Develop Reference

How can to map to a wrapper class using Mapster?

Based on my project I need to create a wrapper for “IFormFile”, Actually I created a “AppFileProxy” class and “IAppFile” interface for this purpose :
IAppFile.cs :
public interface IAppFile
{
string Name { get; }
string FileName { get; }
string ContentType { get; }
long Length { get; }
void CopyTo(Stream target);
Task CopyToAsync(Stream target, CancellationToken cancellationToken = default);
Stream OpenReadStream();
}
AppFileProxy.cs :
public class AppFileProxy : IAppFile
{
private readonly IFormFile _formFile;
public AppFileProxy(IFormFile formFile)
{
_formFile = formFile ?? throw new ArgumentNullException(nameof(formFile));
}
public string Name => _formFile.Name;
public string FileName => _formFile.FileName;
public string ContentType => _formFile.ContentType;
public long Length => _formFile.Length;
public void CopyTo(Stream target)
{
_formFile.CopyTo(target);
}
public Task CopyToAsync(Stream target, CancellationToken cancellationToken = default)
{
return _formFile.CopyToAsync(target, cancellationToken);
}
public Stream OpenReadStream()
{
return _formFile.OpenReadStream();
}
}
Now, I want to Map “IFormFile” to “IAppFile” by using Mapster in the action controller as shown below :
CompanyDto.cs :
public class CompanyDto
{
public string Name { get; set; }
public IFormFile Logo { get; set; }
}
CompanyMapDto.cs :
public class CompanyMapDto : IRegister
{
public int Id { get; set; }
public string Name { get; set; }
public IAppFile Logo { get; set; }
public void Register(TypeAdapterConfig config)
{
config.ForType<CompanyDto, CompanyMapDto>()
.Map(dest => dest.Logo, src => new AppFileProxy(src.Logo));
}
}
action controller :
[HttpPost]
[Route("[controller]/[action]")]
public async Task<IActionResult> AddCompanyWithLogo([FromForm]CompanyDto dto)
{
CompanyMapDto company = dto.Adapt<CompanyMapDto>();
var stream = company.Logo.OpenReadStream();
return Ok();
}
But When I call action I get exception error for OpenReadStream() method :
System.NotImplementedException: The method or operation is not implemented.
at GeneratedType_1.OpenReadStream()
at MapsterInDotNet.Controllers.CompaniesController.AddCompanyWithLogo(CompanyDto dto) in C:\Users\Mohsen\source\repos\UseMapsterInDotNet\MapsterInDotNet\MapsterInDotNet\Controllers\CompaniesController.cs:line 52
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 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)
How do I resolve this?

Well. I managed to make it work. You have to explicitly configurate mapping from IAppFile to IFormFile.
So instead of your configuration:
config.ForType<CompanyDto, CompanyMapDto>()
.Map(dest => dest.Logo, src => new AppFileProxy(src.Logo));
Use this:
TypeAdapterConfig<IFormFile, IAppFile>.ForType() // Or NewConfig()
.MapWith(src => new AppFileProxy(src));

