如何使用 Newtonsoft 反序列化复杂的 JSON？（NASA API Neo Feed）

Question

我是论坛新手，遇到了问题。

我正在尝试使用 Newtonsoft 反序列化 NASA API 的 Neo Feed，但出现此错误

Newtonsoft.Json.JsonSerializationException: Cannot deserialize the current JSON object (e.g. {"name":"value"}) into type 'System.Collections.Generic.IEnumerable1[NasaApi.Models.Near_Earth_Objects]' because the type requires a JSON array (e.g. [1,2,3]) to deserialize correctly. To fix this error either change the JSON to a JSON array (e.g. [1,2,3]) or change the deserialized type so that it is a normal .NET type (e.g. not a primitive type like integer, not a collection type like an array or List<T>) that can be deserialized from a JSON object. JsonObjectAttribute can also be added to the type to force it to deserialize from a JSON object. Path 'links', line 1, position 9. at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue) at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue) at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent) at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType) at Newtonsoft.Json.JsonSerializer.Deserialize(JsonReader reader, Type objectType) at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings) at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonSerializerSettings settings) at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value) at NasaApi.Services.NearEarthObjectService.GetAllNeos() in C:\Users\santanitaxx1050\Desktop\NasaApi\NasaApi\Services\NearEarthObjectService.cs:line 18 at lambda_method5(Closure , Object ) at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask1 actionResultValueTask) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeNextActionFilterAsync>g__Awaited|10_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeInnerFilterAsync>g__Awaited|13_0(ControllerActionInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|20_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope) at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger) at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context) at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext) at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider) at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

HEADERS

Accept: / Host: localhost:7008 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/100.0.4896.79 Safari/537.36 :method: GET Accept-Encoding: gzip, deflate, br Accept-Language: es-ES,es;q=0.9 Cache-Control: no-cache postman-token: ec30b624-b8b6-770d-57ce-4b6dcda1ffc2 sec-gpc: 1 sec-fetch-site: none sec-fetch-mode: cors sec-fetch-dest: empty

我试过了

public async Task<IEnumerable<Near_Earth_Objects>> GetAllNeos()
{
    var json = await _httpClient.GetStringAsync($"feed?start_date=2021-11-07&end_date=2021-11-10&api_key=Na1sKwJGK1HVeOF4Yx8aLNp4u8ygT5GSSMF26HQ2");
    return JsonConvert.DeserializeObject<IEnumerable<Near_Earth_Objects>>(json);
}

有了这个JSON

{
"links": {
    "next": "http://www.neowsapp.com/rest/v1/feed?start_date=2021-12-12&end_date=2021-12-15&detailed=false&api_key=Na1sKwJGK1HVeOF4Yx8aLNp4u8ygT5GSSMF26HQ2",
    "prev": "http://www.neowsapp.com/rest/v1/feed?start_date=2021-12-06&end_date=2021-12-09&detailed=false&api_key=Na1sKwJGK1HVeOF4Yx8aLNp4u8ygT5GSSMF26HQ2",
    "self": "http://www.neowsapp.com/rest/v1/feed?start_date=2021-12-09&end_date=2021-12-12&detailed=false&api_key=Na1sKwJGK1HVeOF4Yx8aLNp4u8ygT5GSSMF26HQ2"
},
"element_count": 76,
"near_earth_objects": {
    "2021-12-12": [
        {
            "links": {
                "self": "http://www.neowsapp.com/rest/v1/neo/2004341?api_key=Na1sKwJGK1HVeOF4Yx8aLNp4u8ygT5GSSMF26HQ2"
            },
            "id": "2004341",
            "neo_reference_id": "2004341",
            "name": "4341 Poseidon (1987 KF)",
            "nasa_jpl_url": "http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2004341",
            "absolute_magnitude_h": 16.05,
            "estimated_diameter": {
                "kilometers": {
                    "estimated_diameter_min": 1.6389095149,
                    "estimated_diameter_max": 3.6647130844
                },
                "meters": {
                    "estimated_diameter_min": 1638.9095149478,
                    "estimated_diameter_max": 3664.7130843945
                },
                "miles": {
                    "estimated_diameter_min": 1.0183708442,
                    "estimated_diameter_max": 2.277146434
                },
                "feet": {
                    "estimated_diameter_min": 5376.9998930214,
                    "estimated_diameter_max": 12023.337275805
                }
            },
            "is_potentially_hazardous_asteroid": false,
            "close_approach_data": [
                {
                    "close_approach_date": "2021-12-12",
                    "close_approach_date_full": "2021-Dec-12 13:35",
                    "epoch_date_close_approach": 1639316100000,
                    "relative_velocity": {
                        "kilometers_per_second": "17.8282207618",
                        "kilometers_per_hour": "64181.5947426121",
                        "miles_per_hour": "39879.9470221525"
                    },
                    "miss_distance": {
                        "astronomical": "0.3316696597",
                        "lunar": "129.0194976233",
                        "kilometers": "49617074.634744839",
                        "miles": "30830620.5431592182"
                    },
                    "orbiting_body": "Earth"
                }
            ],
            "is_sentry_object": false
        },

制作这个模型

public class Near_Earth_Objects
{
    [JsonProperty("id")]
    public int Id { get; set; }
    [JsonProperty("name")]
    public string Nombre { get; set; }
    
    [JsonProperty("estimated_diameter:kilometers:estimated_diameter_min")]
    public double DiametroMin { get; set; }
    
    [JsonProperty("estimated_diameter:kilometers:estimated_diameter_max")]
    public double DiametroMax { get; set; }
    
