How do I centralize code shared by multiple Web API controllers?

Question

I have close to 10 controllers that currently share the same code. The code is pretty simple, it just checks if a set of data is null and checks if the current user has permission to access the data.

If there is an issue, I throw an HttpResponseException.

The code works when it is sitting in each controller. I have also managed to centralize the code but I think the way I have done it is wrong. I've created a new class which inherits ApiController and then I have the controllers inheriting my new class. This is the only way I could get the HttpResponseExceptions working. Code is as follows:

//New centralized class:

public class AuthorizationClass : ApiController
{   
    private DataModel db = new DataModel();

    public async Task checkUserisValid(int user_id)
    {
        user_list user_list = await db.user_list.FindAsync(user_id);

        if (user_list == null)
        {
            throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.BadRequest,"This user does not exist"));
        }

        int businessID = user_list.business_id;

        var result = checkAccess(User.Identity.Name, businessID);

        if (result.Count <= 0)
        {
            throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.Unauthorized, "You do not have access to modify this business"));
        }
    }

    public static List<user_details> checkAccess(string userName, int id)
    {
        //code which checks if the user is in the right tables
            return checkAccess.ToList();
    }
}

Then in the controller class, I have:

    public class MyController : AuthorizationClass 
{
        public async Task<IHttpActionResult> Postnew_table(int id, new_table new_table)
        {
            await checkUserisValid(id);

        //rest of controller    
            }
}

I tried to do it in different ways but this is the only way I could get it working with HttpResponseException. Is there a better way to do this without inheriting classes or is this the only way to do what I am after?

Thanks.

This isn't Classic ASP. It looks like it might be asp.net mvc — John
– John, Commented Jan 2, 2015 at 0:33
why must this code be in the controller? Why not have a common assembly? But I also don't see anything wrong with it, every controller will inherit from AuthorizationClass? I guess that works. — T McKeown
– T McKeown, Commented Jan 2, 2015 at 0:39
why? maybe you should pass the dbcontext as an argument? make it work. — T McKeown
– T McKeown, Commented Jan 2, 2015 at 0:55

T McKeown · Accepted Answer · 2015-01-02 01:51:37Z

You could just move these 2 methods to some static helper class in a common assembly, you mention that Request is an instance variable on the controller, just pass it to the method.

public static class SomeHelper
{
    public static async Task checkUserisValid(int user_id, DataModel db, Request request, User user)
    {
       user_list user_list = await db.user_list.FindAsync(user_id);

       if (user_list == null)
       {
          throw new   HttpResponseException(request.CreateErrorResponse(HttpStatusCode.BadRequest,"This user does not exist"));
        }

        int businessID = user_list.business_id;

        var result = checkAccess(user.Identity.Name, businessID);

        if (result.Count <= 0)
        {
          throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.Unauthorized, "You do not have access to modify this business"));
        }
   }

  public static List<user_details> checkAccess(string userName, int id)
  {
      //code which checks if the user is in the right tables
          return checkAccess.ToList();
   }

}

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