Develop Reference

C# Injecting Specific Item from appSettings.json at runtime

How can I inject a specific setting (of possibly many) from an array appSettings.json in a C# .NET Core Web API, based on a runtime input value?
appSettings.json:
{
"SettingProfiles": [
{
"Name": "Profile1",
"SettingA": "SettingAValue1",
"SettingB": "SettingBValue1"
},
{
"Name": "Profile2",
"SettingA": "SettingAValue2",
"SettingB": "SettingBValue2"
}
...
}
Settings Classes:
public class Settings {
public List<SettingsProfile> SettingsProfiles { get; set; }
}
public class SettingsProfile {
public string Name { get; set; };
public string SettingA { get; set; };
public string SettingB { get; set; };
}
Service class:
public class MyService : IMyService {
private readonly SettingsProfile _Profile;
public MyService(SettingsProfile profile) {
_Profile = profile;
}
public void DoStuff() {
Console.WriteLine($"Setting A: {_SettingsProfile.SettingA}, Setting B: {_SettingsProfile.SettingB}")
}
}
The user will enter the setting name they want to apply. I am unsure how to do this if the service is configured in Startup.cs, at which point I don't yet have the setting to use.
I am understanding that "newing" the service would be bad practice, although that's the only way I can figure out how to make it work:
public class MyController {
private readonly Settings _Settings;
public MyController(Settings settings) {
_Settings = settings;
}
public IActionResult DoStuff(profileName) {
SettingsProfile profile = _Settings.Where(profile => profile.Name == profileName);
MyService service = new Service(profile);
}
}
I'm obviously missing something, but I've been watching YouTube videos on Dependency Injections and reading StackOverflow until my eyes bleed, and haven't figured it out yet. Can someone help me with a pattern that I should be following?

This is how I think it should work.
It will be a lot cleaner if you use another pattern: Factory.
interface ISettingServiceFactory{
MyService GetService(string profileName);
}
class SettingServiceFactory: ISettingServiceFactory
{
MyService GetService(string profileName){
}
}
Now you can implement GetService in two ways.
The first one is by creating new as you did in the controller and is not that bad as this is the purpose of the factory. In this way you kind of move that logic somewhere else.
A second one would be a bit uglier but something like this
interface ISettingServiceFactory{
MyService GetService(string profileName);
void SetCurrentProfile(SettingsProfile profile);
}
class SettingServiceFactory: ISettingServiceFactory
{
private IServiceProvider _serviceProvider;
private Settings _Settings;
public SettingServiceFactory(IServiceProvider serviceProvider,Settings settings){
_serviceProvider = serviceProvider;
_Settings = settings;
}
MyService GetService(string profileName){
var service = _serviceProvider.GetRequiredService<MyService>();
var profile = _Settings.Where(profile => profile.Name == profileName);
service.SetCurrentProfile(profile);
return service;
}
}
This second approach would be useful only if the implementation of MyService has a lot of other dependencies by itself and if you want to avoid new at any cost.
In both cases you will inject the factory in the controller
public MyController(ISettingServiceFactory settingServiceFactory) {
_settingServiceFactory= settingServiceFactory;
}
public IActionResult DoStuff(profileName) {
MyService service = _settingServiceFactory.GetService(profileName)
}

.NET Core Dependency Injection how to handle multiple objects

As the title says I have a .NET Core application that I am trying to convert over to and take advantage of the built in Microsoft Dependency Injection.
I have an object and a base class for the object, call it CommunicationBase and Communicator. When my app starts up and reads the configuration file, I can have N number of objects to instantiate.
Previously, before switching to Dependency Injection, somewhere in my startup routine, where I read the configuration file, I would have a List<CommunicationBase> variable that I would instantiate and add Communicator objects to and at the same time, set some of the base properties, which changed based on how many were in my configuration and each ones properties in config.
How would I achieve this with DI?
I understand that in my services, I would register the type so it can be injected into other class constructors.
For example, services.AddTransient<CommunicationBase, Communicator>(); but as I understand it, this just registers the types with DI. I can inject it into a class and have a random instance of one of them.
How would I then have N number of instances and be able to set properties of each one as I create the instance?
Or, is this a scenario where DI is not necessary or won't work and I need to just do it the way I was doing it before?
Thanks!

