Working implementation

RAIC.Extensions.Configuration.EntityFrameworkCore.PostgreSQL/Extensions/ServiceCollectionExtensions.cs

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+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
+using Options = RAIC.Extensions.Configuration.EntityFrameworkCore.PostgreSQL.PostgreSQLNotificationConfigurationReloaderOptions;
+
+namespace RAIC.Extensions.Configuration.EntityFrameworkCore.PostgreSQL.Extensions;
+
+public static class ServiceCollectionExtensions
+{
+
+    public delegate OptionsBuilder<T> OptionsTransformer<T>(OptionsBuilder<T> transform) where T : class;
+
+
+    /// <summary>
+    /// Adds <see cref="PostgreSQLNotificationConfigurationReloader"/> (a <see cref="Microsoft.Extensions.Hosting.IHostedService"/> implementation)
+    /// and supporting services to the <see cref="IServiceCollection"/>.
+    /// </summary>
+    /// <typeparam name="TDbContext">Type of the <see cref="DbContext"/> to use to obtain the underlying database connection</typeparam>
+    /// <param name="services">The service collection to add the services too</param>
+    /// <returns>The service collection it was called on now with added services</returns>
+    public static IServiceCollection AddPostgreSQLNotificationConfigurationReloadService<TDbContext>(this IServiceCollection services)
+        where TDbContext : DbContext
+    {
+        return services.AddPostgreSQLNotificationConfigurationReloadService<TDbContext>(static _ => { });
+    }
+
+    /// <summary>
+    /// Adds <see cref="PostgreSQLNotificationConfigurationReloader"/> (a <see cref="Microsoft.Extensions.Hosting.IHostedService"/> implementation)
+    /// and supporting services to the <see cref="IServiceCollection"/>.
+    /// </summary>
+    /// <typeparam name="TDbContext">Type of the <see cref="DbContext"/> to use to obtain the underlying database connection</typeparam>
+    /// <param name="services">The service collection to add the services too</param>
+    /// <param name="configure">
+    /// Action to manually configure the <see cref="Options"/> instance consumed by <see cref="PostgreSQLNotificationConfigurationReloader"/> eg.
+    /// <code>
+    /// options => {
+    ///     options.DebounceInterval = TimeSpan.FromSeconds(2);
+    ///     options.ChannelName = "awesome_channel";
+    /// }
+    /// </code>
+    /// </param>
+    /// <returns>The service collection it was called on now with added services</returns>
+    public static IServiceCollection AddPostgreSQLNotificationConfigurationReloadService<TDbContext>(this IServiceCollection services, Action<Options> configure)
+        where TDbContext : DbContext
+    {
+        var optionsBuilder = services.AddCoreServices<TDbContext>();
+
+        optionsBuilder.Configure(configure);
+
+        return services;
+    }
+
+    /// <summary>
+    /// Adds <see cref="PostgreSQLNotificationConfigurationReloader"/> (a <see cref="Microsoft.Extensions.Hosting.IHostedService"/> implementation)
+    /// and supporting services to the <see cref="IServiceCollection"/>.
+    /// </summary>
+    /// <typeparam name="TDbContext">Type of the <see cref="DbContext"/> to use to obtain the underlying database connection</typeparam>
+    /// <param name="services">The service collection to add the services too</param>
+    /// <param name="optionsTransform">
+    /// Transformer delegate to apply to the <see cref="Options"/> instance consumed by <see cref="PostgreSQLNotificationConfigurationReloader"/> eg.
+    /// <code>
+    ///  optionsBuilder => optionsBuilder.Bind(context.Configuration)
+    /// </code>
+    /// </param>
+    /// <returns>The service collection it was called on now with added services</returns>
+    public static IServiceCollection AddPostgreSQLNotificationConfigurationReloadService<TDbContext>(this IServiceCollection services, OptionsTransformer<Options> optionsTransform)
+        where TDbContext : DbContext
+    {
+        var optionsBuilder = services.AddCoreServices<TDbContext>();
+
+        optionsTransform(optionsBuilder);
+
+        return services;
+    }
+
+
+    private static OptionsBuilder<Options> AddCoreServices<TDbContext>(this IServiceCollection services)
+        where TDbContext : DbContext
+    {
+        services.AddSingleton(static provider => provider.GetRequiredService<TDbContext>().Database)
+            .AddSingleton(static provider =>
+            {
+                var configRoot = (IConfigurationRoot)provider.GetRequiredService<IConfiguration>(); // DEBT: Is this cast always safe?
+                return configRoot.Providers.OfType<IEntityFrameworkCoreDbSetConfigurationProvider>().Single();
+            })
+            .AddHostedService<PostgreSQLNotificationConfigurationReloader>();
+
+        return services.AddOptions<Options>().ValidateDataAnnotations().ValidateOnStart();
+    }
+}
+
+
+/* 
+ * 
+CREATE OR REPLACE FUNCTION settings_poc.notify_setting_change()
+RETURNS trigger AS $$
+BEGIN
+PERFORM pg_notify('setting_channel', concat(NEW.key,'=',NEW.value));
+RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE OR REPLACE FUNCTION settings_poc.notify_setting_remove()
+RETURNS trigger AS $$
+BEGIN
+PERFORM pg_notify('setting_channel', OLD.key);
+RETURN OLD;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE TRIGGER setting_insert_trigger
+AFTER INSERT ON settings_poc.settings
+FOR EACH ROW EXECUTE FUNCTION settings_poc.notify_setting_change();
+
+CREATE TRIGGER setting_update_trigger
+AFTER UPDATE ON settings_poc.settings
+FOR EACH ROW WHEN (NEW.value <> OLD.value) EXECUTE FUNCTION settings_poc.notify_setting_change();
+
+CREATE TRIGGER setting_delete_trigger
+AFTER DELETE ON settings_poc.settings
+FOR EACH ROW EXECUTE FUNCTION settings_poc.notify_setting_remove();
+
+ * 
+ */