ASP.NET Core › Configuration & Options Pattern

How would you write a custom configuration provider to load settings from an unsupported source, like a remote configuration service or database?

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Answer

Implement IConfigurationSource (returning an IConfigurationProvider instance) and a corresponding ConfigurationProvider subclass overriding Load() to populate the provider's internal Data dictionary from your custom source, then register it via configurationBuilder.Add(new MyCustomSource()) -- integrating seamlessly with the rest of the configuration system, including layering with other providers and, if you implement change detection, triggering hot-reload.

public class DatabaseConfigurationProvider : ConfigurationProvider {
    public override void Load() {
        using var connection = new SqlConnection(_connectionString);
        var settings = connection.Query("SELECT [Key], [Value] FROM AppSettings");
        foreach (var s in settings) Data[s.Key] = s.Value;
    }
}

public class DatabaseConfigurationSource : IConfigurationSource {
    public IConfigurationProvider Build(IConfigurationBuilder builder) => new DatabaseConfigurationProvider();
}

Real-world example A multi-tenant SaaS platform builds a custom configuration provider that loads tenant-specific feature flags from a database table at startup, integrating seamlessly alongside the standard appsettings.json and environment variable providers.

Common follow-ups: How would you add live change detection (polling or push notifications) to this custom provider?;How does provider registration order affect precedence for a custom source?

Entity Framework Core & Data Access;Multiple Inheritance & MRO