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1 change: 1 addition & 0 deletions docs/README.instructions.md
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Expand Up @@ -99,6 +99,7 @@ See [CONTRIBUTING.md](../CONTRIBUTING.md#adding-instructions) for guidelines on
| [DevOps Core Principles](../instructions/devops-core-principles.instructions.md)<br />[![Install in VS Code](https://img.shields.io/badge/VS_Code-Install-0098FF?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fdevops-core-principles.instructions.md)<br />[![Install in VS Code Insiders](https://img.shields.io/badge/VS_Code_Insiders-Install-24bfa5?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fdevops-core-principles.instructions.md) | Foundational instructions covering core DevOps principles, culture (CALMS), and key metrics (DORA) to guide GitHub Copilot in understanding and promoting effective software delivery. |
| [Dotnet Wpf](../instructions/dotnet-wpf.instructions.md)<br />[![Install in VS Code](https://img.shields.io/badge/VS_Code-Install-0098FF?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fdotnet-wpf.instructions.md)<br />[![Install in VS Code Insiders](https://img.shields.io/badge/VS_Code_Insiders-Install-24bfa5?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fdotnet-wpf.instructions.md) | .NET WPF component and application patterns |
| [draw.io Diagram Standards](../instructions/draw-io.instructions.md)<br />[![Install in VS Code](https://img.shields.io/badge/VS_Code-Install-0098FF?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fdraw-io.instructions.md)<br />[![Install in VS Code Insiders](https://img.shields.io/badge/VS_Code_Insiders-Install-24bfa5?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fdraw-io.instructions.md) | Use when creating, editing, or reviewing draw.io diagrams and mxGraph XML in .drawio, .drawio.svg, or .drawio.png files. |
| [EF Core and async safety (ASP.NET Core)](../instructions/ef-core-async-safety.instructions.md)<br />[![Install in VS Code](https://img.shields.io/badge/VS_Code-Install-0098FF?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fef-core-async-safety.instructions.md)<br />[![Install in VS Code Insiders](https://img.shields.io/badge/VS_Code_Insiders-Install-24bfa5?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fef-core-async-safety.instructions.md) | EF Core and async safety for ASP.NET Core: no sync-over-async, no N+1, AsNoTracking, pagination, DTO projection |
| [Exclude Prompt Data](../instructions/exclude-prompt-data.instructions.md)<br />[![Install in VS Code](https://img.shields.io/badge/VS_Code-Install-0098FF?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fexclude-prompt-data.instructions.md)<br />[![Install in VS Code Insiders](https://img.shields.io/badge/VS_Code_Insiders-Install-24bfa5?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fexclude-prompt-data.instructions.md) | Write only the resulting content into files. Never echo prompt instructions, rationale, or meta-commentary into documentation, comments, or code being produced from a prompt. |
| [Fedora Administration Guidelines](../instructions/fedora-linux.instructions.md)<br />[![Install in VS Code](https://img.shields.io/badge/VS_Code-Install-0098FF?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Ffedora-linux.instructions.md)<br />[![Install in VS Code Insiders](https://img.shields.io/badge/VS_Code_Insiders-Install-24bfa5?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Ffedora-linux.instructions.md) | Guidance for Fedora (Red Hat family) systems, dnf workflows, SELinux, and modern systemd practices. |
| [Genaiscript](../instructions/genaiscript.instructions.md)<br />[![Install in VS Code](https://img.shields.io/badge/VS_Code-Install-0098FF?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgenaiscript.instructions.md)<br />[![Install in VS Code Insiders](https://img.shields.io/badge/VS_Code_Insiders-Install-24bfa5?style=flat-square&logo=visualstudiocode&logoColor=white)](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgenaiscript.instructions.md) | AI-powered script generation guidelines |
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41 changes: 41 additions & 0 deletions instructions/ef-core-async-safety.instructions.md
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---
description: 'EF Core and async safety for ASP.NET Core: no sync-over-async, no N+1, AsNoTracking, pagination, DTO projection'
applyTo: '**/*.cs'
---

# EF Core and async safety (ASP.NET Core)

Frontier C# models still copy JavaScript-shaped patterns: `.Result` on tasks, returning tracked entities from controllers, and N+1 reads. These instructions exist because generic C# guidance does not pin those failures.

Target .NET 8+ / C# 12+. Assume nullable enabled.

## Async I/O

- Async I/O methods return `Task` / `Task<T>` and are suffixed `Async`. Use `ValueTask<T>` only on hot paths that often complete synchronously.
- Never `.Result`, `.Wait()`, or `.GetAwaiter().GetResult()` in application code. Those block a thread and can deadlock.
- No `async void` except real event handlers. Exceptions from `async void` cannot be awaited.
- Flow `CancellationToken cancellationToken = default` as the last parameter through EF Core, `HttpClient`, streams, and delays.
- Do not wrap synchronous I/O in `Task.Run` and call it async.

## EF Core reads

- Use `AsNoTracking()` on read-only queries. Change tracking is only for entities you will `SaveChangesAsync`.
- Prevent N+1: `Include` / `ThenInclude`, or project with `Select`. Prefer projection for read models.
- Do not enable lazy-loading proxies in web apps. They hide N+1 during serialization.
- Paginate unbounded queries (`.Skip().Take()` or keyset). Never materialize a whole table.
- Use `AnyAsync(...)` for existence, not `CountAsync() > 0`.
- Do not combine `Include` with a `Select` projection — pick one.
- Consider `AsSplitQuery()` for multiple collection `Include`s.
- Use async EF APIs and pass `CancellationToken`.

## HTTP boundary

- Controllers are thin: bind, dispatch, map. No business logic and no direct EF in the controller if a service exists.
- Bind request DTOs. Never bind a domain entity (overposting).
- Return response DTOs, not entities.
- `201 Created` with `Location` for creates; `404` for missing; validation failures as `ProblemDetails`.

## Logging

- Use `ILogger<T>` with message templates, not string interpolation.
- Never log secrets or unnecessary PII. Never expose full exception messages to end users.