使用Json.NET中的JsonConvert类检测反序列化的对象是否缺少字段 [英] Detect if deserialized object is missing a field with the JsonConvert class in Json.NET

问题描述

我正在尝试使用Json.NET反序列化一些JSON对象.但是我发现，当我反序列化不具有我要查找的属性的对象时，不会引发任何错误，但是访问属性时会返回默认值.重要的是，我能够检测到何时反序列化了错误类型的对象.示例代码:

I'm trying to deserialize some JSON objects using Json.NET. I've found however that when I deserialize an object that doesn't have the properties I'm looking for that no error is thrown up but a default value is returned for the properties when I access them. It's important that I'm able to detect when I've deserialized the wrong type of object. Example code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Newtonsoft.Json;

namespace Json_Fail_Test
{
    class Program
    {
        [JsonObject(MemberSerialization.OptOut)]
        private class MyJsonObjView
        {
            [JsonProperty("MyJsonInt")]
            public int MyJsonInt { get; set; }
        }

        const string correctData = @"
        {
            'MyJsonInt': 42
        }";

        const string wrongData = @"
        {
            'SomeOtherProperty': 'fbe8c20b'
        }";

        static void Main(string[] args)
        {
            var goodObj = JsonConvert.DeserializeObject<MyJsonObjView>(correctData);
            System.Console.Out.WriteLine(goodObj.MyJsonInt.ToString());

            var badObj = JsonConvert.DeserializeObject<MyJsonObjView>(wrongData);
            System.Console.Out.WriteLine(badObj.MyJsonInt.ToString());
        }
    }
}

该程序的输出为: 42 0

The output of this program is: 42 0

我宁愿引发异常而不是静默失败.缺少该方法是否可以检测序列化是否找不到参数?

I would prefer an exception be thrown to failing silently. Short of that is there a way to detect if the serialization failed to find a parameter?

我知道我可以使用Json对象解析数据，然后通过键值查找检查参数，但是我所使用的代码库使用上面的模式，并且如果可能的话，我希望保持一致.

I know I can parse the data with a Json object and then check for the parameter with a key value lookup but the codebase I'm in uses the pattern above and I'd like keep that consistent if it's possible.

推荐答案

Json.Net串行器具有MissingMemberHandling设置，您可以将其设置为Error. (默认值为Ignore.)这将导致序列化程序在反序列化过程中遇到目标类中没有对应属性的JSON属性时，在反序列化期间抛出JsonSerializationException.

The Json.Net serializer has a MissingMemberHandling setting which you can set to Error. (The default is Ignore.) This will cause the serializer to throw a JsonSerializationException during deserialization whenever it encounters a JSON property for which there is no corresponding property in the target class.

static void Main(string[] args)
{
    try
    {
        JsonSerializerSettings settings = new JsonSerializerSettings();
        settings.MissingMemberHandling = MissingMemberHandling.Error;

        var goodObj = JsonConvert.DeserializeObject<MyJsonObjView>(correctData, settings);
        System.Console.Out.WriteLine(goodObj.MyJsonInt.ToString());

        var badObj = JsonConvert.DeserializeObject<MyJsonObjView>(wrongData, settings);
        System.Console.Out.WriteLine(badObj.MyJsonInt.ToString());
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.GetType().Name + ": " + ex.Message);
    }
}

结果:

42
JsonSerializationException: Could not find member 'SomeOtherProperty' on object
of type 'MyJsonObjView'. Path 'SomeOtherProperty', line 3, position 33.

请参阅: MissingMemberHandling设置.

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