How to capture EF exception

Question

I want to capture the error from entity framework.

So i have the below code

 return await _context.SaveChangesAsync(cancellationToken);

if something goes wrong in the above code i want it to be captured as a warning in database, but as of now it is automatically saving in the database as error which has to be warning actually.

below is the error that i get

An exception occurred in the database while saving changes for context type 'ValuationsReporting.Models.ValuationsReportingContext'. System.InvalidOperationException: The property 'TemplateTypeId' on entity type 'ValuationFundTemplate' has a temporary value. Either set a permanent value explicitly or ensure that the database is configured to generate values for this property. at Microsoft.EntityFrameworkCore.Update.Internal.CommandBatchPreparer.Validate(ModificationCommand modificationCommand) at Microsoft.EntityFrameworkCore.Update.Internal.CommandBatchPreparer.BatchCommands(IReadOnlyList1 entries)+MoveNext() at Microsoft.EntityFrameworkCore.Update.Internal.BatchExecutor.ExecuteAsync(DbContext _, ValueTuple2 parameters, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.ExecuteImplementationAsync[TState,TResult](Func4 operation, Func4 verifySucceeded, TState state, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.Storage.ExecutionStrategy.ExecuteImplementationAsync[TState,TResult](Func4 operation, Func4 verifySucceeded, TState state, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(IReadOnlyList`1 entriesToSave, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(Boolean acceptAllChangesOnSuccess, CancellationToken cancellationToken)

System.InvalidOperationException

Microsoft.EntityFrameworkCore.Update

I tried using try catch but as soon as it goes to that line the error is logged in database.

Actual code :

try
                {
                    foreach (var template in snapshotDto.SnapshopFundTemplateDtos)
                    {
                        if (template.FundId != null)
                        {
                            foreach (var fundId in template.FundId)
                            {
                                var tempTemplate = allFundTemplates.Where(x => x.ValuationId == valuation.Id && x.FundId == fundId && x.TemplateTypeId == template.TemplateTypeId).FirstOrDefault();

                                //var tempTemplate = await _valuationFundTemplateRepository.GetOne(valuation.Id, fundId, template.TemplateTypeId, true, cancellationToken);
                                if (tempTemplate == null)
                                {
                                    tempTemplate = new ValuationFundTemplate();
                                    tempTemplate.CreatedBy = _userRepository.claimsPrincipal.Identity.Name;
                                    tempTemplate.CreatedOn = DateTime.Now.ToUniversalTime();
                                    isTemplateUpdate = false;
                                }
                                //tempTemplate.IsDeleted = false;
                                //if (template.IsDeleted)
                                //{
                                //     _valuationFundTemplateRepository.Delete(tempTemplate);
                                //}
                                //else
                                //{
                                //tempTemplate.IsDeleted = template.IsDeleted;

                                tempTemplate.IsDeleted = false;
                                tempTemplate.IsDefaultFundTemplate = template.IsDefault;
                                tempTemplate.FundId = fundId;
                                tempTemplate.ValuationId = valuation.Id;
                                tempTemplate.TemplateTypeId = 0;
                                tempTemplate.TemplateId = template.TemplateId;
                                tempTemplate.ModifiedBy = _userRepository.claimsPrincipal.Identity.Name;
                                tempTemplate.ModifiedOn = DateTime.Now.ToUniversalTime();
                                tempTemplates.Add(tempTemplate);
                                if (isTemplateUpdate)
                                {
                                    _valuationFundTemplateRepository.Update(tempTemplate);
                                }
                                else
                                {
                                    await _valuationFundTemplateRepository.Insert(tempTemplate, cancellationToken);
                                }
                                //  }

                                await _valuationFundTemplateRepository.SaveAsync(cancellationToken);//here is where the error occurs which i dont want to capture in database.
                                if (!isTemplateUpdate)
                                    valuation.ValuationFundTemplate.Add(tempTemplate);
                            }

                        }
                    }
                }catch(Exception e)
                {
                    var z = e.Message;
                }



public virtual async Task<int> SaveAsync(CancellationToken cancellationToken = default(CancellationToken))
        {
            return await _context.SaveChangesAsync(cancellationToken);
        }

Answer 1

Agreed with the @PrashantPimpale you can simply use try catch.

But for the advanced approach, I would suggest you can use a Global Error Handling Middleware. Through which you can capture any error occurred in the whole dotnet API/Application.

Just and Elaboration below:

// Extension method used to add the middleware to the HTTP request pipeline.
    public static class ErrorHandlingMiddlewareExtensions
    {
        public static IApplicationBuilder UseErrorHandlingMiddleware(this IApplicationBuilder builder)
        {
            return builder.UseMiddleware<ErrorHandlingMiddleware>();
        }
    }

Then add app.UseErrorHandlingMiddleware(); in the Startup's Configure() method.

You have to first create a ErrorHandlingMiddleware class.

 public class ErrorHandlingMiddleware
    {
        private readonly RequestDelegate _next;

        public ErrorHandlingMiddleware(RequestDelegate next)
        {
            _next = next;
        }

        public async Task Invoke(HttpContext httpContext)
        {
            try
            {
                await _next(httpContext);
            }
            catch (Exception ex)
            {
                await HandleExceptionAsync(httpContext, ex);
            }
        }

        private static async Task HandleExceptionAsync(HttpContext context, Exception exception)
        {
          // Implement how you want to handle the error.
        }
}