Entity Framework Core - Migration - No Parameterless Constructor Defined for this Object

Design-time tools attempt to automatically find how your application creates instances of your DbContext type. If EF cannot find a suitable way to initialize your DbContext, you may encounter this error.

Options: 1- Either create a parameterless constructor

  public AlmanacDb() { }
  protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
  {           
       optionsBuilder.UseSqlServer(_connString);
  }

  private readonly string _connString = "<your conn string>";

2-

public AlmanacDb Create()
{
     var optionsBuilder = new DbContextOptionsBuilder<AlmanacDb>();
     optionsBuilder.UseSqlServer(connectionString);

     return new AlmanacDb(optionsBuilder.Options);
}

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

If you have a separate project for context. set a startup project with the target project

dotnet ef migrations add InitialCreate -s .\src\WebUI\  -p .\src\Infrastructure\ --verbose