Dependency Injection in CLI Main, object is null

Question

In my CLI Main I need a object of my MonDbBusinessComponent class. I wrote the code below, but my object is still null. What's wrong? How to do it right?

public static IMonDbBusinessComponent monDbBusinessComponent { get; set; }
static void Main(string[] args)
{
    var collection = new ServiceCollection();
    collection.AddScoped<IMonDbRepository, MonDbRepository>();
    ServiceProvider appServiceProvider = GetServiceProvider();
    monDbBusinessComponent = appServiceProvider.GetService<IMonDbBusinessComponent>();

It's hard to tell, because your example doesn't show what GetServiceProvider() is doing. It's likely null because IMonDbBusinessComponent isn't in the service collection. — Nate Barbettini
– Nate Barbettini, Commented Sep 12, 2019 at 20:07
Is your program a console app? You may not need dependency injection with a service collection at all. Can you simply do new MonDbBusinessComponent(new MonDbRepository? — Nate Barbettini
– Nate Barbettini, Commented Sep 12, 2019 at 20:09

Paul Lorica · Accepted Answer · 2019-09-12 20:17:31Z

1

you never registered your IMonDbBusinessComponent.

collection.AddScoped<IMonDbBusinessComponent, MonDbBusinessComponent>();

answered Sep 12, 2019 at 20:17

Paul Lorica

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1 Comment

Frank Mehlhop Over a year ago

Thats right. I register a other class.(Repository instead of BusinessComponent.) But now after adding BusinessComponent my object is still null.

Frank Mehlhop · Accepted Answer · 2019-09-12 20:48:50Z

I'm sorry, it was not possible to see in my published coded. The BusinessComponent uses Repository and first I needed to register the Repository with it's arguments and then register the BusinessComponent. Also at the BusinessComonent I needed to use the Interface instead of the class.

public MonDbBusinessComponent(IMonDbRepository monDbRepository){...}

collection.AddScoped<IMonDbRepository>(ServiceProvider =>
{
    string createMetaDataRecordFunctionName = Configurations.Get(LocalConfiguration, "CreateMetaDataRecordFunctionName");
    string conDbDataRecordFunctionName = Configurations.Get(LocalConfiguration, "ConDbDataRecordFunctionName");
    return new MonDbRepository(metaDataConnection, createMetaDataRecordFunctionName, conDbDataRecordFunctionName);
});
collection.AddScoped<IMonDbBusinessComponent, MonDbBusinessComponent>();

Thanks for all support!

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