使用JsonSerializer选择性地读取部分JSON数据并填充ac#object

Question

我连接到第三方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一些信息.

基本上,我只需要"值"中的数组.从该数组中,我只需要"Id","Title"和"Status"属性.

我想将这些属性放入名为Project的ac#类中.这是我的班级:

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并执行转换:

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null对象.但是在调试器中,我可以看到它正在从Web服务中提取所有JSON数据.

如何从JSON获得我需要的东西,构建我的c#对象,并忽略所有其余的东西？

Answer 1

如果你可以使用Json.NET(Newtonsoft json),你可以Linq-to-Json像这样使用[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JObject将此类型反序列化[2]

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

两者都很好,但哪一个更好？

第二种方法是指更少的代码(特别是,如果有许多属性Project类,你必须写的多行代码的每个属性在代码映射[1]).

但第一种方法的表现要好很多倍!对于给定的json数据,代码[1]大约在1毫秒内运行,而代码[2]需要超过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式来做到这一点[3]

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

你猜怎么着!这段代码[3]花费了近一半的时间[1].因此,从各方面来看,这必须是最好的方法!