This package adds variable substitution configuration provider implementation for Microsoft.Extensions.Configuration.
dotnet add package Workleap.Extensions.Configuration.Substitution
// Example for an ASP.NET Core web application
var builder = WebApplication.CreateBuilder(args);
// Setup your configuration
builder.Configuration.AddJsonFile("appsettings.json");
builder.Configuration.AddEnvironmentVariables();
builder.Configuration.AddSubstitution(); // <-- Add this after other configuration providers
You can reference configuration values inside other configuration values by enclosing the referenced configuration key like this: ${ReferencedConfigurationKey}
.
Consider this appsettings.json
:
{
"Credentials": {
"Username": "alice1",
"Password": "P@ssw0rd"
},
"ConnectionString": "usr=${Credentials:Username};pwd=${Credentials:Password}"
}
Evaluating the configuration value ConnectionString
would return usr=alice1;pwd=P@ssw0rd
.
This also works if you're using multiple configuration providers. For instance, one could have the Credentials:Password
configuration value provided by a secret from Azure Key Vault and this value would have been injected into the ConnectionString
value too.
It also works with arrays:
{
"Credentials": [ "alice1", "P@ssw0rd" ],
"ConnectionString": "usr=${Credentials:0};pwd=${Credentials:1}"
}
Again, you're not limited to JSON file providers, you could use substitution with any configuration providers. It was easier to use JSON files in these examples.
You might not want a specific value to be substituted. In that case, escape it using double curly braces:
{
"Foo": "foo",
"Bar": "${{Foo}}"
}
Evaluating the configuration value Bar
would return ${Foo}
.
You can encounter two kinds of exceptions if your configuration is incorrect:
UnresolvedConfigurationKeyException
, if you're trying to substitute a configuration value that is undefined (i.e. the key does not exist).RecursiveConfigurationKeyException
, if you have many configuration values that reference each other in a recursive manner, no matter how deep the recursion is. The exception will give you details about the recursive path.
UnresolvedConfigurationKeyException
can also be triggered sooner than later by using AddSubstitution(eagerValidation: true)
. Using eagerValidation
with value true
(default is false
) instructs the library to check for undefined values in all the existing configuration values once, instead of checking for a particular value. This happens as soon as any configuration value is loaded.
When using .NET's IConfigurationBuilder, the order of configuration providers matters . Any configuration provider added after AddSubstitution()
would not benefit from the substitution process.
Copyright © 2022, Workleap. This code is licensed under the Apache License, Version 2.0. You may obtain a copy of this license at https://github.com/gsoft-inc/gsoft-license/blob/master/LICENSE.