JWT: 'System.String' has three segments but is not in proper JWS format

I have an idToken string that is returned by google-sign-in use in mobile app with flutter and firebase:
Code in flutter
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/cupertino.dart';
import 'package:google_sign_in/google_sign_in.dart';
class Authentication {
static GoogleSignIn googleSignIn;
static Future<User> signInWithGoogle(BuildContext context) async {
FirebaseAuth auth = FirebaseAuth.instance;
User user;
googleSignIn = GoogleSignIn();
final GoogleSignInAccount googleSignInAccount = await googleSignIn.signIn();
if (googleSignInAccount != null) {
final GoogleSignInAuthentication googleSignInAuthentication =
await googleSignInAccount.authentication;
final AuthCredential credential = GoogleAuthProvider.credential(
accessToken: googleSignInAuthentication.accessToken,
idToken: googleSignInAuthentication.idToken,
);
try {
final UserCredential userCredential =
await auth.signInWithCredential(credential);
user = userCredential.user;
} on FirebaseAuthException catch (e) {
if (e.code == 'account-exists-with-different-credential') {
// handle the error here
} else if (e.code == 'invalid-credential') {
// handle the error here
}
} catch (e) {
// handle the error here
}
print("Credential token: ${credential.token}");
print("Credential provider id: ${credential.providerId}");
print("AccessToken: ${googleSignInAuthentication.accessToken}");
print("ID Token: ${googleSignInAuthentication.idToken}");
print("AccessToken.length: ${googleSignInAuthentication.accessToken.length}");
print("IdToken.length: ${googleSignInAuthentication.idToken.length}");
}
return user;
}
static Future signOut() async {
await googleSignIn.signOut();
FirebaseAuth.instance.signOut();
}
}
ID token is returned.
And I use this code to decode it:
public JwtPayload PayloadInfo(string idToken)
{
var jwtToken = new JwtSecurityToken(idToken);
JwtPayload payload = jwtToken.Payload;
return payload;
}
It works fine in the console app but with the .net 5 web API it fail with error:
System.ArgumentException: IDX12739: JWT: 'System.String' has three segments but is not in proper JWS format.
I research that my idToken is not in JWS type... and I don't know how to solve this.
Weirdly, the function PayloadInfo works fine in C# console app but in the web API, it doesn't.
Controller
[HttpPost("login-google")]
[MapToApiVersion("1.0")]
public async Task<IActionResult> GoogleLoginAsync(
[FromBody] ExternalAuthModel model)
{
if (ModelState.IsValid)
{
var result = await
_userService.GoogleExternalLoginAsync(model);
if (result.IsSuccess)
{
return Ok(result);
}
return BadRequest(result);
}
return BadRequest("Somethings going wrong...");
}
ExternalAuthModel
public class ExternalAuthModel
{
public string Provider { get; set; }
public string IdToken { get; set; }
}
GoogleExternalLoginAsync function in my Service
public async Task<UserManagerResponse> GoogleExternalLoginAsync(ExternalAuthModel model)
{
var payload = _jwtHandler.PayloadInfo(model.IdToken);
if (payload is null)
{
return new UserManagerResponse
{
Message = "Invalid google authentication.",
IsSuccess = false
};
}
var info = new UserLoginInfo(model.Provider, payload.Sub, model.Provider);
var user = await _userManager.FindByLoginAsync(info.LoginProvider, info.ProviderKey);
if (user is null)
{
user = await _userManager.FindByEmailAsync(payload["email"].ToString());
await _userManager.CreateAsync(user);
if (!await _roleManager.RoleExistsAsync(UserRoles.User))
await _roleManager.CreateAsync(new IdentityRole(UserRoles.User));
await _userManager.AddToRoleAsync(user, UserRoles.User);
await _userManager.AddLoginAsync(user, info);
}
else
{
await _userManager.AddLoginAsync(user, info);
}
if (user is null)
{
return new UserManagerResponse
{
Message = "Invalid google authentication.",
IsSuccess = false
};
}
var token = await _jwtHandler.GenerateToken(user);
return new UserManagerResponse
{
Message = token[0],
IsSuccess = true,
ExpireDate = DateTime.Parse(token[1])
};
}
PayloadInfo function
public JwtPayload PayloadInfo(string idToken)
{
// Exception when excute this line... it says my idToken is not in
// JWS compact format....
var jwtToken = new JwtSecurityToken(idToken);
JwtPayload payload = jwtToken.Payload;
return payload;
}
Log...
2021-07-04T16:10:30.3810628+07:00 [ERR] An unhandled exception has occurred while executing the request. (48a46595)
System.ArgumentException: IDX12739: JWT: 'System.String' has three segments but is not in proper JWS format.
at System.IdentityModel.Tokens.Jwt.JwtSecurityToken..ctor(String jwtEncodedString)
at FTask.AuthServices.Helpers.JwtHandler.PayloadInfo(String idToken) in D:\cn7\Project\hao\ftask\FTask.AuthServices\Helpers\JwtHandler.cs:line 83
at FTask.AuthServices.Services.UserService.GoogleExternalLoginAsync(ExternalAuthModel model) in D:\cn7\Project\hao\ftask\FTask.AuthServices\Services\UserService.cs:line 163
at FTask.Api.Controllers.AuthController.GoogleLoginAsync(ExternalAuthModel model) in D:\cn7\Project\hao\ftask\FTask.Api\Controllers\AuthController.cs:line 109
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 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()
--- End of stack trace from previous location ---
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_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.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.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)

