FSharp.Appsettings - F#

Minimalistic environment-sensitive appsettings.json loader.

Usage

Define FSHARP_ENVIRONMENT as an environment variable. For development this will normally be done by creating a launchSettings.json file:

{
	"$schema": "https://json.schemastore.org/launchsettings.json",
	"profiles": {
		"Development": {
			"commandName": "Project",
			"environmentVariables": {
				"FSHARP_ENVIRONMENT": "Development"
			}
		}
	}
}

You can then run this code to load one or two appsettings.json files with this code:

open FSharp.Appsettings

let appsettings = Appsettings.Load ()

// Deserialize to type
open System.Text.Json

let required = appsettings.Deserialize<RequiredConfig>()

appsettings.json will always be loaded, while appsettings.{FSHARP_ENVIRONMENT}.json will be loaded if FSHARP_ENVIRONMENT is defined as an environment variable.
Properties from appsettings.json will be overwritten by the environment specific appsettings.
Arrays will be added together if a value does not already exist in the array.

Example

// appsettings.json
{
	"Env": "Root",
	"CORS": {
		"AllowedOrigins": [
			"https://localhost:3000", "https://fsharp.org"
		]
	},
	"Logging": {
		"LogLevel": {
			"Default": "Debug",
			"System": "Information",
			"Microsoft": "Information",
			"Test": "Critical"
		}
	},
	"OnlyRoot": "Root"
}

// appsettings.Development.json (FSHARP_ENVIRONMENT=Development)
{
	"Env": "Development",
	"CORS": {
		"AllowedOrigins": [
			"https://localhost:3000"
		]
	},
	"Logging": {
		"LogLevel": {
			"Default": "Debug",
			"System": "Information",
			"Microsoft": "Information"
		}
	},
	"OnlyDev": "Dev"
}

// Resulting object after Appsettings.load ()
{
	"Env": "Development",
	"CORS": {
		"AllowedOrigins": [
			"https://localhost:3000", "https://fsharp.org"
		]
	},
	"Logging": {
		"LogLevel": {
			"Default": "Debug",
			"System": "Information",
			"Microsoft": "Information",
			"Test": "Critical"
		}
	},
	"OnlyDev": "Dev",
	"OnlyRoot": "Root"
}

Note: This NuGet does not support defining secrets by defining <UserSecretsId> in the .csproj file.
Instead it detects appsettings{.FSHARP_ENVIRONMENT?}.local.json that you can (should) add to .gitignore.

Order of Priority

1. appsettings.{FSHARP_ENVIRONMENT}.local.json
2. appsettings.local.json
3. appsettings.{FSHARP_ENVIRONMENT}.json
4. appsettings.json

Building

The appsettings.json files must be copied over to output directory. This is achieved by adding the following to your .fsproj.

<ItemGroup>
	<Content Include="appsettings*.json">
		<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
		<CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
	</Content>
</ItemGroup>

Merge rules

Describes what happens when a field from appsettings A encounters a field with the same name from appsettings B

1. Value A - Value B: Value B overwrites value A
2. Object A - Object B: Recursion
3. Array A - Array B: Items from array A are added to array B if not already present
4. Value A - Object B: Object B replaces value A
5. Value A - Array B: Array B replaces value A
6. Object A - Value B: Value B replaces Object A
7. Object A - Array B: Array B replaces Object A
8. Array A - Value B: Value B replaces Array A
9. Array A - Object B: Object B replaces Array A

Committing

Important to run this before committing (assuming you have GPG key set up)

git config commit.gpgsign true