C#•17mo ago

❔ ASP.NET Core Environment Variables in Dependency Injection

Hello, I have a (probably) slightly dumb question. What's the correct/recommended way to inject an environment variable (like from docker-compose or similar) into a service class in ASP.NET Core? Googling somehow always points me toward "multiple environments" such as test/staging/prod, but that's not what I'm looking for. My hunch is that I'm supposed to do it in Program.cs when setting up DI, somehow. In Spring I might do something like this to inject MY_ENV_VAR as a String into MyService

@Service
class MyService(@Value("${MY_ENV_VAR}") val myEnvVar: String) { ... }

@Service
class MyService(@Value("${MY_ENV_VAR}") val myEnvVar: String) { ... }

11 Replies

mindhardt•17mo ago

I guess you are heading in the wrong direction You need it as a configuration?

phaseshift•17mo ago

Anything in environment can be read through the IConfiguration

mindhardt•17mo ago

Then you would need Microsoft.Extensions.Configuration And you can inhect either a strongly-typed binded Options object or directly IConfiguration

phaseshift•17mo ago

IOptions, yes

mindhardt•17mo ago

Thx for correcting blobthumbsup

CottonOP•17mo ago

Yeah, I ended up with something like this builder.Services.Configure<XsdPackageServiceOptions>(builder.Configuration.GetSection("XsdPackageServiceOptions")); Which is then defined in appsettings.Development.json although I haven't yet tested if actual OS environment variables would affect this at all

mindhardt•17mo ago

Depends on your configuration setup, if you do something like .AddJsonFile().AddEnvironmentVariables() or use default host builder then you are probably fine You can add env vars in your IDE to test things

Unknown User•16mo ago

Message Not Public

MODiX•16mo ago

appsettings.json:

{
  "My": {
    "Foo": {
      "Kix": 5
    }
  }
}

{
  "My": {
    "Foo": {
      "Kix": 5
    }
  }
}

src/Foo/FooOptions.cs:

public class FooOptions
{
  public const string SectionName = "My:Foo";

  public string Bar {get;set;} = "default value for bar";
  public int Kix {get;set;} = -1;
  public DateTime? Pouet {get;set;} = default;
}

public class FooOptions
{
  public const string SectionName = "My:Foo";

  public string Bar {get;set;} = "default value for bar";
  public int Kix {get;set;} = -1;
  public DateTime? Pouet {get;set;} = default;
}

src/Foo/FooServiceCollectionExtensions.cs:

namespace Microsoft.Extensions.DependencyInjection; // <==== recommanded for service.Add so that you don't clutter Startup file

public class FooServiceCollectionExtensions
{
  public static IServiceCollection AddFoo(this IServiceCollection services) =>
    services
      .AddOptions<FooOptions>()
      .BindConfiguration(FooOptions.SectionName)
      .Validate(options => options.Kix >= 0, $"The configuration key '{FooOptions.SectionName}:{nameof(Kix)}' cannot be negative")
      ;

  public static IServiceCollection AddFoo(this IServiceCollection services, Action<FooOptions> configure) =>
    services
      .AddFoo()
      .Configure(configure);

namespace Microsoft.Extensions.DependencyInjection; // <==== recommanded for service.Add so that you don't clutter Startup file

public class FooServiceCollectionExtensions
{
  public static IServiceCollection AddFoo(this IServiceCollection services) =>
    services
      .AddOptions<FooOptions>()
      .BindConfiguration(FooOptions.SectionName)
      .Validate(options => options.Kix >= 0, $"The configuration key '{FooOptions.SectionName}:{nameof(Kix)}' cannot be negative")
      ;

  public static IServiceCollection AddFoo(this IServiceCollection services, Action<FooOptions> configure) =>
    services
      .AddFoo()
      .Configure(configure);

Program.cs / Startup.cs:

services.AddFoo();
// or
services.AddFoo(fooOptions => fooOptions.Kix = 12);

services.AddFoo();
// or
services.AddFoo(fooOptions => fooOptions.Kix = 12);

Bar.cs:

public class Bar
{
  private readonly FooOptions _fooOptions;

  // .Value in ctor is fine only if it's always ever a non-changing value (no reload and/or no scoped resolution)
  public Bar(IOptions<FooOptions> fooOptions)
    => _fooOptions = fooOptions.Value;
}

public class Bar
{
  private readonly FooOptions _fooOptions;

  // .Value in ctor is fine only if it's always ever a non-changing value (no reload and/or no scoped resolution)
  public Bar(IOptions<FooOptions> fooOptions)
    => _fooOptions = fooOptions.Value;
}

Unknown User•16mo ago

Message Not Public

Accord•16mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ ASP.NET Core Environment Variables in Dependency Injection