使用Json.NET用新的部分JSON数据修改现有对象

Question

考虑下面的示例程序

var calendar = new Calendar
{
    Id = 42,
    CoffeeProvider = "Espresso2000",
    Meetings = new[]
    {
        new Meeting
        {
            Location = "Room1",
            From = DateTimeOffset.Parse("2014-01-01T00:00:00Z"),
            To = DateTimeOffset.Parse("2014-01-01T01:00:00Z")
        },
        new Meeting
        {
            Location = "Room2",
            From = DateTimeOffset.Parse("2014-01-01T02:00:00Z"),
            To = DateTimeOffset.Parse("2014-01-01T03:00:00Z")
        },
    }
};

var patch = @"{
        'coffeeprovider': null,
        'meetings': [
            {
                'location': 'Room3',
                'from': '2014-01-01T04:00:00Z',
                'to': '2014-01-01T05:00:00Z'
            }
        ]
    }";

var patchedCalendar = Patch(calendar, patch);

该Patch()方法的结果应等于，calendar除非由更改patch。那意味着
Id将保持不变，CoffeeProvider设置为null并Meetings包含位于Room3中的单个项目。

1. 如何创建一种通用Patch()方法，该方法适用于Json.NET可反序列化的任何对象（不仅是示例Calendar对象）？

2. 如果（1）这不可行，将有哪些限制使其可行以及将如何实施？

Answer 1

您想要JsonSerializer.Populate()它的静态包装器方法JsonConvert.PopulateObject()：

将JSON值填充到目标对象上。

例如，这里正在更新您的Calendar类的实例：

public static class TestPopulate
{
    public static void Test()
    {
        var calendar = new Calendar
        {
            Id = 42,
            CoffeeProvider = "Espresso2000",
            Meetings = new[]
            {
                new Meeting
                {
                    Location = "Room1",
                    From = DateTimeOffset.Parse("2014-01-01T00:00:00Z"),
                    To = DateTimeOffset.Parse("2014-01-01T01:00:00Z")
                },
                new Meeting
                {
                    Location = "Room2",
                    From = DateTimeOffset.Parse("2014-01-01T02:00:00Z"),
                    To = DateTimeOffset.Parse("2014-01-01T03:00:00Z")
                },
            }
        };

        var patch = @"{
    'coffeeprovider': null,
    'meetings': [
        {
            'location': 'Room3',
            'from': '2014-01-01T04:00:00Z',
            'to': '2014-01-01T05:00:00Z'
        }
    ]
}";
        Patch(calendar, patch);

        Debug.WriteLine(JsonConvert.SerializeObject(calendar, Formatting.Indented));
    }

    public static void Patch<T>(T obj, string patch)
    {
        var serializer = new JsonSerializer();
        using (var reader = new StringReader(patch))
        {
            serializer.Populate(reader, obj);
        }
    }
}

产生的调试输出为：

{
  "id": 42,
  "coffeeprovider": null,
  "meetings": [
    {
      "location": "Room3",
      "from": "2014-01-01T04:00:00+00:00",
      "to": "2014-01-01T05:00:00+00:00"
    }
  ]
}

更新资料

如果要先复制，则可以执行以下操作：

    public static T CopyPatch<T>(T obj, string patch)
    {
        var serializer = new JsonSerializer();

        var json = JsonConvert.SerializeObject(obj);
        var copy = JsonConvert.DeserializeObject<T>(json);

        using (var reader = new StringReader(patch))
        {
            serializer.Populate(reader, copy);
        }

        return copy;
    }