Please test this:
public JwtPayload GetPayload()
{
var token = "<your token>";
var handler = new JwtSecurityTokenHandler();
var tokenData = handler.ReadJwtToken(token);
return tokenData.Payload;
}
i tested your token in .Net 5 Web API and got this result:

Creating a new comment only works once

I created a method for posting comments on a post. Everything works fine when I first post a comment. It appears under the post, it's saved in the database etc. However, if I want to create a second comment right away (without refreshing the page- because this way it does work) I get this error:
Microsoft.EntityFrameworkCore.Update: Error: An exception occurred in the database while saving changes for context type 'JoyAndFaithLicenta.Data.DataContext'.
Microsoft.EntityFrameworkCore.DbUpdateException: An error occurred while updating the entries. See the inner exception for details.
---> Microsoft.Data.SqlClient.SqlException (0x80131904): Cannot insert explicit value for identity column in table 'AspNetUsers' when IDENTITY_INSERT is set to OFF.
at Microsoft.Data.SqlClient.SqlCommand.<>c.<ExecuteDbDataReaderAsync>b__169_0(Task`1 result)
at System.Threading.Tasks.ContinuationResultTaskFromResultTask`2.InnerInvoke()
at System.Threading.Tasks.Task.<>c.<.cctor>b__274_0(Object obj)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location where exception was thrown ---
at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread)
at Microsoft.EntityFrameworkCore.Update.ReaderModificationCommandBatch.ExecuteAsync
(IRelationalConnection connection, CancellationToken cancellationToken) at
Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken) at
Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken) at
Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(IEnumerable`1 commandBatches, IRelationalConnection connection, CancellationToken cancellationToken) at
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(IList`1 entriesToSave, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(DbContext _, Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken) at
Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerExecutionStrategy.ExecuteAsync[TState,TResult](TState state, Func`4 operation, Func`4 verifySucceeded, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken) at
Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken) at JoyAndFaithLicenta.Data.UserRepository.SaveAllAsync() in C:\Users\Georgia\source\repos\JoyAndFaithLicenta\JoyAndFaithLicenta\Data\UserRepository.cs:line 84 at JoyAndFaithLicenta.Helpers.LogUserActivity.OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next) in C:\Users\Georgia\source\repos\JoyAndFaithLicenta\JoyAndFaithLicenta\Helpers\LogUserActivity.cs:line 30 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.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context) at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) at
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) at
Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker) 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 Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context) at JoyAndFaithLicenta.Middleware.ExceptionMiddleware.InvokeAsync(HttpContext context) in C:\Users\Georgia\source\repos\JoyAndFaithLicenta\JoyAndFaithLicenta\Middleware\ExceptionMiddleware.cs:line 33
Why is that? It's the only functionality where I have this problem. However, every other functionality has a SaveAsync() method created in the repository, and I have not created a repository for the comments, so I'm using DataContext: _context.SaveChangesAsync().
This is the method for posting a comment:
[HttpPost("create/{postId}")]
public async Task<ActionResult<CommentDto>> PostComment(CommentDto commentDto, int postId)
{
if (!ModelState.IsValid) return BadRequest("Not a valid model");
var user = await _userRepository.GetUserByUsernameAsync(User.GetUsername());
var comment = new Comment
{
PostId = postId,
UserId = user.Id,
Text = commentDto.Text,
Created = commentDto.Created,
User = commentDto.User
};
_context.Comments.Add(comment);
await _context.SaveChangesAsync();
return new CommentDto
{
PostId = comment.PostId,
UserId = comment.UserId,
Text = comment.Text,
Created = comment.Created,
User = comment.User
};
}
And this is the comment entity:
public class Comment
{
public int Id { get; set; }
public DateTime Created { get; set; } = DateTime.Now;
public string Text { get; set; }
[ForeignKey("UserId")]
public User User { get; set; }
public int UserId { get; set; }
[ForeignKey("PostId")]
public Post Post { get; set; }
public int? PostId { get; set; }
}

