Best way to inject instance of DynamoDBContext in .NET Core

Question

Currently working on a web services project for my class and have decided to make a web API using .NET Core and DynamodDB.

I was just curious what the best way to inject the DynamoDBContext is?

I currently am doing it like this:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();

    services.AddDefaultAWSOptions(Configuration.GetAWSOptions());
    services.AddAWSService<IAmazonDynamoDB>();
}

I got this piece of code above from the DynamoDB documentation. I add an instance of IAmazonDynamoDB to the project.

DynamoDBContext context;
public ValuesController(IAmazonDynamoDB context)
{
    this.context = new DynamoDBContext(context);
}

In the controller, I then inject the IAmazonDynamoDB instance, and use that to create an instance of DynamoDBContext.

Is there a way to create an instance of the context in the ConfigureServices method and add it to the project there, or is the way I am doing it currently fine?

Answer 1

Is there a way to create an instance of the context in the ConfigureServices method and add it to the project there, or is the way I am doing it currently fine?

Although your solution will work, it has a drawback. You're not using Dependency Injection for DynamoDBContext and create its instance in controller constructor through new operator. You'll face a problems when it comes to unit testing your code, because you have no way to substitute implementation of DynamoDBContext.

The proper way is to register DynamoDBContext in DI container and let the container itself create an instance when it's required. With such approach IDynamoDBContext gets injected into ValuesController:

public class ValuesController
{
    private readonly IDynamoDBContext context;

    public ValuesController(IDynamoDBContext context)
    {
        this.context = context;
    }

    // ...
}

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();

    services.AddDefaultAWSOptions(Configuration.GetAWSOptions());
    services.AddAWSService<IAmazonDynamoDB>();
    services.AddTransient<IDynamoDBContext, DynamoDBContext>();
}