Let's move on to implementing the action method for getting a single question:

1. Add the following skeleton method:

[HttpGet("{questionId}")]
public ActionResult<QuestionGetSingleResponse> 
  GetQuestion(int questionId)
{
    // TODO - call the data repository to get the question
    // TODO - return HTTP status code 404 if the question isn't     
       found
    // TODO - return question in response with status code 200
}

Note the HttpGet attribute parameter.

In this method, the questionId parameter will be set to whatever comes after the controller root path. So, for the api/questions/3 path, questionId would be set to 3.

Notice that the return type is ActionResult<QuestionGetSingleResponse> rather than just QuestionGetSingleResponse. This is because our action method won't return QuestionGetSingleResponse in all the return paths—there will be a path that will return NotFoundResult when the question can't be found. ActionResult gives us the flexibility to return these different types.

2. Let's call into the repository to get the question:

[HttpGet("{questionId}")]
public ActionResult<QuestionGetSingleResponse> 
  GetQuestion(int questionId)
{
    var question = _dataRepository.GetQuestion(questionId);
    // TODO - return HTTP status code 404 if the question isn't  
       found
    // TODO - return question in response with status code 200
}

3. Next, we can check whether the question has been found and return HTTP status code 404 if it hasn't been found:

[HttpGet("{questionId}")]
public ActionResult<QuestionGetSingleResponse> GetQuestion(int questionId)
{
    var question = _dataRepository.GetQuestion(questionId);
    if (question == null)
    {
        return NotFound();
    }
    // TODO - return question in response with status code 200
}

If the question isn't found, the result from the repository call will be null. So, we check for null and return a call to the NotFound method in ControllerBase, which returns HTTP status code 404.

4. The last implementation step is to return the question that has been found:

[HttpGet("{questionId}")]
public ActionResult<QuestionGetSingleResponse> GetQuestion(int questionId)
{
    var question = _dataRepository.GetQuestion(questionId);
    if (question == null)
    {
        return NotFound();
    }
    return question;
}

5. Let's give this a try by running the app and requesting question 1:

The question is returned as expected.

6. Let's try requesting a question that doesn't exist:

We can get confirmation that a 404 status code is returned by opening the Dev Tools by pressing F12 and looking at the Network panel to see when the request was made.

7. Stop our app running so that we are ready to implement another action method.

We've implemented a range of action methods that handle GET requests. It's time to implement action methods for the other HTTP methods next.