How to fix “No database provider has been configured for this DbContext” in EF Core?

Time needed: 5 minutes

How to fix “No database provider has been configured for this DbContext. A provider can be configured by overriding the DbContext.OnConfiguring method or by using AddDbContext on the application service provider.”?

1. Make sure you’re running the Add-Migration commandlet against the right project

   Depending on your project configuration, you’ll need to run your Add-Migration command against a project where you instantiate your DBContext, perhaps with the project hosting your DBContext as your startup project and/or working directory.
   
   You can see the details on how to verify most of the details here:
   https://www.koskila.net/an-assembly-specified-in-the-application-dependencies-manifest-was-not-found-when-running-add-migration-in-entity-framework-core/
2. Override the OnConfiguring method

   In your DbContext class, add something like this:
   
   protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
// You don't actually ever need to call this
}
   
   This overridden method call will get called when your context gets instantiated (when running Add-Migration, anyone) – but you’ll then need to next configure the actual provider for this context.

3. Add a call to your preferred database provider

   This can be mocked – just have something like the below in the OnConfiguring call:
   
   optionsBuilder.UseSqlServer(@”Server=(localdb)\mssqllocaldb;Database=Contoso-dev”);
   
   Add-Migration won’t actually use this. And as long as the overridden method call isn’t called by you, this connection string won’t be used then, either. Or you could always add some logic around it to not actually use it.
   
   You could even do something like the below:
   
   protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
if (!optionsBuilder.IsConfigured)
{
optionsBuilder.UseNpgsql(
"Host=TimescaleDB;Port=5432;Database=valutecdb;Username=postgres;Password=pwd");
}
}