WebAPI: Retrieve GET parameter from Controller Constructor

Question

Every call to my WebAPI may (or may not) contain the GET parameter

/api/SomeControllerFunction?loglevel=(someint)

From the function inside the controller I can initialize a LogCollector:

[HttpGet] 
SomeControllerFunction(int loglevel = 0)
{
    LogCollector logger = new LogCollector(loglevel)
}

To not repeat myself too often, I want to hide this in the class hierarchy by adding it into the constructor of a BaseController, from which all my controllers shall inherit:

public class BaseController: ApiController
{
    internal LogCollector Logger
    BaseController()
    {
        Logger = new LogCollector(loglevel);
    }

But how can I access a GET parameter from the constructor?

Igor · Accepted Answer · 2016-04-07 12:57:59Z

Instead of using the constructor you could inject the LogCollector directly into the method. If you did want to use the constructor you should use a Di / IoC framework as that would be more appropriate.

In the example below you can use a custom ActionFilterAttribute instance which injects the Logger based the incoming (optional) log level. The log level is then defined in the route using a RouteAttribute on the action. The RouteAttribute also defines a default value for the log level so it is not required when calling that action.

LogInjectorFilterAttribute.cs

public class LogInjectorFilterAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(HttpActionContext actionContext)
    {
        const string key = "loglevel";
        if(actionContext.ControllerContext.RouteData.Values.ContainsKey(key))
        {
            var loglevel = int.Parse(actionContext.ControllerContext.RouteData.Values[key].ToString());
            LogCollector logger = new LogCollector(loglevel);
            actionContext.ActionArguments["logger"] = logger;
        }
        base.OnActionExecuting(actionContext);
    }
}

HomeController.cs

[HttpGet]
[Route("api/Home/Get/{loglevel:int=1}")]
[LogInjectorFilter]
public IHttpActionResult Get(LogCollector logger)
{
}

Kevin Gosse · Accepted Answer · 2016-04-07 11:16:35Z

4

The constructor is invoked too early, you can't access the parameters from there. However, you can override the Initialize method and retrieve the GET parameters from the context:

protected override void Initialize(HttpControllerContext controllerContext)
{
    foreach (var parameter in controllerContext.Request.GetQueryNameValuePairs())
    {
        Debug.WriteLine(string.Format("{0} = {1}", parameter.Key, parameter.Value));
    }

    base.Initialize(controllerContext);
}

edited Apr 7, 2016 at 11:16

answered Apr 7, 2016 at 11:08

Kevin Gosse

39.1k4 gold badges83 silver badges98 bronze badges

Collectives™ on Stack Overflow

WebAPI: Retrieve GET parameter from Controller Constructor

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related