c# - 为什么会出现 "Could not create an instance of type Microsoft.AspNetCore.Http.IFormFile"错误？

Question

我得到了这个非常有用的错误。但是找不到问题。

{"ClassName":"Newtonsoft.Json.JsonSerializationException","Message":"Could not create an instance of type Microsoft.AspNetCore.Http.IFormFile. Type is an interface or abstract class and cannot be instantiated. Path 'file.ContentDisposition', line 1, position 63.","Data":null,"InnerException":null,"HelpURL":null,"StackTraceString":"   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateNewObject(JsonReader reader, JsonObjectContract objectContract, JsonProperty containerMember, JsonProperty containerProperty, String id, Boolean& createdFromNonDefaultCreator)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.SetPropertyValue(JsonProperty property, JsonConverter propertyConverter, JsonContainerContract containerContract, JsonProperty containerProperty, JsonReader reader, Object target)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(Object newObject, JsonReader reader, JsonObjectContract contract, JsonProperty member, String id)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)\r\n   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)\r\n   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)\r\n   at Newtonsoft.Json.JsonSerializer.Deserialize(JsonReader reader, Type objectType)\r\n   at Newtonsoft.Json.JsonSerializer.Deserialize[T](JsonReader reader)\r\n   at Microsoft.Azure.Cosmos.CosmosJsonDotNetSerializer.FromStream[T](Stream stream)\r\n   at Microsoft.Azure.Cosmos.CosmosJsonSerializerWrapper.FromStream[T](Stream stream)\r\n   at Microsoft.Azure.Cosmos.CosmosSerializerCore.FromStream[T](Stream stream)\r\n   at Microsoft.Azure.Cosmos.CosmosResponseFactoryCore.ToObjectpublic[T](ResponseMessage responseMessage)\r\n   at Microsoft.Azure.Cosmos.CosmosResponseFactoryCore.<CreateItemResponse>b__8_0[T](ResponseMessage cosmosResponseMessage)\r\n   at Microsoft.Azure.Cosmos.CosmosResponseFactoryCore.ProcessMessage[T](ResponseMessage responseMessage, Func`2 createResponse)\r\n   at Microsoft.Azure.Cosmos.CosmosResponseFactoryCore.CreateItemResponse[T](ResponseMessage responseMessage)\r\n   at Microsoft.Azure.Cosmos.ContainerCore.CreateItemAsync[T](CosmosDiagnosticsContext diagnosticsContext, T item, Nullable`1 partitionKey, ItemRequestOptions requestOptions, CancellationToken cancellationToken)\r\n   at Microsoft.Azure.Cosmos.ClientContextCore.RunWithDiagnosticsHelperAsync[TResult](CosmosDiagnosticsContext diagnosticsContext, Func`2 task)\r\n   at SmartLearning_salon.Services.Person.PersonService.AddItemAsync(Person person) in C:\\Users\\knoer\\source\\repos\\SmartLearning_salon\\SmartLearning_salon\\Services\\Person\\PersonService.cs:line 25\r\n   at SmartLearning_salon.Controllers.PersonController.Create(Person person) in C:\\Users\\knoer\\source\\repos\\SmartLearning_salon\\SmartLearning_salon\\Controllers\\PersonController.cs:line 67","RemoteStackTraceString":null,"RemoteStackIndex":0,"ExceptionMethod":null,"HResult":-2146233088,"Source":"Newtonsoft.Json","WatsonBuckets":null}

我的 ASP.NET MVC 应用程序中的 Controller 首先将文件发送到 Azure 存储，然后将记录添加到 Cosmos DB。文件和记录都已正确保存/存储。但是保存页面后返回以下错误 “无法创建 Microsoft.AspNetCore.Http.IFormFile 类型的实例”

我知道不可能从接口(interface)实例化对象，但这是在哪里发生的？

在我的 ASP.NET MVC Core 3.1 中，我有一个看起来像这样的模型

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

    [JsonProperty(PropertyName = "name")]
    public string Name { get; set; }

    [JsonProperty(PropertyName = "ssn")]
    public string Ssn { get; set; }

    //[JsonProperty(PropertyName = "testresult")]
    //public bool TestResult { get; set; }

    [JsonProperty(PropertyName = "file")]
    public IFormFile File { get; set; }

}

我的 PersonController 看起来像这样

        // POST: PersonController/Create
        [HttpPost]
        [ValidateAntiForgeryToken]
        public  async Task<ActionResult> Create(Person person)
        {
            using (var stream = new MemoryStream())
            {
                try
                {
                    // assume a single file POST
                    await person.File.CopyToAsync(stream);
                    stream.Seek(0, SeekOrigin.Begin);

                    // now send blob up to Azure
                    await _blobStorageService.CreateBlobAsync(person.File.OpenReadStream(), person.File.FileName);

                    // send to Cosmos
                    await _personService.AddItemAsync(person);

                    //Ændre dette til at returnere et til detail view
                    return View("Person");
                    //return Ok(new { fileuploaded = true });
                }
                catch (Exception ex)
                {
                    return BadRequest(ex);
                }
            }

        }

我的个人服务

        public async Task AddItemAsync(Models.Person person)
        {
            await container.CreateItemAsync(person, new PartitionKey(person.Id));
        }

我的存储服务

  public async Task CreateBlobAsync(Stream stream, string filename)
        {
            try
            {
                //Opret hvis ikkke eksisterer
                await bcc.CreateIfNotExistsAsync();

                await bcc.UploadBlobAsync(filename, stream);
            }
            catch (Exception)
            {

                throw;
            }

        }

我真的很感激我能得到的所有帮助。

谢谢克劳斯

Answer 1

IFormFile 是一个接口(interface)。它们不能在没有上下文的情况下创建。

您正在尝试使用 Person 的表单编码版本来建模数据存储。

您应该有两个独立的模型:一个用于表单提交，另一个用于数据存储:

public class PersonForm
{
    public string Id { get; set; }
    public string Name { get; set; }
    public string Ssn { get; set; }
    public IFormFile File { get; set; }
}

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

    [JsonProperty("name")]
    public string Name { get; set; }

    [JsonProperty("ssn")]
    public string Ssn { get; set; }

    [JsonProperty("fileName")]
    public string FileName { get; set; }
}

那么您的端点将如下所示:

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<ActionResult> Create([FromForm] PersonForm personForm)
{
    try
    {
        // now send blob up to Azure
        await _blobStorageService.CreateBlobAsync(
            personForm.File.OpenReadStream(), personForm.File.FileName);

        // send to Cosmos
        await _personService.AddItemAsync(new Person
        {
            Id = personForm.Id,
            Name = personForm.Name,
            Ssn = personForm.Ssn,
            FileName = personForm.File.FileName
        });

        //Ændre dette til at returnere et til detail view
        return View("Person");
    }
    catch (Exception ex)
    {
        return BadRequest(ex);
    }
}

当许多属性相同时，您可以使用 AutoMapper 来更轻松地复制 DTO 对象。