WPF Core - Connection Strings inside App.config Not Working

Question

Upon facing the said issue even followed the simple walkthrough at Connection Strings - EF Core but found out that while hardcoding the connectionstring as:

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)  
{  
    optionsBuilder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=Blogging;Trusted_Connection=True;");  
}  

leads to success, using the recommended approach of inserting an App.config file like:

<?xml version="1.0" encoding="utf-8"?>  
<configuration>  
  <connectionStrings>  
    <add name="BloggingDatabase"  
         connectionString="Server=(localdb)\mssqllocaldb;Database=Blogging;Trusted_Connection=True;" providerName="System.Data.SqlClient" />  
  </connectionStrings>  
</configuration>  

and updating the main code to:

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)  
{   optionsBuilder.UseSqlServer(ConfigurationManager.ConnectionStrings["BloggingDatabase"].ConnectionString);  
}  

is not successful, and following error being faced while carrying out migration:

System.NullReferenceException: Object reference not set to an instance of an object.  
   at Intro.BloggingContext.OnConfiguring(DbContextOptionsBuilder optionsBuilder) in C:\<...FileLocation...>\AppDbContext.cs:line 14  
   at Microsoft.EntityFrameworkCore.DbContext.get_InternalServiceProvider()  
   at Microsoft.EntityFrameworkCore.DbContext.Microsoft.EntityFrameworkCore.Infrastructure.IInfrastructure<System.IServiceProvider>.get_Instance()  
   at Microsoft.EntityFrameworkCore.Infrastructure.Internal.InfrastructureExtensions.GetService[TService](IInfrastructure`1 accessor)  
   at Microsoft.EntityFrameworkCore.Infrastructure.AccessorExtensions.GetService[TService](IInfrastructure`1 accessor)  
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(Func`1 factory)  
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(String contextType)  
   at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType)  
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType)  
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigration.<>c__DisplayClass0_0.<.ctor>b__0()  
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()  
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)  
Object reference not set to an instance of an object.  

What could be the reason behind the same?

Strange enough! Upon using the index technique i.e. like:

optionsBuilder.UseSqlServer(System.Configuration.ConfigurationManager.ConnectionStrings[0].ConnectionString);  

is successful but regretfully doesnot allow to update or remove-migration on the following complaint:

System.ArgumentException: Invalid value for key 'attachdbfilename'  

Thanks in advance for your reviewing and replying.

Answer 1

Hi,

Welcome to our Microsoft Q&A platform!

You need to make sure that the programName.exe.config file is generated in the bin directory so that ConfigurationManager can read it.

Thanks.

Answer 2

.NET Core applications do not honor app.config at all, but use different ways for configuration,

https://learn.microsoft.com/en-us/dotnet/core/run-time-config/

Answer 3

DI the connectionstring to the DBcontext in using EF Core from the appsettings.json file.

https://marcominerva.wordpress.com/2019/03/19/using-entity-framework-core-with-wpf-on-net-core-3-0/

https://learn.microsoft.com/en-us/ef/core/miscellaneous/configuring-dbcontext

HTH