.NET Core 表单提交在 Microsoft.Azure.Documents.Document.get_AttachmentsLink() 处引发 NullReferenceException

Question

提交表单时，我收到以下错误：

异常详情

System.NullReferenceException：对象引用未设置为对象的实例。 在 Microsoft.Azure.Documents.Document.get_AttachmentsLink() 在 Microsoft.Extensions.Internal.PropertyHelper.CallNullSafePropertyGetter[TDeclaringType,TValue]（Func`2 getter，对象目标） 在 Microsoft.AspNetCore.Mvc.Internal.DefaultComplexObjectValidationStrategy.Enumerator.MoveNext() 在 Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationVisitor.VisitChildren（IValidationStrategy 策略） 在 Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationVisitor.VisitComplexType() 在 Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationVisitor.Visit（ModelMetadata 元数据，字符串键，对象模型） 在 Microsoft.AspNetCore.Mvc.Internal.DefaultControllerArgumentBinder.d__8.MoveNext() --- 从先前抛出异常的位置结束堆栈跟踪 --- 在 System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() 在 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务） 在 Microsoft.AspNetCore.Mvc.Internal.DefaultControllerArgumentBinder.d__6.MoveNext() --- 从先前抛出异常的位置结束堆栈跟踪 --- 在 System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() 在 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务） 在 Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.d__22.MoveNext() --- 从先前抛出异常的位置结束堆栈跟踪 --- 在 System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() 在 Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Rethrow（ResourceExecutedContext 上下文） 在 Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.Next（状态&下一个，范围&范围，对象&状态，布尔& isCompleted） 在 Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.d__20.MoveNext() --- 从先前抛出异常的位置结束堆栈跟踪 --- 在 System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() 在 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务） 在 Microsoft.AspNetCore.Builder.RouterMiddleware.d__4.MoveNext() --- 从先前抛出异常的位置结束堆栈跟踪 --- 在 System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() 在 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务） 在 Microsoft.VisualStudio.Web.BrowserLink.BrowserLinkMiddleware.d__7.MoveNext() --- 从先前抛出异常的位置结束堆栈跟踪 --- 在 System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() 在 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务） 在 Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.d__7.MoveNext()

我尝试为与模型和 Microsoft.Azure.Documents.Document 关联的每个属性提供隐藏值的表单，但结果相同。另外，我将 POST 中的参数类型更改为动态，确实避免了异常。

TrainingModel（模型）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Newtonsoft.Json;

namespace Training.Models
{
    public class TrainingModel : Microsoft.Azure.Documents.Document
    {

    [JsonProperty(PropertyName = "text")]
    public string Text { get; set; }

    [JsonProperty(PropertyName = "last_updated")]
    public DateTime? LastUpdated { get; set; }

    [JsonProperty(PropertyName = "training_sentiment")]
    public string TrainingSentiment { get; set; }

    [JsonProperty(PropertyName = "sentiment")]
    public string Sentiment { get; set; }

    [JsonProperty(PropertyName = "score")]
    public string SentimentScore { get; set; }

    [JsonProperty(PropertyName = "entities")]
    public List<Entity> Entities { get; set; }

    public class Entity
    {

        [JsonProperty(PropertyName = "start")]
        public long Start { get; set; }

        [JsonProperty(PropertyName = "end")]
        public long End { get; set; }

        [JsonProperty(PropertyName = "value")]
        public string Value { get; set; }

        [JsonProperty(PropertyName = "orth")]
        public string Orth { get; set; }

        [JsonProperty(PropertyName = "label")]
        public string Label { get; set; }

        }

    }
}

文档（视图）

<form asp-controller="Tweet" asp-action="Document" method="post" asp-anti-forgery="false">

                            <!-- Tweet Text -->
                            <div class="form-group">
                                <label asp-for="Text" class="control-label">
                                    Document Text
                                </label>
                                <div class="well">
                                    @Html.Raw(Model.Text)
                                </div>
                            </div>

