How to map part of table (only for specific columns) in Entity Framework?

No, you can’t.
The workaround is to create store procedure or view, the map from there

Exporting The Razor WebGrid To Excel

http://www.mikesdotnetting.com/Article/204/Exporting-The-Razor-WebGrid-To-Excel

@{
    Layout = null;
    var db = Database.Open("Northwind");
    var sql = "SELECT CustomerID, CompanyName, ContactName, Address, City, Country, Phone FROM Customers";
    var data = db.Query(sql);
    var grid = new WebGrid(data, canPage: false, canSort: false);
    Response.AddHeader("Content-disposition", "attachment; filename=report.xls");
    Response.ContentType = "application/octet-stream";
}
@grid.GetHtml(
    columns: grid.Columns(
        grid.Column("CustomerID", "ID"),
        grid.Column("CompanyName", "Company Name"),
        grid.Column("ContactName", "Contact Name"),
        grid.Column("Address"),
        grid.Column("City"),
        grid.Column("Country"),
        grid.Column("Phone")
    )
)

How to add robots.txt into ASP.NET MVC site?

There are two ways to do so:
First one:
http://rayaspnet.blogspot.ca/2011/04/how-to-implment-dynamic-robotstxt-in.html

Second, the simpler one:
Add robots.txt into your website root, and Add one line into Global.asax file

        public static void RegisterRoutes(RouteCollection routes)
        {
            routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
            routes.IgnoreRoute("robots.txt");
        }

Inside the ASP.NET Single Page Apps Template

http://www.johnpapa.net/inside-the-asp-net-single-page-apps-template/

How to ask user if want to leave current page in JavaScript?

Add function into onbeforeunload

var unsavedChanges = false;
window.onbeforeunload = function() {
  if (unsavedChanges) return 'You have unsaved changes!';
}

https://developer.mozilla.org/en-US/docs/DOM/window.onbeforeunload