Configuration

Package: Skymly.DesignPatterns.Extensions.Configuration

Maps IConfiguration string values to IStrategyRegistry<string, TContract> lookups — useful when a host selects a strategy implementation by configuration key instead of a hand-written switch.

Works with generated {Contract}Registry / {Contract}Keys from [RegisterStrategy] (see Strategy).

Install

Not included in the Skymly.DesignPatterns meta package:

dotnet add package Skymly.DesignPatterns.Extensions.Configuration --version 0.2.3-preview2

<PackageReference Include="Skymly.DesignPatterns.Extensions.Configuration" Version="0.2.3-preview2" />

Targets: netstandard2.0 and net8.0. Depends on Microsoft.Extensions.Configuration.Abstractions.

API

using DesignPatterns.Extensions.Configuration;
using Microsoft.Extensions.Configuration;

IConfiguration configuration = /* host configuration */;

// Throws RegistryConfigurationException when the key cannot be resolved.
var card = RegistryConfiguration.ResolveConfigured(
    CardMotionRegistry.Instance,
    configuration,
    configurationKey: "Card",
    defaultKey: CardMotionKeys.Alpha);

// Non-throwing variant.
if (RegistryConfiguration.TryResolveConfigured(
        CardMotionRegistry.Instance,
        configuration,
        "Card",
        out var motion,
        defaultKey: CardMotionKeys.Alpha))
{
    // use motion
}

Resolution order

1. Read IConfiguration[configurationKey].
2. When the value is missing or whitespace, use defaultKey when provided.
3. Call registry.TryGet(strategyKey, out implementation).

Prefer {Contract}Keys constants for defaultKey so call sites stay DP025-safe.

Failure messages

RegistryConfigurationException includes the configuration key, the configured value (or default), and the registry Keys list:

Configuration key 'Card' has value 'beta' which is not registered. Registered keys: alpha, gamma.

Host example

using DesignPatterns.Extensions.Configuration;
using Microsoft.Extensions.Configuration;

var configuration = new ConfigurationBuilder()
    .AddJsonFile("appsettings.json")
    .Build();

var card = RegistryConfiguration.ResolveConfigured(
    CardMotionRegistry.Instance,
    configuration,
    "Card",
    defaultKey: CardMotionKeys.Alpha);

Legacy App.config hosts

There is no dedicated ConfigurationManager.AppSettings extension package. Map AppSettings into IConfiguration in the host (an indexer adapter is enough for RegistryConfiguration), then call the same API.

See the PluginAssemblies sample host for a minimal adapter, and Samples for NuGet vs sibling consumption.

Related

• Strategy
• Dependency injection (Autofac / MSDI)
• Diagnostics (DP025, DP033)
• Maintainer notes: Configuration.md, PluginAssemblies.md