CustomMembershipProviderEntities could not be found

Hello I'm trying to create a custom members area docs.sitefinity.com/custom-membership-provider-create-the-custom-membership-provider-class. Im following this tutorial, however i get stuck when i need to create the method below. 'CustomMembershipProviderEntities cannot be found are you missing a reference'. Visual Studio doesnt  pick this up in any assembilies. I'm new to Sitefinity so far ive created a new project in the project manager, opened it in visual studio as a website as no solution was present, saved a solution and opened that, it compiles fine. Ive then just started on this tutorial. 

    public CustomMembershipProviderEntities ProviderEntities
   
        get;
        set;
   

I think I've sussed it. I closed the solution, just opened the project inside the site root, this seems to be able to access the class ok from the MembershipModel.Context.cs. Not sure why the solution cant!