没有注册类型“类型”的服务

Question

I have a database context that I am registering and seeding. However, I get the error:

System.InvalidOperationException: 'No service for type 'AnnouncementContext' has been registered.'

DB registering/seeding

private static void SeedDatabase(IHost host)
        {
            var scopeFactory = host.Services.GetRequiredService<IServiceScopeFactory>();
            using var scope = scopeFactory.CreateScope();
            var announcementContext = scope.ServiceProvider.GetRequiredService<AnnouncementContext>(); // exception occurs here

            if (announcementContext.Database.EnsureCreated()) {
                try {
                    SeedData.Initialize(announcementContext);
                }
                catch (Exception ex) {
                    var logger = scope.ServiceProvider.GetRequiredService<ILogger<Program>>();
                    logger.LogError(ex, "A database seeding error occurred.");
                    ErrorLogger.logError(ex);
                }
            }
        }

Context class

public class AnnouncementContext : DbContext {
        public AnnouncementContext(DbContextOptions<AnnouncementContext> options)
            : base(options) {
        }

        public DbSet<Announcement> Announcements { get; set; }
    }

What is causing this error and how can I fix it?

Answer 1

The code in your DB registering/seeding section is not registering any DB or DbContext. It is trying to get a reference of already registered DbContext (in your case AnnouncementContext ). So, the question is, have you already registered it? The error message indicates, you have not.

In most common scenario, you are supposed to register the AnnouncementContext in the ConfigureServices() method of the Startup class like -

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers();

    // this is the DbContext registration code
    services.AddDbContext<AnnouncementContext>(
        options => options.UseSqlServer("name=ConnectionStrings:DefaultConnection"));
}

For more on this - DbContext in dependency injection for ASP.NET Core