                            <!-- Entities -->
                            <div class="form-group tags">
                                <label asp-for="Entities">
                                    Name Entity Recognition
                                </label>
                                <div class="form-group">
                                    <p>Using your mouse, highlight some text in the document's text field to add entities to the document.</p>
                                </div>
                                <div class="form-group">
                                    <div class="col-md-2">
                                        <div>
                                            <label>
                                                Start
                                            </label>
                                        </div>
                                    </div>
                                    <div class="col-md-2">
                                        <div>
                                            <label>
                                                End
                                            </label>
                                        </div>
                                    </div>
                                    <div class="col-md-3">
                                        <div>
                                            <label>
                                                Label
                                            </label>
                                        </div>
                                    </div>
                                    <div class="col-md-4">
                                        <div>
                                            <label>
                                                Value
                                            </label>
                                        </div>
                                    </div>
                                    <div class="col-md-1">
                                        <div></div>
                                    </div>
                                </div>
                                @if(Model.Entities != null && Model.Entities.Count > 0) { 
                                    for (int i = 0; i < Model.Entities.Count; i++)
                                    {
                                        <div class="form-group row tag-row">
                                            <div class="col-md-2">
                                                <div>
                                                    @Html.TextBoxFor(model => model.Entities[i].Start, null, new { @class = "form-control" })
                                                </div>
                                            </div>
                                            <div class="col-md-2">
                                                <div>
                                                    @Html.TextBoxFor(model => model.Entities[i].End, null, new { @class = "form-control" })
                                                </div>
                                            </div>
                                            <div class="col-md-3">
                                                <div>
                                                    @Html.TextBoxFor(model => model.Entities[i].Label, null, new { @class = "form-control" })
                                                </div>
                                            </div>
                                            <div class="col-md-4">
                                                <div>
                                                    @Html.TextBoxFor(model => model.Entities[i].Value, null, new { @class = "form-control" })
                                                </div>
                                            </div>
                                            <div class="col-md-1">
                                                <div>
                                                    <button type="button" class="btn btn-default" data-toggle='tag-row'>
                                                        <i class='fa fa-trash-o'></i>
                                                    </button>
                                                </div>
                                            </div>
                                        </div>
                                    }
                                }
                            </div>

                            <!-- Sentiment Tag -->
                            <div class="form-group">
                                <label asp-for="TrainingSentiment" class="control-label">
                                    Sentiment Tag
                                </label>
                                <div>
                                    <div class="btn-toolbar" data-toggle="buttons">
                                        <div class="btn-group">
                                            <label class="btn btn-default @((Model.TrainingSentiment.ToLower() == "positive") ? "active" : string.Empty)">
                                                <input asp-for="TrainingSentiment" type="radio" value="positive" /> <span class="sentimentText">Positive</span>
                                            </label>
                                            <label class="btn btn-default @((Model.TrainingSentiment.ToLower() == "negative") ? "active" : string.Empty)">
                                                <input asp-for="TrainingSentiment" type="radio" value="negative" /> <span class="sentimentText">Negative</span>
                                            </label>
                                        </div>
                                        <div class="btn-group">
                                            <label class="btn btn-default">
                                                <input asp-for="TrainingSentiment" type="radio" value="" /> Reset
                                            </label>
                                        </div>
                                    </div>
                                </div>
                            </div>

                            <div class="ln_solid"></div>

                            <!-- Buttons -->
                            <div class="row text-center">
                                <button type="submit" class="btn btn-primary">Submit</button>
                            </div>

                            <!-- Hidden Data -->
                            <input asp-for="Id" type="hidden" />

                        </form>

TweetController

    public IActionResult Document()
    {
        var model = ConnectionModel.Tweets.SelectTagged(1)[0];
        return View(model);
    }

    [HttpPost]
    public IActionResult Document(TrainingModel model)
    {
        if (model == null)
            return Json(new { error = "null model." });


        return Json(model);
    }

Answer 1

您不应该从Microsoft.Azure.Documents.Document 扩展您的课程。此类本质上是对来自 Cosmos 服务的动态响应的包装，并包含您的实体不需要知道的属性（如 AttachmentLinks）。从您的模型中删除此基类，并考虑使用您自己的简单 DocumentBase 类。这样的事情可能会奏效。

public class DocumentBase
{
    [JsonProperty(PropertyName = "id")]
    public string Id { get; set; }
}