I would slightly modify approach shown here. So I would define some enum that would then be used to decide what instance to return.
Sample classes setup and the enum:
public enum CommuniationType
{
False, True, Other,
}
public abstract class CommunicationBase
{
public CommunicationBase(CommuniationType communiationType)
{
CommuniationType = communiationType;
}
public bool IsConnected { get; set; }
public CommuniationType CommuniationType { get; protected set; }
}
public class Communicator : CommunicationBase
{
public Communicator(CommuniationType communiationType) : base(communiationType) { }
}
Now, in the place where you have access to service collection (e.g. in ASP.NET the place would be Stratup.RegisterServices method) you define your objects of concrete class and register them, as in the sample code below (at the bottom, there are also test classes using CommunicationBase object for testing puproses):
public class Program
{
static void Main(string[] args)
{
var serviceCollection = new ServiceCollection();
SetupNObjects(serviceCollection);
serviceCollection.AddTransient<CommunicationBaseServiceResolver>(serviceProvider => communicationType =>
{
var implementations = serviceProvider.GetServices<CommunicationBase>();
return implementations.First(x => x.CommuniationType == communicationType);
});
serviceCollection.AddScoped<FalseTestClass>();
serviceCollection.AddScoped<TrueTestClass>();
var serviceProvider = serviceCollection.BuildServiceProvider();
var f = serviceProvider.GetService<FalseTestClass>();
var t = serviceProvider.GetService<TrueTestClass>();
}
// Here you should take care of registering objects, after reading config.
// That would be best place to do that.
static void SetupNObjects(ServiceCollection serviceCollection)
{
var comFalse = new Communicator(CommuniationType.False);
comFalse.IsConnected = false;
var comTrue = new Communicator(CommuniationType.True);
comTrue.IsConnected = true;
serviceCollection.AddScoped<CommunicationBase>((serviceProvider) => comFalse);
serviceCollection.AddScoped<CommunicationBase>((serviceProvider) => comTrue);
}
}
public class FalseTestClass
{
private readonly CommunicationBase communication;
public FalseTestClass(CommunicationBaseServiceResolver resolver)
{
communication = resolver(CommuniationType.False);
}
}
public class TrueTestClass
{
private readonly CommunicationBase communication;
public TrueTestClass(CommunicationBaseServiceResolver resolver)
{
communication = resolver(CommuniationType.True);
}
}

Firstly do you need to has clear the differences between Transient, Scoped, Singleton lifetime. To understand how works with the list of Communicator objects that will be read from your configuration file.
One approuch to resolve your question is
Create an interface ICommunicatorList with one method to get a List, i mean you can envolve the list of communicators.
Create a clase that inherits from ICommunicatorList (for example called CommunicatorList), with a private field for your list of Communicators. On the constructor method set your private field with the list of communicator, o here you can receive like a parameter from the section of the config file to iterate and full your private field.
on this class implement your code to return the list of communicators.
Now, in your startups file you can now create the service
services.AddTransient< ICommunicatorList>(x => new CommunicatorList(parameters));

I would do it the following way.
First you have communicators and settings classes:
namespace WebApiApp
{
public abstract class CommunicationBase
{
public abstract string Communicate();
}
public class Communicator1Settings
{
public string Parameter { get; set; }
}
public class Communicator1 : CommunicationBase
{
private readonly string parameter;
public Communicator1(string parameter)
{
this.parameter = parameter;
}
public override string Communicate()
{
return $"Type: {nameof(Communicator1)}, parameter: {this.parameter}";
}
}
public class Communicator2Settings
{
public string Parameter1 { get; set; }
public string Parameter2 { get; set; }
}
public class Communicator2 : CommunicationBase
{
private readonly string parameter1;
private readonly string parameter2;
public Communicator2(string parameter1, string parameter2)
{
this.parameter1 = parameter1;
this.parameter2 = parameter2;
}
public override string Communicate()
{
return $"Type: {nameof(Communicator1)}, parameter1: {this.parameter1}, parameter2: {this.parameter2}";
}
}
public class CommunicatorsSettings
{
public List<Communicator1Settings> Communicators1 { get; set; }
public List<Communicator2Settings> Communicators2 { get; set; }
}
}
In appsettings.json you have the configuration of communicators:
{
"Logging": {
"LogLevel": {
"Default": "Information",
"Microsoft.AspNetCore": "Warning"
}
},
"AllowedHosts": "*",
"Communicators": {
"Communicators1": [
{
"Parameter": "First communicator1 parameter"
},
{
"Parameter": "Second communicator1 parameter"
}
],
"Communicators2": [
{
"Parameter1": "First communicator2 parameter1",
"Parameter2": "First communicator2 parameter2"
},
{
"Parameter1": "Second communicator2 parameter1",
"Parameter2": "Second communicator2 parameter2"
}
]
}
}
So you have two instances of Communicator1 with different parameters and two instances of Communicator2 with different parameters as well.
Then, you configure the container. The following is the content of program.cs for .net 6:
using WebApiApp;
var builder = WebApplication.CreateBuilder(args);
// Add services to the container.
AddCommunicators();
builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
var app = builder.Build();
// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
app.UseSwagger();
app.UseSwaggerUI();
}
app.UseHttpsRedirection();
app.UseAuthorization();
app.MapControllers();
app.Run();
void AddCommunicators()
{
var settings = new CommunicatorsSettings();
builder.Configuration.Bind("Communicators", settings);
foreach (var communicatorSettings in settings.Communicators1)
{
builder.Services.AddScoped<CommunicationBase>(
_ => new Communicator1(communicatorSettings.Parameter));
}
foreach (var communicatorSettings in settings.Communicators2)
{
builder.Services.AddScoped<CommunicationBase>(
_ => new Communicator2(communicatorSettings.Parameter1, communicatorSettings.Parameter2));
}
}
Now you can inject IEnumerable<CommunicationBase> into your controller:
using Microsoft.AspNetCore.Mvc;
namespace WebApiApp.Controllers
{
[ApiController]
[Route("[controller]")]
public class CommunicatorsController : Controller
{
private readonly IEnumerable<CommunicationBase> communicators;
public CommunicatorsController(IEnumerable<CommunicationBase> communicators)
{
this.communicators = communicators;
}
public IActionResult Get()
{
var result = this.communicators.Select(x => x.Communicate());
return this.Json(result);
}
}
}
This is the result for /communicators web API:
[
"Type: Communicator1, parameter: First communicator1 parameter",
"Type: Communicator1, parameter: Second communicator1 parameter",
"Type: Communicator1, parameter1: First communicator2 parameter1, parameter2: First communicator2 parameter2",
"Type: Communicator1, parameter1: Second communicator2 parameter1, parameter2: Second communicator2 parameter2"
]