I can't see your onModelCreating function, but i think it is caused because you have not [Key] in your comment id.
public class Comment
{
[Key]
public int Id { get; set; }
public DateTime Created { get; set; } = DateTime.Now;
public string Text { get; set; }
[ForeignKey("UserId")]
public User User { get; set; }
public int UserId { get; set; }
[ForeignKey("PostId")]
public Post Post { get; set; }
public int? PostId { get; set; }
}
Then database will use Id as Key, and you are sure that keys aren't repeated.
Also, i think that you are injected DataContext service wrong.
Try to make the same job like this:
using(var cnx = new DataContext()
{
var comment = new Comment
{
PostId = postId,
UserId = user.Id,
Text = commentDto.Text,
Created = commentDto.Created,
User = commentDto.User
};
cnx.Comments.Add(comment);
await cnx.SaveChangesAsync();
}
If it works, its probplem with your DI in Startup.cs.
Remember, the best way to inject DataContext of EntityFramework is:
services.AddDbContext<DataContext>();

According to below code
var comment = new Comment
{
PostId = postId,
UserId = user.Id,
Text = commentDto.Text,
Created = commentDto.Created,
User = commentDto.User
};
You are trying to insert a new User as well. Since you are trying to create a new user with assigned ID you are getting this error. Because Aspnetuser table does not allow to pass ID explicitly since IDENTITY_INSERT is set to false by default.
I am not sure why you want to insert a user as well along with comment. Probably it can be a requirement. If you really want to create a user, then your User object should not have a assigned ID value.
If this is by mistake change User to UserId.

Polymorphic model binding for generic type parameter

I'm sending a partial object along with a file.
var formData = new FormData();
formData.append('model', JSON.stringify({ ... }));
formData.append('file', file, file.name)
// send formData to backend
My controller method is using Delta<T> from OData.
[HttpPatch("{id}")]
public async Task<IActionResult> Patch(
[FromRoute] Guid id,
[ModelBinder(BinderType = typeof(FormDataJsonBinder))] Delta<AbstractModel> model,
IFormFile file = null
)
However I'm not sending Delta<AbstractModel> as AbstractModel is an abstract class. So I'm really sending Delta<DerivedModel> or Delta<AnotherDerivedModel> etc...
My problem is that ASP.NET keeps throwing saying that it cannot cast to Delta<DerivedModel>
System.InvalidCastException: Unable to cast object of type 'Microsoft.AspNet.OData.Delta`1[DerivedModel]' to type 'Microsoft.AspNet.OData.Delta`1[AbstractModel]'.
at lambda_method308(Closure , Object , Object[] )
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 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.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
Here's my FormDataJsonBinder
public class FormDataJsonBinder : IModelBinder
{
public async Task BindModelAsync(ModelBindingContext bindingContext)
{
if (bindingContext == null) throw new ArgumentNullException(nameof(bindingContext));
// Fetch the value of the argument by name and set it to the model state
string fieldName = bindingContext.FieldName;
var valueProviderResult = bindingContext.ValueProvider.GetValue(fieldName);
if (valueProviderResult == ValueProviderResult.None) return Task.CompletedTask;
else bindingContext.ModelState.SetModelValue(fieldName, valueProviderResult);
// Do nothing if the value is null or empty
string value = valueProviderResult.FirstValue;
if (string.IsNullOrEmpty(value)) return Task.CompletedTask;
try
{
// Delta is a special case
if (bindingContext.ModelType.IsAssignableTo(typeof(Delta)))
{
var jsonObject = JObject.Parse(value);
// This extracts type T from Delta<T>
var innerModelType = bindingContext.ModelType.GenericTypeArguments.First();
if (jsonObject["#odata.type"] is not null)
{
var odataType = jsonObject["#odata.type"].Value<string>();
innerModelType = Type.GetType(odataType);
}
var innerModel = JsonConvert.DeserializeObject(value, innerModelType);
var deltaType = typeof(Delta<>).MakeGenericType(innerModelType);
var delta = Activator.CreateInstance(deltaType) as IDelta;
foreach (var property in jsonObject.Properties())
{
delta.TrySetPropertyValue(property.Name, innerModel.GetType().GetProperty(property.Name)?.GetValue(innerModel));
}
bindingContext.Result = ModelBindingResult.Success(delta);
}
else
{
// Deserialize the provided value and set the binding result
var result = JsonConvert.DeserializeObject(value, bindingContext.ModelType);
bindingContext.Result = ModelBindingResult.Success(result);
}
}
catch (JsonException)
{
bindingContext.Result = ModelBindingResult.Failed();
}
return Task.CompletedTask;
}
}
I also tried using a IModelBinderProvider as recommended here, but that also just throws "cannot cast to Delta<DerivedModel>"

