使用 JsonSerializer 选择性地读取部分 JSON 数据并填充 c# 对象

Question

我连接到第 3 方 Web 服务，该服务返回一个复杂的 JSON 对象，该对象仅包含我实际需要的少量信息。

基本上，我只需要“值”中的数组。从那个数组中，我只需要“Id”、“Title”和“Status”属性。

我想将这些属性放入一个名为 Project 的 c# 类中。这是我的课：

public class Project
{
    public String Id { get; set; }
    public String Title { get; set; }
    public String Status { get; set; }
}

我正在尝试使用此代码来读取 JSON 并进行转换：

using (WebResponse response = request.GetResponse())
{
    using (StreamReader reader = new StreamReader(response.GetResponseStream()))
    {
        var serializer = new JsonSerializer();
        var jsonTextReader = new JsonTextReader(reader);
        returnValue = serializer.Deserialize<Project>(jsonTextReader);
    }
}

示例 JSON：

{
    "odata.metadata":"http://school.edu/Api/1/$metadata#Projects",
    "odata.count":"3",
    "value":[
        {
            "odata.id":"http://school.edu/Api/1/Projects('123')",
            "RelatedProjects@odata.navigationLinkUrl":"http://school.edu/Api/1/Projects('123')/RelatedProjects",
            "Tags@odata.navigationLinkUrl":"http://school.edu/Api/1/Projects('123')/Tags",
            "TimedEvents@odata.navigationLinkUrl":"http://school.edu/Api/1/Projects('123')/Categories",
            "ep@odata.navigationLinkUrl":"http://school.edu/Api/1/Projects('123')/ep",
            "#CreateLike":{
                    "target":"http://school.edu/Api/1/Projects('123')/CreateLike"
                  },
            "#CreateShortcut":{
                        "target":"http://school.edu/Api/1/Projects('123')/CreateShortcut"
                      },
            "#Play":{
                        "target":"http://school.edu/Play/123"
                      },
            "#SendInvitation":{
                        "target":"http://school.edu/Api/1/Projects('123')/SendInvitation"
                      },
            "#CopyProject":{
                        "target":"http://school.edu/Api/1/Projects('123')/CopyProject"
                      },
            "#AddVideoPodcast":{
                        "target":"http://school.edu/Api/1/Projects('123')/AddVideoPodcast"
                      },
            "#AddEP":{
                        "target":"http://school.edu/Api/1/Projects('123')/AddEP"
                      },
            "Id":"123",
            "Title":"Test Title 1",
            "Status":"Viewable"
        },
        {
            "odata.id":"http://school.edu/Api/1/Projects('456')",
            "RelatedProjects@odata.navigationLinkUrl":"http://school.edu/Api/1/Projects('456')/RelatedProjects",
            "Tags@odata.navigationLinkUrl":"http://school.edu/Api/1/Projects('456')/Tags",
            "TimedEvents@odata.navigationLinkUrl":"http://school.edu/Api/1/Projects('456')/Categories",
            "ep@odata.navigationLinkUrl":"http://school.edu/Api/1/Projects('456')/ep",
            "#CreateLike":{
                    "target":"http://school.edu/Api/1/Projects('456')/CreateLike"
                  },
            "#CreateShortcut":{
                        "target":"http://school.edu/Api/1/Projects('456')/CreateShortcut"
                      },
            "#Play":{
                        "target":"http://school.edu/Play/456"
                      },
            "#SendInvitation":{
                        "target":"http://school.edu/Api/1/Projects('456')/SendInvitation"
                      },
            "#CopyProject":{
                        "target":"http://school.edu/Api/1/Projects('456')/CopyProject"
                      },
            "#AddVideoPodcast":{
                        "target":"http://school.edu/Api/1/Projects('456')/AddVideoPodcast"
                      },
            "#AddEP":{
                        "target":"http://school.edu/Api/1/Projects('456')/AddEP"
                      },
            "Id":"456",
            "Title":"Test Title 2",
            "Status":"Viewable"
        },
        {
            "odata.id":"http://school.edu/Api/1/Projects('789')",
            "RelatedProjects@odata.navigationLinkUrl":"http://school.edu/Api/1/Projects('789')/RelatedProjects",
            "Tags@odata.navigationLinkUrl":"http://school.edu/Api/1/Projects('789')/Tags",
            "TimedEvents@odata.navigationLinkUrl":"http://school.edu/Api/1/Projects('789')/Categories",
            "ep@odata.navigationLinkUrl":"http://school.edu/Api/1/Projects('789')/ep",
            "#CreateLike":{
                    "target":"http://school.edu/Api/1/Projects('789')/CreateLike"
                  },
            "#CreateShortcut":{
                        "target":"http://school.edu/Api/1/Projects('789')/CreateShortcut"
                      },
            "#Play":{
                        "target":"http://school.edu/Play/789"
                      },
            "#SendInvitation":{
                        "target":"http://school.edu/Api/1/Projects('789')/SendInvitation"
                      },
            "#CopyProject":{
                        "target":"http://school.edu/Api/1/Projects('789')/CopyProject"
                      },
            "#AddVideoPodcast":{
                        "target":"http://school.edu/Api/1/Projects('789')/AddVideoPodcast"
                      },
            "#AddEP":{
                        "target":"http://school.edu/Api/1/Projects('789')/AddEP"
                      },
            "Id":"789",
            "Title":"Test Title 3",
            "Status":"Viewable"
        }
  ],
  "odata.nextLink":"http://school.edu/Api/1/Folders('xyz')/Projects?$skip=10&$top=10"
}

我只是得到一个空对象。但在调试器中，我可以看到它正在从 web 服务中提取所有 JSON 数据。

如何从 JSON 中获取我需要的内容，构建我的 c# 对象，而忽略其他所有内容？

Answer 1

如果你可以使用Json.NET（Newtonsoft json），你可以像这样使用Linq-to-Json [1]

//using Newtonsoft.Json.Linq;
var jsonString = File.ReadAllText(@"C:YourDirectory\file.json"); //source
var projects = new List<Project>(); //Your result

JObject data = JObject.Parse(jsonString);
foreach (var value in data["value"])
{
    projects.Add(new Project
    {
        Id = value["Id"].ToString(),
        Status = value["Status"].ToString(),
        Title = value["Title"].ToString()
    });
}

或者，您也可以像这样反序列化JObject [2]

var jsonReader = data["value"].CreateReader();
projects = new JsonSerializer().Deserialize<List<Project>>(jsonReader);

两者都可以，但哪个更好？

第二种方法意味着更少的代码（特别是，如果Project 类中有许多属性，则必须编写多行代码来映射代码 [1] 中的每个属性）。

但是第一种方法的性能要好很多倍！对于给定的 json 数据，代码 [1] 的运行时间大约为 1 毫秒，而代码 [2] 的运行时间超过 100 毫秒！

---

更新

在 James Newton-King（编写 Json.NET :) 的输入之后，还有另一种更优雅的方法 [3]

projects = data["value"].ToObject<List<Project>>();

你猜怎么着！这段代码 [3] 花费了接近 [1] 的时间几乎 一半。所以，从各个角度来看，这一定是最好的方法！