.NET Core Configuration is forcing me to DependencyInjection

I want to read appsettings.json non-controller class.Consider has a DatabaseUtil and contain a static connect() method. I need to connectionString for connection and i'm getting this from appsettings.json.This operation piece of cake in the startup.cs:)
Like this:
Configuration.GetConnectionString("HangfireDBConn")
Also it can be at the controller side with dependcy injection.But my problem which want to reach appSettings from DatbaseUtil class.
appSettings.json:
"NotifySettings": {
"DbConnection": "abc",
"Email": "abc#domain.com",
"SMTPPort": "5605"
}
Then i created my configuration settings class:
public class NotifySettings
{
public string DbConnection { get; set; }
public string Email { get; set; }
public string SMTPPort { get; set; }
}
And I added dependency for constructor injection to DatabaseUtil class and added IDatabaseUtil
public class DatabaseUtil : IDatabaseUtil
{
private static NotifySettings _NotifySettings;
public DatabaseUtil(IConfiguration _iconfig)
{
_NotifySettings = _iconfig.GetSection("NotifySettings").Get<NotifySettings>();
}
public static String ConnectToDatabase()
{
return "MESSAGE :" + _NotifySettings.DbConnection;
}
}
}
And i added DatabaseUtil to startup.cs
services.AddScoped<IDatabaseUtil, DatabaseUtil>();
and finally i injected IDatabaseUtil to my controller class and i can reach mysettings end of the this work.
Yes i can but not best way!
Let the join my Brain Storming :) ; If i have to inject to IDatabaseUtil every class where i want to use db helper methods.But if i had a static method in this class just it need to this line of code:
DatabaseUtils.connect();
That's feels me like i wrote unnecessary code.
What do you think about my approximation.Which one is best way for this case ?

change
services.AddScoped<IDatabaseUtil, DatabaseUtil>();
to
services.AddSingleton<IDatabaseUtil, DatabaseUtil>();
This way you only have one instance of DatabaseUtil

I'm still not entirely clear, but if the need here is to make values from your Configuration statically available, then copy them from your configuration to a static class during the startup:
public static class GlobalSettings
{
public static string ConnectionString { get; set; }
}
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
public void ConfigureServices(IServiceCollection services)
{
GlobalSettings.ConnectionString = Configuration.GetSection("ConnectionString").Value;
// ...
}
}
If you need to get the config and do the assignment from somewhere else, use the ConfigurationBuilder:
var config = new ConfigurationBuilder()
.AddJsonFile("appsettings.json")
.Build();

using System;
using Microsoft.Extensions.Configuration;
namespace project.Utility
{
public class ConnectionString
{
private IConfigurationRoot _config;
private static ConnectionString _internalInstance;
public static ConnectionString Instance
{
get
{
return _internalInstance;
}
}
public static void Init(IConfigurationRoot config)
{
_internalInstance = new ConnectionString();
_internalInstance._config = config;
}
public String Get(string key)
{
var NotifySettings =
Instance._config.GetSection(key).Get<NotifySettings>();;
return NotifySettings;
}
}
}
// call this above method from any place like controller or class file by below code
// use refernece of the namespace
ConnectionString connectionString = new ConnectionString(); // object creation
NotifySettings settings = connectionString.Get("NotifySettings"); // call with your key value get the settings object
Try this it should work let me know if any issues i can help on that