The solution was to create the Delta object the right way.
var delta = Activator.CreateInstance(bindingContext.ModelType, innerModelType) as IDelta;

Threading issue when using IViewComponentHelper to convert ViewComponent to HTML string

I'm trying to use IViewComponentHelper in a multi threaded manner. But it's throwing :( (see full exception at bottom of post)
System.NullReferenceException: Object reference not set to an instance of an object.
at Microsoft.AspNetCore.Http.DefaultHttpContext.get_Items()
I have no idea why.
Here's my setup: (simplified for brevity)
Controller:
public async Task<IActionResult> Get()
{
var pdfStream = await _pdfService.GenerateAsync();
return File(pdfStream, "application/pdf");
}
PdfService:
public class PdfService
{
private readonly PdfSDK _pdfSDK;
public constructor(PdfSDK pdfSDK)
{
_pdfSDK = pdfSDK;
}
public async Task<Stream> GenerateAsync()
{
List<Task<PdfDocument>> tasks = await _context.Foos.Select(x => DoWorkAsync(x));
var pdfs = await Task.WhenAll(tasks);
var mergedPdf = _pdfSDK.MergePdfs(pdfs);
return mergedPdf.Stream;
}
private async Task<PdfDocument> DoWorkAsync(Foo foo)
{
var html = await _renderViewComponentService.RenderViewComponentAsStringAsync<MyViewComponent>(foo);
var document = await _pdfSDK.HtmlToDocumentAsync(html);
return document;
}
}
PdfSDK:
public class PdfSDK
{
public async Task<PdfDocument> HtmlToDocumentAsync(string html)
{
using var pdfEngine = new PdfEngine();
var pdf = await pdfEngine.HtmlAsPdfAsync(html);
return pdf;
}
public PdfDocument MergePdfs(params PdfDocument[] pdfs)
{
var pdf = PdfDocument.Merge(pdfs);
return pdf;
}
}
MyViewComponent:
public class MyViewComponent : ViewComponent
{
public IViewComponentResult Invoke(Foo args)
{
return View(args);
}
}
Default.cshtml
#model Foo
<h1>Hello from #Foo.Id<h1>
RenderViewComponentService:
public class RenderViewComponentService
{
private readonly IServiceProvider _serviceProvider;
private readonly ITempDataProvider _tempDataProvider;
private readonly IViewComponentHelper _viewComponentHelper;
public RenderViewComponentService(
IServiceProvider serviceProvider,
ITempDataProvider tempDataProvider,
IViewComponentHelper viewComponentHelper
)
{
_serviceProvider = serviceProvider;
_tempDataProvider = tempDataProvider;
_viewComponentHelper = viewComponentHelper;
}
public async Task<string> RenderViewComponentAsStringAsync<TViewComponent>(object args)
where TViewComponent : ViewComponent
{
var viewContext = GetFakeViewContext();
(_viewComponentHelper as IViewContextAware).Contextualize(viewContext);
// this appears to call InvokeAsync in TViewComponent, but it'll also call Invoke (synchronously) if it's implemented
// see https://learn.microsoft.com/en-us/aspnet/core/mvc/views/view-components?view=aspnetcore-3.1#perform-synchronous-work
var htmlContent = await _viewComponentHelper.InvokeAsync<TViewComponent>(args); // exception is thrown here!
using var stringWriter = new StringWriter();
htmlContent.WriteTo(stringWriter, HtmlEncoder.Default);
var html = stringWriter.ToString();
return html;
}
private ViewContext GetFakeViewContext(ActionContext actionContext = null, TextWriter writer = null)
{
actionContext ??= GetFakeActionContext();
var viewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary());
var tempData = new TempDataDictionary(actionContext.HttpContext, _tempDataProvider);
var viewContext = new ViewContext(
