Using a Scoped service in a Singleton in an Asp.Net Core app

Question

In my Asp.Net Core App I need a singleton service that I can reuse for the lifetime of the application. To construct it, I need a DbContext (from the EF Core), but

Answer 1

Looking at the name of this service - I think what you need is a custom configuration provider that loads configuration from database at startup (once only). Why don't you do something like following instead? It is a better design, more of a framework compliant approach and also something that you can build as a shared library that other people can also benefit from (or you can benefit from in multiple projects).

public class Program
{
    public static void Main(string[] args)
    {
        CreateWebHostBuilder(args).Build().Run();
    }

    public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
                .UseStartup()
                .ConfigureAppConfiguration((context, config) =>
                {
                    var builtConfig = config.Build();
                    var persistentConfigBuilder = new ConfigurationBuilder();
                    var connectionString = builtConfig["ConnectionString"];
                    persistentStorageBuilder.AddPersistentConfig(connectionString);
                    var persistentConfig = persistentConfigBuilder.Build();
                    config.AddConfiguration(persistentConfig);
                });
}

Here - AddPersistentConfig is an extension method built as a library that looks like this.

public static class ConfigurationBuilderExtensions
{
    public static IConfigurationBuilder AddPersistentConfig(this IConfigurationBuilder configurationBuilder, string connectionString)
    {
          return configurationBuilder.Add(new PersistentConfigurationSource(connectionString));
    }

}

class PersistentConfigurationSource : IConfigurationSource
{
    public string ConnectionString { get; set; }

    public PersistentConfigurationSource(string connectionString)    
    {
           ConnectionString = connectionString;
    }

    public IConfigurationProvider Build(IConfigurationBuilder builder)
    {
         return new PersistentConfigurationProvider(new DbContext(ConnectionString));
    }

}

class PersistentConfigurationProvider : ConfigurationProvider
{
    private readonly DbContext _context;
    public PersistentConfigurationProvider(DbContext context)
    {
        _context = context;
    }


    public override void Load() 
    {
           // Using _dbContext
           // Load Configuration as valuesFromDb
           // Set Data
           // Data = valuesFromDb.ToDictionary...
    }

}