# 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 a [hosted service](https://learn.microsoft.com/en-us/aspnet/core/fundamentals/host/hosted-services) implementation
1. Only update settings which change rather than updating them all


## 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`)
* Consider adding `ConnectRetryCount` and `ConnectRetryInterval` [parameters](https://learn.microsoft.com/en-us/dotnet/framework/data/adonet/whats-new#sqlclient-data-provider) to your connection string if not already present

## Known Issues
* Not tested under load
* Transient failure detection logic is not well tested given the challenges in reproducing these issues

## Configuration Options
There are two properties which can be configured (cf. the `SqlServerNotificationConfigurationReloaderOptions` POCO)
1. `ConnectionString` - the full connection string for the SQL Server instance
1. `TransientErrors` - the list of `SqlError.Number` values that will be treated as transient if present in a thrown `SqlException`'s `Errors` collection while listening for or processing notifications (ie. reconnection will be attempted if any are present)

## 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;
```

Recommend 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>>, ISettingsDbContextFactory<MyDbContext>
{
    public DbSet<Setting> Settings { get; set; }

    public static MyDbContext Create(DbContextOptions<MyDbContext> options) => new(options);
}


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.AddDbContext<MyDbContext>(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.