How to instantiate DbContext from IHostingService-CodePudding

I have a class that derives from BackgroundService (IHostedService) for running background tasks. This will be added to my services using builder.Services.AddHostedService<BackgroundTaskService>()

BackgroundService's task runs for the entire duration of the web application, checking for queued data to process.

My question is, how do I instantiate an instance of DbContext from this code?

I could have the BackgroundTaskService constructor accept a DbContext. But wouldn't that keep the DbContext open forever?

And how else could I instantiate it without duplicating all the code to scan my settings file for the connection string, etc.?

CodePudding user response：

You can use scope service factory. Check here for reference.

Here you have an example:

// Injection
public class DataApi : BackgroundService
{
  private readonly ILogger<DataApi> logger;
  private readonly IServiceScopeFactory scopeFactory;

  public DataApi(ILogger<DataApi> _logger, IConfiguration _cfg, IServiceScopeFactory _sSF)
  {
    logger = _logger;
    scopeFactory = _sSF;
    // e.g. data from appsettings.json 
    // var recovery = _cfg["Api:Recovery"];
  }
// ...

// Usage
protected async Task DataCollector()
{
  logger.LogInformation("Collector");

  using (var scope = scopeFactory.CreateScope())
  {
    var db = scope.ServiceProvider.GetRequiredService<MyDbContext>();

    var myList = await db.MyEntity
      .AsNoTracking()
      .Where(t => t.active)
      .ToListAsync();

    if (myList.Count == 0)
    {
      logger.LogInformation("Empty...");
      return;
    }
  // logic...
  }

  await Task.CompletedTask;
}

CodePudding user response：

The recemmended approach is to inject IDbContextFactory<TContext> as described in the following article:

Some application types (e.g. ASP.NET Core Blazor) use dependency injection but do not create a service scope that aligns with the desired DbContext lifetime. Even where such an alignment does exist, the application may need to perform multiple units-of-work within this scope. For example, multiple units-of-work within a single HTTP request.

In these cases, AddDbContextFactory can be used to register a factory for creation of DbContext instances.

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContextFactory<ApplicationDbContext>(
        options =>
            options.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=Test"));
}

Then in your controller:

private readonly IDbContextFactory<ApplicationDbContext> _contextFactory;

public MyController(IDbContextFactory<ApplicationDbContext> contextFactory)
{
    _contextFactory = contextFactory;
}

public void DoSomething()
{
    using (var context = _contextFactory.CreateDbContext())
    {
        // ...
    }
}