How to convert ASP.NET website to ASP.NET web application

Well, it turns out that the option “Convert to web application” does NOT exist for “websites”. The option “Convert to web application” does exist only for “web applications” !!!!

[emphasis mine]

So, here’s the deal, to do the
conversion, you need to:

• Add a new “Web Application” to your VS 2008 solution (File->Add->New
  Project->C#->Web->ASP.NET Web
  Application).

• Afterwards, you copy all the files in the old “website” to your newly
  created “web application”, and
  override any files created in it by
  default

• The next step is the most ugly, you need to “manually” add the references
  in your “website” to the new “web
  application”. I thought the VS 2008
  PowerCommands toy would do this for me
  as it does copy references from other
  project types, but it didn’t. You have
  to do it by yourself, manually, and
  you have to be cautious in this step
  if you have multiple versions of the
  same assembly (like AJAXToolkit in my
  case) or assemblies that have both GAC
  and local versions or so.

• Keep repeating the last step and trying to build the “web application”.
  You’ll keep getting errors like ”
  ‘….’ is unknown namespace. Are you
  missing an assembly reference? “. Make
  sure you have none of those except the
  ones where ‘….’ is replaced by the
  IDs of the server controls you use. In
  other words, keep adding references
  and building the project until only
  the errors that exist because of
  missing .DESIGNER.CS or .DESIGNER.VB
  files.

• Afterwards, go to the “web application” root project node in VS
  2008 solution explorer, and right
  click it, then you WILL find the
  option “Convert to web application”.
  What this option does is actually
  making small changes to the “@Page”
  and “@Control” directives of pages and
  controls, and creating the required
  .DESIGNER.CS or .DESIGNER.VB files.

• Try building the “web application” again. If you get errors, see what
  references may be missing and/or go
  click the “Convert to web application”
  again. Sometimes, if there’s any error
  other than those caused of missing
  DESIGNER files, not all the
  pages/controls will have those
  DESIGNER files created for them.
  Fixing the non DESIGNER problem and
  clicking “Convert to web application”
  again should do the job for this.

• Once you are done successful VS build, you should be ready to go.
  Start testing your web application.
  Optionally, you can right click the
  “web application” root project node in
  VS 2008 Solution Explorer and click
  “Properties” then go to the tab “Web”
  to set the “web application” to a
  virtual folder in IIS (you can create
  new virtual directory from there in
  VS). If you want to use the IIS
  virtual directory that the old
  “website” used, you need to remove
  that from IIS first.

• Update: When testing your pages, pay MOST ATTENTION to classes in
  “App_Code” folder, especially those
  with NO NAMESPACE. Those can be a big
  trap. We had a problem with two
  extension method overloads in the same
  static class that had no namespace,one
  extends DateTime? (Nullable)
  and calls another overload that
  extends DateTime itself. Calling the
  other overload as extension method
  passed VS 2008 compilation and gave us
  a compilation error ONLY IN RUNTIME
  (With IIS). Changing the call to the
  other overload from calling it as
  extension method to calling it as
  normal static method (only changing
  the call in the same class, calls from
  other classes remained extension
  method calls) did solve this one, but
  clearly, it’s not as safe as it used
  to be in VS 2005. Especially with
  classes with no namespaces.

• Update2: During the conversion, VS 2008 renames your “App_Code” to
  “Old_App_Code”. This new name sounds
  ugly, but DO NOT RENAME IT BACK. In
  the “web application” model, all code
  will be in one assembly. In runtime,
  the web server does not know what web
  project type you are using. It does
  take all code in “App_Code” folder and
  create a new assembly for it. This
  way, if you have code in folder named
  “App_Code”, you’ll end up with RUNTIME
  compilation errors that the same types
  exist in two assemblies, the one
  created by VS, and the one created by
  IIS / ASP.NET Development Server. To
  avoid that. leave the “Old_App_Code”
  with the same name, or rename it to
  ANYTHING EXCEPT: “App_Code”. Do not
  place any code in such “App_Code”
  folder and prefereably do NOT have a
  folder with such name in your “web
  application” at all.

I know this since before but forgot it
now as I have not used “website” model
for long :(.