    [JsonProperty("close_approach_data:relative_velocity:kilometers_per_hour")]
    public double Velocidad { get; set; }
    
    [JsonProperty("close_approach_data: close_approach_date")]
    public DateTime Fecha { get; set; }
    
    [JsonProperty("close_approach_date: orbiting_body")]
    public string Planeta { get; set; }
}

我的反序列化代码是这样的

public async Task<IEnumerable<Near_Earth_Objects>> GetAllNeos()
{
    var json = await _httpClient.GetStringAsync($"feed?start_date=2021-11-07&end_date=2021-11-10&api_key=Na1sKwJGK1HVeOF4Yx8aLNp4u8ygT5GSSMF26HQ2");
    return JsonConvert.DeserializeObject<IEnumerable<Near_Earth_Objects>>(json);
}

要查看 JSON 响应，请在 POSTMAN 上尝试此操作：

https://api.nasa.gov/neo/rest/v1/feed?start_date=2021-11-07&end_date=2021-11-10&api_key=Na1sKwJGK1HVeOF4Yx8aLNp4u8ygT5GSSMF26HQ2

感谢大家！！抱歉我的英语不好，我来自西班牙:)

Answer 1

这确实是一个复杂的架构，因此自动生成 DTO 并不容易。因此，您不应该 为属性使用自定义名称。这使得发现问题变得更加困难。

near_earth_objects部分实际上是一本日常观察的字典。与其创建 near_earth_objects class，不如使用 Dictionary<string,Observation[]>.
links 包含指向提要中当前页面、下一页和上一页的链接。这意味着您实际上可以创建一个 class 并在根级别和日常观察中重复使用它

您可以使用 DTO 生成器工具开始，但结果需要修改。工具将无法识别 near_earth_objects 是一个字典，并且很容易最终为每个条目创建新类型。

DTO

使用您的 JSON 示例，我使用 Visual Studio 的 Paste as Json 创建了初始 classes，然后修改它们以使其正常工作。

public class Rootobject
{
    public PageLinks links { get; set; }
    public int element_count { get; set; }
    public Dictionary<string,Observation[]> near_earth_objects { get; set; }
}

public class PageLinks
{
    public string? next { get; set; }
    public string? prev { get; set; }
    public string self { get; set; }
}

Observation class 使用相同的 PageLinks class links 属性:

public class Observation
{
    public PageLinks links { get; set; }
    public string id { get; set; }
    public string neo_reference_id { get; set; }
    public string name { get; set; }
    public string nasa_jpl_url { get; set; }
    public float absolute_magnitude_h { get; set; }
    public Estimated_Diameter estimated_diameter { get; set; }
    public bool is_potentially_hazardous_asteroid { get; set; }
    public Close_Approach_Data[] close_approach_data { get; set; }
    public bool is_sentry_object { get; set; }
}

其余 classes 不需要修改：

public class Estimated_Diameter
{
    public Kilometers kilometers { get; set; }
    public Meters meters { get; set; }
    public Miles miles { get; set; }
    public Feet feet { get; set; }
}

public class Kilometers
{
    public float estimated_diameter_min { get; set; }
    public float estimated_diameter_max { get; set; }
}

public class Meters
{
    public float estimated_diameter_min { get; set; }
    public float estimated_diameter_max { get; set; }
}

public class Miles
{
    public float estimated_diameter_min { get; set; }
    public float estimated_diameter_max { get; set; }
}

public class Feet
{
    public float estimated_diameter_min { get; set; }
    public float estimated_diameter_max { get; set; }
}

public class Close_Approach_Data
{
    public string close_approach_date { get; set; }
    public string close_approach_date_full { get; set; }
    public long epoch_date_close_approach { get; set; }
    public Relative_Velocity relative_velocity { get; set; }
    public Miss_Distance miss_distance { get; set; }
    public string orbiting_body { get; set; }
}

public class Relative_Velocity
{
    public string kilometers_per_second { get; set; }
    public string kilometers_per_hour { get; set; }
    public string miles_per_hour { get; set; }
}

public class Miss_Distance
{
    public string astronomical { get; set; }
    public string lunar { get; set; }
    public string kilometers { get; set; }
    public string miles { get; set; }
}

测试模型

使用此模型，以下测试通过：

[Fact]
public async Task GetFeed()
{
    var client = new HttpClient();
    var url = "http://www.neowsapp.com/rest/v1/feed?start_date=2021-12-09&end_date=2021-12-12&detailed=false&api_key=Na1sKwJGK1HVeOF4Yx8aLNp4u8ygT5GSSMF26HQ2";
    var feed = await client.GetFromJsonAsync<Rootobject>(url);

    Assert.Equal(76,feed.element_count);
    var allObservations = feed.near_earth_objects
        .SelectMany(p => p.Value)
        .ToList();
    Assert.Equal(76,allObservations.Count);
}

Answer 2

错误是因为下面一行：

JsonConvert.DeserializeObject<IEnumerable<Near_Earth_Objects>>(json);

您收到此错误是因为 API returns 一个 单个对象 但您想将其反序列化为 IEnumerable。

为了解决，将其更改为：

JsonConvert.DeserializeObject<ApiResultDataModel>(json);

和ApiResultDataModel如下：

public class ApiResultDataModel
{
   public Links links { get; set; }
   public int element_count { get; set; }
   public Dictionary<string, Near_Earth_Objects[]> near_earth_objects { get; set; }
}

public class Links
{
    public string next { get; set; }
    public string prev { get; set; }
    public string self { get; set; }
}

通过执行此操作，您的数据将成功反序列化：

我希望这个答案对你有帮助。祝你好运。

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