Create DBContext outside of DependencyInjection

Question

I'm creating an ASP.NET Core application. It is using Entity Framework Core for database access. I'm using services.AddDbContext in Startup.cs and the DB Context is injected into my controller as expected.

I am also have a background task using IHostedService that is added as a Singleton. I'd like to have an instance of my DBContext in my implementation of IHostedService. When I try to do this I get a run time error that my IHostedService cannot consume a scoped service (my DB Context).

The DB Context class takes a parameter of DbContextOptions options and passes the options to the base constructor (DbContext).

I need to create an instance of my DB Context in my implementation of IHostedService (a singleton object) but I can't seem to figure out how to correctly create a new instance of DbContextOptions from my IHostedService implementation.

Show how you add hosted service – Nkosi Sep 11 '18 at 01:53 — Nkosi, Sep 11 '18 at 01:53

score 2 · Accepted Answer · answered Sep 11 '18 at 02:17

For resolving a Scoped Service from a Singleton Service, you could create the scoped service from IServiceProvider.

Here is the demo code:

    public class DbHostedService : IHostedService
{
    private readonly ILogger _logger;

    public DbHostedService(IServiceProvider services,
        ILogger<DbHostedService> logger)
    {
        Services = services;
        _logger = logger;
    }

    public IServiceProvider Services { get; }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation(
            "Consume Scoped Service Hosted Service is starting.");

        DoWork();

        return Task.CompletedTask;
    }

    private void DoWork()
    {
        _logger.LogInformation(
            "Consume Scoped Service Hosted Service is working.");

        using (var scope = Services.CreateScope())
        {
            var context =
                scope.ServiceProvider
                    .GetRequiredService<ApplicationDbContext>();

            var user = context.Users.LastOrDefault();

            _logger.LogInformation(user?.UserName);
        }
    }

    public Task StopAsync(CancellationToken cancellationToken)
    {
        _logger.LogInformation(
            "Consume Scoped Service Hosted Service is stopping.");

        return Task.CompletedTask;
    }
}

Reference: Consuming a scoped service in a background task

score -1 · Answer 2 · answered Sep 10 '18 at 20:17

-1

I think you need not IHostedService. Myeby your need this

public void ConfigureServices(IServiceCollection services)
    {
        services.AddDbContext<BlogContext>(options =>

       options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

        services.AddMvc();
        services.AddSession();
    }

answered Sep 10 '18 at 20:17

FX_Sektor

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That code you have is what I am using. The IHostedService is for a different purpose but still needs the DBContext – James Sep 10 '18 at 20:23

Create DBContext outside of DependencyInjection

2 Answers2