue, value, null);
        }

        return existingValue;
    }

    //NOTE: we can omit writer part if we only want to use the converter for deserializing
    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var objectType = value.GetType();
        var properties =
            objectType.GetProperties(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);

        writer.WriteStartObject();
        foreach (var property in properties)
        {
            var propertyValue = property.GetValue(value, null);
            writer.WritePropertyName(property.Name);
            serializer.Serialize(writer, propertyValue);
        }

        writer.WriteEndObject();
    }
}

注意:如果我们不需要使用Writer部分来序列化对象，则可以省略它。

用法示例:

class Foo
{
    public int Id { get; set; }
    public string SomeString { get; set; }
    public int? SomeInt { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        var nullConverter=new NullReportConverter();

        Console.WriteLine("Pass 1");
        var obj0 = JsonConvert.DeserializeObject<Foo>("{\"Id\":5, \"Id\":5}", nullConverter);
        foreach(var p in nullConverter.NullProperties)
            Console.WriteLine(p);

        nullConverter.Clear();

        Console.WriteLine("Pass2");
        var obj1 = JsonConvert.DeserializeObject<Foo>("{\"Id\":5,\"SomeString\":null,\"SomeInt\":null}" , nullConverter);
        foreach (var p in nullConverter.NullProperties)
            Console.WriteLine(p);

        nullConverter.Clear();

        nullConverter.ReportDefinedNullTokens = true;
        Console.WriteLine("Pass3");
        var obj2 = JsonConvert.DeserializeObject<Foo>("{\"Id\":5,\"SomeString\":null,\"SomeInt\":null}", nullConverter);
        foreach (var p in nullConverter.NullProperties)
            Console.WriteLine(p);
    }
}

关于c# - 如何配置JSON.net解串器以跟踪缺少的属性？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/30300740/