Why do I Get an "Could not create an instance of type Microsoft.AspNetCore.Http.IFormFile" error?

user_1754132 0
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I get this really informative error. But cannot find the issue.

{"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}

The controller in my ASP.NET MVC app first sends a file to Azure Storage and then add a record to Cosmos DB. Both file and the record are saved/stored correctly. But then after save the page returns with the following error "Could not create an instance of type Microsoft.AspNetCore.Http.IFormFile"

I know that it is not possible to instantiate an object from an interface, but where is this happening?

In my ASP.NET MVC Core 3.1 I have a model that looks like this

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; }

}

My PersonController looks like this

        // 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);
                }
            }

        }

My PersonService

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

My StorageService

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

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

                throw;
            }

        }

I really appriciate all the help that I can get.

Thanks Klaus

razor model-view-controller asp.net c#
1 Answers

IFormFile is an interface. They can't be created without context.

You are trying to use your form-encoded version of Person to model data storage.

You should have two separate models: one for your form submission, the other for your data storage:

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; }
}

Then your endpoint would look like this:

[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);
    }
}

You could make use of AutoMapper to make it much easier to copy over DTO objects when a lot of the properties are the same.

user_12041530
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