mwyrebski

On domain logic in microservices

A bunch of notes and observations on working and designing microservices. There are not many assumptions in the text except the perspective of functional programming (F# in this case).

Commands

Commands trigger workflows.
Workflows are the keys of business logic. They glue together I/O reads with functions that manipulate the domain objects on which I/O writes are performed afterwards.
- The reason they can accept other functions (dependencies) means they can use mocked domain types.

Domain types should be strongly typed. Raw strings, bools, or ints should prohibited. DateTime can be too vague in some cases when domain logic only allows dates in the future.

Results multimapping a.k.a master-detail in F#

Let's consider how we can query for the relational data given by these sample types:

Company
- Id
- Name
- Country

Get versions of NuGet packages across all repositories using ripgrep.

Switch to the directory with the projects

cd ~/projects_dir

Pull changes for all repositories

find -name .git -type d -prune | xargs -t -I {} git -C {}/.. pull

	//
	// Example of enumerating through Cases of Discriminated Unions.
	//

	type Rgb =
	\| R
	\| G
	\| B

	let colorText c =

	//
	// Example of using enums and enumerating through their values.
	//

	type RgbEnum =
	\| R = 0
	\| G = 1
	\| B = 2

	let colorText e =

	module Seq =

	/// Skips given count from source or returns empty sequence if skip is beyond the limits.
	let safeSkip count source =
	source
	\|> Seq.indexed
	\|> Seq.skipWhile (fun (i, _) -> i < count)
	\|> Seq.map snd

	/// Takes given count from source or returns empty sequence. An alias for the `truncate`.

	<Project Sdk="Microsoft.NET.Sdk">

	<PropertyGroup>
	<TargetFramework>netcoreapp2.2</TargetFramework>
	</PropertyGroup>

	<ItemGroup>
	<PackageReference Include="Microsoft.Extensions.Http.Polly" Version="2.2.0" />
	</ItemGroup>

	// Short demonstration of sequences validation in F#.

	// Sequences, unlike Lists allow null values. Assuming that valid input is a
	// non-empty collection, we have to validate against nulls when using
	// sequences as inputs (assuming nulls can be provided to our functions).

	// Let's assume each function returns Result type which can be either
	// Error with "Invalid input" message or Ok with processed values as list.

	// ------------------------------------------------------------

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	"description": "Quick Notes on Windows",
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	"license": {
	"identifier": "Freeware",
	"url": "https://resoph.com/ResophNotes/Terms_of_Use.html"
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