没有为此 DbContext 配置数据库提供程序。 可以通过覆盖 DbContext.OnConfiguring 来配置提供程序

Question

I have this database configuration to at my Startup class in .NET Core 3.1 Web Api project.

  public void ConfigureServices(IServiceCollection services)
  {
        var abcConnString = Configuration.GetConnectionString("abcConnString");
        services.RegisterAbcSqlServer<ABCContext>(abcConnString);

        var xyzConnString = Configuration.GetConnectionString("xyzConnString");
        services.RegisterXyzSqlServer<XYZContext>(xyzConnString);

        // code removed for brevity.
  }

and

public static class RegisterDbContext
{        
    public static void RegisterAbcSqlServer<T>(this IServiceCollection services, string connectionString)
        where T : DbContext, IAbcContext
    {
        var migrationsAssembly = typeof(RegisterDbContext).GetTypeInfo().Assembly.GetName().Name;
        services.AddDbContext<T>(options => options.UseSqlServer(connectionString, 
            sql => sql.MigrationsAssembly(migrationsAssembly))); 
    }

    public static void RegisterXyzSqlServer<T>(this IServiceCollection services, string connectionString)
                where T : DbContext, IXyzContext
    {
        var migrationsAssembly = typeof(RegisterDbContext).GetTypeInfo().Assembly.GetName().Name;
        services.AddDbContext<T>(options => options.UseSqlServer(connectionString,
            sql => sql.MigrationsAssembly(migrationsAssembly)));
    }
}

I can build without error. But when I perform EF Core add-migration, it hits error:

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. If AddDbContext is used, then also ensure that your DbContext type accepts a DbContextOptions object in its constructor and passes it to the base constructor for DbContext.

Answer 1

You can get this error when there is no way for the DI framework to configure the provider by injecting a DbContextOptions . So you just need to add a constructor that will accept one, or add a parameter for a DbContextOptions to be passed in. For example:

public class XYZContext : DbContext
{
    // Add this constructor
    public XYZContext (DbContextOptions options) : base(options)
    {
    }  

}