Dependency Injection Setup for .NET Console Application

This post describes the foundational steps to configure the Microsoft dependency injection container for a C# console application.

Nuget

Once you have a basic console application, you need to install the following Nuget packages:

Microsoft.Extensions.Hosting
Microsoft.Extensions.DependencyInjection

Setting up the Host

The following code is the barest basics for configuring the Microsoft.Extensions.Hosting.Host.

  using Microsoft.Extensions.DependencyInjection;
  using Microsoft.Extensions.Hosting;
  
  IHost host = Host.CreateDefaultBuilder(args)
    .Build();

  // do stuff

  await host.RunAsync();

The Host static class has a single method CreateDefaultBuilder.

The CreateDefaultBuilder method is interesting as it does a lot of really helpful stuff for us. Per the documentation, it:

Sets the ContentRootPath to the result of GetCurrentDirectory().
Loads host IConfiguration from “DOTNET_” prefixed environment variables.
Loads app IConfiguration from ‘appsettings.json’ and ‘appsettings.[EnvironmentName].json’.
Loads app IConfiguration from User Secrets when EnvironmentName is ‘Development’ using the entry assembly.
Loads app IConfiguration from environment variables.
Configures the ILoggerFactory to log to the console, debug, and event source output.
Enables scope validation on the dependency injection container when EnvironmentName is ‘Development’.

That’s a lot of useful stuff that we don’t have to do by hand. It means we can do things like:

store and retrieve configuration from many sources, including appsettings.json and any of the environment-specific variants (eg. appsettings.Development.json)
provide configuration via the command line that will over-ride an equivalent configuration item stored in appsettings.json
start adding services into the dependency injection container

Finally, we need to call Build(). Without this, we will create an instance of IHostBuilder. Build() belongs to the IHostBuilder interface and we use it to create an instance of IHost.

Documentation

Microsoft provides documentation for the dependency injection container here.

Injecting services

From here, things are pretty much identical to configuring the DI container in a WebAPI app.

Chaining on the ConfigureServices() method allows you to configure the dependency injection container. In the sample below, I am injecting two services.

services.AddSingleton<IDataAccess, DataAccess>();
- This is setting up a singleton for the IDataAccess contract to resolve to the DataAccess type.
services.AddSingleton<DataAccess.CreateDbConnection>((serviceProvider) =>{});
- This one is a little bit interesting. DataAccess.CreateDbConnection is a delegate type. In the code contained inside the parens, I am configuring the IDbConnection type that Dapper is using depending on the value in the ASPNET_ENVIRONMENT environment variable.
- I found this blog post from Christian Findlay helpful in building my understanding of this.

  var host = Host.CreateDefaultBuilder(args).ConfigureServices(
      services =>
      {
          services.AddSingleton<IDataAccess, DataAccess>();
          services.AddSingleton<DataAccess.CreateDbConnection>((serviceProvider) =>
          {
              var config = serviceProvider.GetRequiredService<IConfiguration>();
              var aspnetEnvironment = config.GetSection("ASPNET_ENVIRONMENT").Value;
              Console.WriteLine($"ASPNET_ENVIRONMENT: {aspnetEnvironment}");

              return aspnetEnvironment switch
              {
                  "Development" => SqlConnectionProvider.CreateDbConnection,
                  "Test" => SqliteConnectionProvider.CreateInMemoryDbConnection,
                  _ => SqliteConnectionProvider.CreateDbConnection
              };
          });
      }
  ).Build();

Want to see it in use?

I have created a sample console application that is using the Microsoft dependency injection container. Here is the direct link to the Program.cs file.

This demo application uses Dapper to access a database. There are a couple of issues right now relating to the creation of the in memory SQLite DB but otherwise it illustrates of using Dapper and configuring the database connection using dependency injection.

Mike Hansford