public static void Main(string[] args)
{
// use a JSON configuration file to specify whether the output should to to the console or to the DB.
var builder = new ConfigurationBuilder()
.SetBasePath(Directory.GetCurrentDirectory())
.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
IConfigurationRoot configuration = builder.Build();
var outputLocation = configuration.GetSection("AppSettings:output_location");
// Configure the dependency injection based on the setting in the config file.
// There's only one HelloWorldService, but the "writer" object is injected into the
// constructor using DI magic.
var serviceProvider = new ServiceCollection()
.AddTransient <IHelloWorldWriter>(s => {
IHelloWorldWriter writer;
if (outputLocation.Value == "console") //constants might be nice here, but this is just for pretend.
{
writer = new HelloWorldConsoleWriter();
}
else if (outputLocation.Value == "sql")
{
writer = new HelloWorldSqlWriter();
}
else
{
throw new ApplicationException("Undefined output type");
}
return(writer);
})
.AddTransient <IHelloWorldService, HelloWorldService>()
.BuildServiceProvider();
// if the configuration file is changed to output_location = "sql", a NotImplementedException is thrown
var helloWorld = serviceProvider.GetService <IHelloWorldService>();
helloWorld.WriteHelloWorld();
}
public void HelloWorldTest_DoesSQLThrowError()
{
var sqlWriter = new HelloWorldSqlWriter();
Assert.ThrowsException <NotImplementedException>(() => sqlWriter.WriteHelloWorld());
}
