CommandQuery<!-- omit in toc -->

Content<!-- omit in toc -->

• Introduction
• Packages
  • CommandQuery ⚙️
  • CommandQuery.AspNetCore 🌐
  • CommandQuery.AWSLambda ⚡
  • CommandQuery.AzureFunctions ⚡
  • CommandQuery.GoogleCloudFunctions ⚡
  • CommandQuery.Client 🧰
• Upgrading
• Acknowledgements

Introduction

Command Query Separation (CQS) for .NET and C#

• Build services that separate the responsibility of commands and queries
• Focus on implementing the handlers for commands and queries
• Create APIs with less boilerplate code

Available for:

🌐 ASP.NET Core
⚡ AWS Lambda
⚡ Azure Functions
⚡ Google Cloud Functions

Command Query Separation?

Queries: Return a result and do not change the observable state of the system (are free of side effects).

Commands: Change the state of a system but do not return a value.

— <cite>Martin Fowler</cite>

In other words:

• Commands
  • Writes (create, update, delete) data
• Queries
  • Reads and returns data

The traditional approach that commands do not return a value is a bit inconvenient.

CommandQuery has a pragmatic take and supports both commands with and without result 👍

Packages

CommandQuery ⚙️

Command Query Separation for .NET

• 📃 README: CommandQuery.md
• 💁 Samples:
  • CommandQuery.Sample.Contracts
  • CommandQuery.Sample.Handlers

CommandQuery.AspNetCore 🌐

Command Query Separation for ASP.NET Core

• 📃 README: CommandQuery.AspNetCore.md
• 💁 Samples:
  • CommandQuery.Sample.AspNetCore
  • CommandQuery.Sample.AspNetCore.Tests

CommandQuery.AWSLambda ⚡

Command Query Separation for AWS Lambda

• 📃 README: CommandQuery.AWSLambda.md
• 💁 Samples:
  • CommandQuery.Sample.AWSLambda
  • CommandQuery.Sample.AWSLambda.Tests

CommandQuery.AzureFunctions ⚡

Command Query Separation for Azure Functions

• 📃 README: CommandQuery.AzureFunctions.md
• 💁 Samples:
  • CommandQuery.Sample.AzureFunctions
  • CommandQuery.Sample.AzureFunctions.Tests

CommandQuery.GoogleCloudFunctions ⚡

Command Query Separation for Google Cloud Functions

• 📃 README: CommandQuery.GoogleCloudFunctions.md
• 💁 Samples:
  • CommandQuery.Sample.GoogleCloudFunctions
  • CommandQuery.Sample.GoogleCloudFunctions.Tests

CommandQuery.Client 🧰

Clients for CommandQuery APIs

• 📃 README: CommandQuery.Client.md
• 💁 Samples:
  • CommandQuery.Sample.Client

Upgrading

⬆️ Upgrading from version 3.0.0 to 4.0.0

Upgrade AspNetCore:

• Upgrade the project target framework to net8.0

Upgrade AWSLambda:

• Upgrade the project target framework to net8.0

Upgrade AzureFunctions:

• Upgrade the project target framework to net8.0
• Remove the logger argument from HandleAsync
• Consider to use the HttpRequest versions of HandleAsync

Upgrade GoogleCloudFunctions:

• Upgrade the project target framework to net8.0
• Remove the logger argument from HandleAsync

Acknowledgements

Inspired by Steven van Deursen blog posts:

• Meanwhile... on the command side of my architecture
• Meanwhile... on the query side of my architecture