Working implementation

RAIC.Extensions.Configuration.EntityFrameworkCore.SqlServer/README.md

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+# RAIC.Extensions.Configuration.EntityFrameworkCore.SqlServer
+
+This library enhances `RAIC.Extensions.Configuration.EntityFrameworkCore` with support for reload on update the via the
+[query change notifications](https://learn.microsoft.com/en-us/dotnet/framework/data/adonet/sql/query-notifications-in-sql-server) capability exposed by
+`Microsoft.Data.SqlClient.SqlDependency` along with SQL Server's 
+[Change Tracking](https://learn.microsoft.com/en-us/sql/relational-databases/track-changes/about-change-tracking-sql-server) feature.
+
+## Goals
+1. No polling!
+1. Updates happen in background via worker service (`IHostedService`)
+1. Only update settings which change rather than reloading all of them
+
+
+## Requirements
+* .NET 8
+
+## Gotchas
+* Won't work with Azure SQL until Microsoft adds/enables Service Broker support
+* Setting values cannot be `null` (as signified by the `RequiredAttribute` on `ISetting.Value`)
+
+## Known Issues
+* Not tested under load
+
+## Configuration Options
+There is a single property which can be configured (cf. the `SqlServerNotificationConfigurationReloaderOptions` POCO)
+1. `ConnectionString` - the full connection string for the SQL Server instance
+
+## Setup
+For `SqlServerNotificationConfigurationReloader` to work it requires Change Tracking to be enable on the `Settings` table (and therefore also on the database itself)
+eg:
+
+```sql
+ALTER DATABASE myDatabase
+SET CHANGE_TRACKING = ON (AUTO_CLEANUP = ON);
+
+ALTER TABLE dbo.Settings
+ENABLE CHANGE_TRACKING;
+```
+
+Reccommend adding your SQL to the migration which adds the `Settings` table/view (or a new migration if that table/view already exists).
+
+## Usage Example
+
+```csharp
+
+using RAIC.Extensions.Configuration.EntityFrameworkCore;
+using RAIC.Extensions.Configuration.EntityFrameworkCore.Extensions;
+using RAIC.Extensions.Configuration.EntityFrameworkCore.SqlServer.Extensions;
+
+[Table("settings", Schema = "dbo")] // Need to explicitly set schema somehow, this is one way to do it
+public record Setting : ISetting
+{
+    [Key]
+    public required string Key { get; set; }
+
+    [Required]
+    public required string Value { get; set; }
+}
+
+public class MyDbContext(DbContextOptions<MyDbContext> options) : DbContext(options), ISettingsDbContext<DbSet<Setting>,Setting>
+{
+    public DbSet<Setting> Settings { get; set; }
+}
+
+
+var builder = Host.CreateApplicationBuilder(args); // or  WebApplication.CreateBuilder(args); 
+
+// build an initial configuration
+builder.Configuration.AddJsonFile("appsettings.json")
+                     ...
+                     .AddUserSecrets<Program>(); // or wherever your connection string lives
+
+builder.Configuration.AddDbSet<MyDbContext, Setting>(dbContextOptions => dbContextOptions.UseSqlServer(builder.Configuration.GetConnectionString("Default")));
+
+...
+// Add the SqlServerNotificationConfigurationReloader background service and supporting services to obtain setting reloading functionalty
+builder.Services.AddSqlServerNotificationConfigurationReloadService<MyDbContext, Settings>(); // uses connection string from MyDbContext. Other overrides exist if this doesn't work for you - see cods docs
+
+await builder.Build().RunAsync(); // use config as normal
+
+```
+
+Read more about [Configuration](https://docs.microsoft.com/en-us/dotnet/core/extensions/configuration) and [Options](https://docs.microsoft.com/en-us/dotnet/core/extensions/options) on the Microsoft Docs site.