actionContext,
NullView.Instance,
viewData,
tempData,
writer ?? TextWriter.Null,
new HtmlHelperOptions());
return viewContext;
}
private ActionContext GetFakeActionContext()
{
var httpContext = new DefaultHttpContext
{
RequestServices = _serviceProvider,
};
var routeData = new RouteData();
var actionDescriptor = new ActionDescriptor();
return new ActionContext(httpContext, routeData, actionDescriptor);
}
private class NullView : IView
{
public static readonly NullView Instance = new NullView();
public string Path => string.Empty;
public Task RenderAsync(ViewContext context)
{
if (context == null) { throw new ArgumentNullException(nameof(context)); }
return Task.CompletedTask;
}
}
}
Exception:
fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
An unhandled exception has occurred while executing the request.
System.NullReferenceException: Object reference not set to an instance of an object.
at Microsoft.AspNetCore.Http.DefaultHttpContext.get_Items()
at Microsoft.AspNetCore.Mvc.Routing.UrlHelperFactory.GetUrlHelper(ActionContext context)
at Microsoft.AspNetCore.Mvc.Razor.RazorPageActivator.<>c__DisplayClass4_0.<.ctor>b__0(ViewContext context)
at Microsoft.Extensions.Internal.PropertyActivator`1.Activate(Object instance, TContext context)
at Microsoft.AspNetCore.Mvc.Razor.RazorPagePropertyActivator.Activate(Object page, ViewContext context)
at Microsoft.AspNetCore.Mvc.Razor.RazorPageActivator.Activate(IRazorPage page, ViewContext context)
at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageCoreAsync(IRazorPage page, ViewContext context)
at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageAsync(IRazorPage page, ViewContext context, Boolean invokeViewStarts)
at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderAsync(ViewContext context)
at Microsoft.AspNetCore.Mvc.ViewComponents.ViewViewComponentResult.ExecuteAsync(ViewComponentContext context)
at Microsoft.AspNetCore.Mvc.ViewComponents.DefaultViewComponentInvoker.InvokeAsync(ViewComponentContext context)
at Microsoft.AspNetCore.Mvc.ViewComponents.DefaultViewComponentHelper.InvokeCoreAsync(ViewComponentDescriptor descriptor, Object arguments)
at MyProject.Services.RenderViewComponentService.RenderViewComponentToStringAsync[TViewComponent](Object args) in MyProject\Services\RenderViewComponentService.cs:line ??
at MyProject.Services.PdfService.DoWorkAsync(Foo foo) in MyProject\Services\PdfService.cs:line ??
at MyProject.Services.PdfService.GenerateAsync() in MyProject\Services\PdfService.cs:line ??
at MyProject.Controllers.MyController.Get() in MyProject\Controllers\MyController.cs:line ??
at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.<InvokeActionMethodAsync>g__Awaited|12_0(ControllerActionInvoker invoker, ValueTask`1 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.<InvokeNextResourceFilter>g__Awaited|24_0(ResourceInvoker invoker, Task
lastTask, State next, Scope scope, Object state, Boolean isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|19_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.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
at Microsoft.AspNetCore.HeaderPropagation.HeaderPropagationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)
I think the problem is how I Contextualize the IViewComponentHelper. But I'm at a loss on how else to do it.
Can you spot anything I'm doing wrong?