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Implement a custom configuration provider in .NET

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There are many configuration providers available for common configuration sources such as JSON, XML, and INI files. You may need to implement a custom configuration provider when one of the available providers doesn't suit your application needs. In this article, you'll learn how to implement a custom configuration provider that relies on a database as its configuration source.

Custom configuration provider

The sample app demonstrates how to create a basic configuration provider that reads configuration key-value pairs from a database using Entity Framework (EF) Core.

The provider has the following characteristics:

  • The EF in-memory database is used for demonstration purposes.
    • To use a database that requires a connection string, get a connection string from an interim configuration.
  • The provider reads a database table into configuration at startup. The provider doesn't query the database on a per-key basis.
  • Reload-on-change isn't implemented, so updating the database after the app has started will not affect the app's configuration.

Define a Settings record type entity for storing configuration values in the database. For example, you could add a Settings.cs file in your Models folder:

namespace CustomProvider.Example.Models;

public record Settings(string Id, string? Value);

For information on record types, see Record types in C#.

Add an EntityConfigurationContext to store and access the configured values.

Providers/EntityConfigurationContext.cs:

using CustomProvider.Example.Models;
using Microsoft.EntityFrameworkCore;

namespace CustomProvider.Example.Providers;

public sealed class EntityConfigurationContext(string? connectionString) : DbContext
{
    public DbSet<Settings> Settings => Set<Settings>();

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        _ = connectionString switch
        {
            { Length: > 0 } => optionsBuilder.UseSqlServer(connectionString),
            _ => optionsBuilder.UseInMemoryDatabase("InMemoryDatabase")
        };
    }
}

By overriding OnConfiguring(DbContextOptionsBuilder) you can use the appropriate database connection. For example, if a connection string was provided you could connect to SQL Server, otherwise you could rely on an in-memory database.

Create a class that implements IConfigurationSource.

Providers/EntityConfigurationSource.cs:

using Microsoft.Extensions.Configuration;

namespace CustomProvider.Example.Providers;

public sealed class EntityConfigurationSource(
    string? connectionString) : IConfigurationSource
{
    public IConfigurationProvider Build(IConfigurationBuilder builder) =>
        new EntityConfigurationProvider(connectionString);
}

Create the custom configuration provider by inheriting from ConfigurationProvider. The configuration provider initializes the database when it's empty. Since configuration keys are case-insensitive, the dictionary used to initialize the database is created with the case-insensitive comparer (StringComparer.OrdinalIgnoreCase).

Providers/EntityConfigurationProvider.cs:

using CustomProvider.Example.Models;
using Microsoft.Extensions.Configuration;

namespace CustomProvider.Example.Providers;

public sealed class EntityConfigurationProvider(
    string? connectionString)
    : ConfigurationProvider
{
    public override void Load()
    {
        using var dbContext = new EntityConfigurationContext(connectionString);

        dbContext.Database.EnsureCreated();

        Data = dbContext.Settings.Any()
            ? dbContext.Settings.ToDictionary(
                static c => c.Id,
                static c => c.Value, StringComparer.OrdinalIgnoreCase)
            : CreateAndSaveDefaultValues(dbContext);
    }

    static Dictionary<string, string?> CreateAndSaveDefaultValues(
        EntityConfigurationContext context)
    {
        var settings = new Dictionary<string, string?>(
            StringComparer.OrdinalIgnoreCase)
        {
            ["WidgetOptions:EndpointId"] = "b3da3c4c-9c4e-4411-bc4d-609e2dcc5c67",
            ["WidgetOptions:DisplayLabel"] = "Widgets Incorporated, LLC.",
            ["WidgetOptions:WidgetRoute"] = "api/widgets"
        };

        context.Settings.AddRange(
            [.. settings.Select(static kvp => new Settings(kvp.Key, kvp.Value))]);

        context.SaveChanges();

        return settings;
    }
}

An AddEntityConfiguration extension method permits adding the configuration source to the underlying ConfigurationManager instance.

Extensions/ConfigurationManagerExtensions.cs:

using CustomProvider.Example.Providers;

namespace Microsoft.Extensions.Configuration;

public static class ConfigurationManagerExtensions
{
    public static ConfigurationManager AddEntityConfiguration(
        this ConfigurationManager manager)
    {
        var connectionString = manager.GetConnectionString("WidgetConnectionString");

        IConfigurationBuilder configBuilder = manager;
        configBuilder.Add(new EntityConfigurationSource(connectionString));

        return manager;
    }
}

Since the ConfigurationManager is both an implementation of IConfigurationBuilder and IConfigurationRoot, the extension method can access the connection strings configuration and add the EntityConfigurationSource.

The following code shows how to use the custom EntityConfigurationProvider in Program.cs:

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Options;
using CustomProvider.Example;

HostApplicationBuilder builder = Host.CreateApplicationBuilder(args);

builder.Configuration.AddEntityConfiguration();

builder.Services.Configure<WidgetOptions>(
    builder.Configuration.GetSection("WidgetOptions"));

using IHost host = builder.Build();

WidgetOptions options = host.Services.GetRequiredService<IOptions<WidgetOptions>>().Value;
Console.WriteLine($"DisplayLabel={options.DisplayLabel}");
Console.WriteLine($"EndpointId={options.EndpointId}");
Console.WriteLine($"WidgetRoute={options.WidgetRoute}");

await host.RunAsync();
// Sample output:
//    WidgetRoute=api/widgets
//    EndpointId=b3da3c4c-9c4e-4411-bc4d-609e2dcc5c67
//    DisplayLabel=Widgets Incorporated, LLC.

Consume provider

To consume the custom configuration provider, you can use the options pattern. With the sample app in place, define an options object to represent the widget settings.

namespace CustomProvider.Example;

public class WidgetOptions
{
    public required Guid EndpointId { get; set; }

    public required string DisplayLabel { get; set; } = null!;

    public required string WidgetRoute { get; set; } = null!;
}

A call to Configure registers a configuration instance, which TOptions binds against.

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Options;
using CustomProvider.Example;

HostApplicationBuilder builder = Host.CreateApplicationBuilder(args);

builder.Configuration.AddEntityConfiguration();

builder.Services.Configure<WidgetOptions>(
    builder.Configuration.GetSection("WidgetOptions"));

using IHost host = builder.Build();

WidgetOptions options = host.Services.GetRequiredService<IOptions<WidgetOptions>>().Value;
Console.WriteLine($"DisplayLabel={options.DisplayLabel}");
Console.WriteLine($"EndpointId={options.EndpointId}");
Console.WriteLine($"WidgetRoute={options.WidgetRoute}");

await host.RunAsync();
// Sample output:
//    WidgetRoute=api/widgets
//    EndpointId=b3da3c4c-9c4e-4411-bc4d-609e2dcc5c67
//    DisplayLabel=Widgets Incorporated, LLC.

The preceding code configures the WidgetOptions object from the "WidgetOptions" section of the configuration. This enables the options pattern, exposing a dependency injection-ready IOptions<WidgetOptions> representation of the EF settings. The options are ultimately provided from the custom configuration provider.

See also