ASP.NET Core MVC inject per request

I am looking forward to inject RequestContext, per request in .Net Core. inside the service collection.
Someone attempted 8 yrs. ago.
ASP.NET MVC inject per request
public interface IMvcDepency
{
string PathValue { get; set; }
}
public class FakeMvcDepency : IMvcDepency
{
public string PathValue { get; set; }
}
public class MvcDepency : IMvcDepency
{
public string PathValue { get; set; }
public MvcDepency(HttpRequest req)
{
PathValue = req.Path.Value;
}
}
And inject it somewhere in startup, as follows:
services.AddTransient<IMvcDepency, MvcDepency>(x => x.???);
or in OnActionExecuting like below:
public override void OnActionExecuting(ActionExecutingContext actCtx)
{
MvcDepency mvcDepency = actCtx.HttpContext.RequestServices.GetService(typeof(IMvcDepency)) as MvcDepency;
mvcDepency = new MvcDepency(actCtx.HttpContext.Request);
actCtx.HttpContext.RequestServices.AddService(mvcDepency);// AddService method doesn't in exist
}
Current Error:
System.InvalidOperationException: 'Unable to resolve service for type 'Microsoft.AspNetCore.Http.HttpRequest' while attempting to activate 'CAWP.Api.Controllers.MvcDepency'.'

Controllers already have access to the HttpRequest object in each of the methods via the base class. But it is only available once a method is called (for obvious reasons!). If you want to wrap it in your own class then you can do it in the OnActionExecuting override.
You can create a new MvcDepency class in OnActionExecuting and reference it in the code. As controllers are created per request you should be able to use a class variable to store the reference.
public class ValuesController : Controller
{
private IMvcDepency _depency;
public ValuesController()
{
}
public override void OnActionExecuting(ActionExecutingContext context)
{
_depency = new MvcDepency(context.HttpContext.Request);
base.OnActionExecuting(context);
}
// GET api/values
[HttpGet]
public ActionResult<IEnumerable<string>> Get()
{
var path = _depency.PathValue;
return new string[] { "PathValue", path };
}
}
This should result in the MvcDepency class having access to the HttpRequest object.
You should add a factory class for your IMvcDepency interface to avoid the new in OnActionExecuting.

Refactoring class to make it injectable/mockable

I am really struggling to properly refactor my class so I can inject it.
This is the class I am talking about:
internal class OCRService : IDisposable, IOCRService
{
private const TextRecognitionMode RecognitionMode = TextRecognitionMode.Handwritten;
private readonly ComputerVisionClient _client;
public OCRService(string apiKey)
{
_client = new ComputerVisionClient(new ApiKeyServiceClientCredentials(apiKey))
{
Endpoint = "https://westeurope.api.cognitive.microsoft.com"
};
}
public async Task<List<Line>> ExtractTextAsync(byte[] image)
{
//Logic with _client here
}
}
I really don't know where to Initialize the ComputerVisionClient. I am thinking of the following options:
Make ComputerVisionClient a public property which can be set after injecting.
Putting the apikey in a config file and then read it in the constructor.
The problem is that I want to mock this service but when I mock it it still calls the constructor which connects to the ComputerVisionClient.

Depending on the rest of your architecture, you have a few options. The simplest is to inject the ComputerVisionClient (or IComputerVisionClient if you can create one) into the constructor, and mock it in your tests.
public class OCRService : IOCRService, IDisposable
{
public OCRService(IComputerVisionClient client)
{
_client = client;
}
}
If, for some reason, you must create the client in the constructor, you can create a factory and inject that:
internal class ComputerVisionClientFactory : IComputerVisionClientFactory
{
public GetClient(string apiKey)
{
return new ComputerVisionClient(new ApiKeyServiceClientCredentials(apiKey))
{
Endpoint = "https://westeurope.api.cognitive.microsoft.com"
};
}
}
// ...
internal class OCRService : IOCRService, IDisposable
{
public OCRService(string apiKey, IComputerVisionClientFactory clientFactory)
{
_client = clientFactory.GetClient(apiKey);
}
}
As #maccettura suggested, you can also further abstract away the apiKey by creating an IOCRServiceConfiguration that contains the logic for getting the key, and pass that into the constructor for either OCRService or ComputerVisionFactory, depending on your architecture. Naively:
internal class OCRServiceConfiguration : IOCRServiceConfiguration
{
public OCRServiceConfiguration(string apiKey)
{
ApiKey = apiKey;
}
public string ApiKey { get; }
}