Thread: Simple VirtualPathProvider to stream ASP.NET code from a database C#

I wanted to put together some code examples for a website that also included examples of the code working. Rather than create a new .aspx file for each example, I wanted an easier way to create the working examples. JMH pointed me to the VirtualPathProvider as a means of achieving this.

Many examples that I looked at were a little over complicated to get a grasp of the basic concept, so I came up with the code below as an example of how I got it to work.

Obviously, this example can be built on to include caching of the pages, updating of the code etc. but I just wanted to share this example for starters. Once I play around with it a bit more, I'll try and post updates and improvements

It's also written in C#, so will try and convert it to VB when I have 5 minutes.

myVirtualProvider.cs

Code:

using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Security.Permissions;
using System.Web;
using System.Web.Hosting;
using System.IO;
//the following 2 namespaces are from my own app. You can point to any DAL or BLL namespaces you have in your
//own app
using w3d.App.BLL.Globals;
using w3d.App.BLL.Codes;
 
namespace w3d.App.BLL.myVP
{
 
    public class myVirtualProvider : VirtualPathProvider
    {
 
        //checks if the current url folder starts with our designated "virtual" folder
        private bool IsPathVirtual(string virtualPath)
        {
            String checkPath = VirtualPathUtility.ToAppRelative(virtualPath);
            return checkPath.StartsWith("~/virtual".ToLower().ToString(), StringComparison.InvariantCultureIgnoreCase);
        }
 
        //MUST OVERRIDE function checks if the file exists in your virtual file system
        //Many web examples use a cache to store the virtual files for faster access
        //in which case you'd have to check for the key value in the cache
        public override bool FileExists(string virtualPath)
        {
            if (IsPathVirtual(virtualPath))
            {
                //checks if the virtual file exists in my codes object. This calls a function that
                //queries the db with the value held in virtualPath.
                //Assuming the path to your virtual file was www.domain.com/virtualFolder/virtualFile.aspx
                //then virtualPath would contain /virtualFolder/virtualFile.aspx
 
                if (codes.CheckIfFileExists(virtualPath))
                    return true;
                else
                    return false;
            }
            else
            {
                return Previous.FileExists(virtualPath);
            }
        }
 
        //MUST OVERRIDE function retrieves the file from the virtual file system as a new virtualfile object
        public override VirtualFile GetFile(string virtualPath)
        {
            myVirtualFile file = new myVirtualFile(virtualPath);
            if(file.fileContent == null){
                return Previous.GetFile(virtualPath);
            }else{
                return file;
            }
        }
 
        //default constructor for the Virtual Path Provider
        public myVirtualProvider() : base()
        {
            //
            // TODO: Add constructor logic here
            //
        }
    }
 
#region "myVirtualFile"
    //Virtual file object inherits from VirtualFile
 
    public class myVirtualFile : VirtualFile
    {
        //String property to contain the code to be streamed
        public string fileContent;
 
        //default Constructor for the Virtual File Object. Populates code string
        public myVirtualFile(string VirPath)
            : base(VirPath)
        {
            //retrieves the code text from a function in my codes object
            fileContent = codes.GetCodes(VirPath);
        }
 
        //MUST OVERRIDE. Streams the code string to a Stream object.
        public override Stream Open()
        {
            Stream stream = new MemoryStream();
            if (fileContent != null || fileContent.Equals(String.Empty))
            {
                // Put the page content on the stream.
                StreamWriter writer = new StreamWriter(stream);
                writer.Write(fileContent);
                writer.Flush();
                stream.Seek(0, SeekOrigin.Begin);
            }
            return stream;
        }
    }
#endregion
}

The virtual path provider is registered in global.asax Application_Start. Many examples I saw use AppInitialize in the class but this didn't seem to work for me.
global.asax

Code:

.
.
<%@ImportNamespace="w3d.App.BLL.myVP" %>
<%@ImportNamespace="System.Web.Hosting" %>
.
.
Sub Application_Start(ByVal sender AsObject, ByVal e As EventArgs)
' Code that runs on application startup
HostingEnvironment.RegisterVirtualPathProvider(New myVirtualProvider())
EndSub 

That's basically the virtualpathprovider setup. You also need to add the virtual folder into your directory hierarchy. In my case I just added a folder called virtual in the webroot.
My database was setup like this (this is in MySQL)

Code:

coderef INT autoincrement
title VARCHAR (255) just used as link text in a datalist of all the code examples
code longtext
code_file VARCHAR (30) 

Obviously code contains the data to stream and code_file contains the virtualPath value to check against.
I have only tested this with inpage coding so far, not code behind. You also need to make sure any links to physical files in your site include ~/ at the beginning. This includes any master pages etc.

You can also stream master pages, user controls and html files.

Hope that helps. I will post any updates I have and once I have a more complicated example, with caching, directories etc. then I'll post that as an Advanced Example.

I am currently working on creating a siteMapNode for the file for my web.sitemap hierarchy. I have written another example on adding siteMapNodes dynamically, which is located here....Adding dynamic SiteMapNode to SiteMap when using VirtualPathProvider

Just as a minor update to this, you can use code behind files in exactly the same way.

Set the CodeFile in your content page to include the "virtual" folder and the filename, with correct extension, and then include the code in your database as a seperate file with the name used in your CodeFile parameter.