.Net ramblings
# Sunday, 16 January 2005
SQL - change object owner for multiple objects

Tibor Karaszi showed how to do this time saving technique on a newsgroup post. You can use the sp_changeobjectowner stored procedure in the Master database to change the owner of an object one at a time, but there is a semi-automatic way to do it.

Open query analyser, change the selected database to the on you want to work on. The following query generates a list of exec commands for all the sprocs and UDFs in the database:


SELECT 'EXEC sp_changeobjectowner ''dbo.' + ROUTINE_NAME + ''', ''thenewuser'''
FROM INFORMATION_SCHEMA.ROUTINES
WHERE ROUTINE_SCHEMA = 'dbo'

Execute it, then click the top left corner of the output window, to select all the rows. Copy and paste the rows into a new query window and execute.

To change table owners, modify the query and repeat the proces:

SELECT 'EXEC sp_changeobjectowner ''dbo.' + TABLE_NAME + ''', ''thenewuser'''
FROM INFORMATION_SCHEMA.TABLES

Sunday, 16 January 2005 18:37:40 (GMT Standard Time, UTC+00:00)  #    Comments [2]  Database

# Friday, 17 December 2004
[FIX] aspx validation not working + buttons not clicking

when i deployed my web app to the production server, i found that none of the client-side validation was working. 

the first problem was that there was no mime-type set up on the server for .js files, so i added "application/x-javascript" for the .js extension.

the next problem was that the script references in my aspx pages did not match the script location on the server.   the html source of one of my pages had the webuivalidation.js path set to /aspnet_client/system_web/1_1_4322/WebUIValidation.js

but the server directory was "/aspnet_client/system_web/1_1_4322_0/WebUIValidation.js"

so i tried duplicating the directory so that i would have both paths on the server, but that caused strange problems on the aspx page, such as buttons not clicking (when the event handlers are definitely registered). 

so what i did was run aspnet_regiis -i on the server to make sure all the script maps are registered properly, and it worked. 

if you don't have control over the web server, you can add the following to your web.config

<system.web>
  <webControls clientScriptsLocation="/aspnet_client/system_web/1_1_4322_0/" />
  ...

Friday, 17 December 2004 12:46:46 (GMT Standard Time, UTC+00:00)  #    Comments [1]  Asp.Net

# Wednesday, 15 December 2004
Can't debug web projects with VS 2003 after installing VS 2005

Can't debug web projects with VS 2003 after installing VS 2005

Fortunately Fahad Khalil found the answer to this, he posted this simple solution on his blog.

I am reproducing it here for my own records. Shoot your IIS Console, then click on the Default Website and click on Properties. You will see a Brand new shiny tab [labelled ASP.NET] ... courtesy VS .NET 2005 :). Select the correct version i.e. 1.xx :)

Cheers Fahad. Saved me a lot of work.


Wednesday, 15 December 2004 10:58:09 (GMT Standard Time, UTC+00:00)  #    Comments [1]  Asp.Net

# Sunday, 05 December 2004
An intelligent 404 page, suggest pages with a similar name to the requested page

 

Introduction

Did you ever notice on big sites like microsoft.com, if you reach a page that doesn't exist, they don't just say "Sorry, 404.", they give you a list of pages that are similar to the one you requested.  This is obviously very nice for your users to have, and it's easy enough to integrate into your site.  This article provides source code and explains the algorithm to accomplish this feature. Note: the real benefit of the approach outlined here is the semi-intelligent string comparisons.

Background

The need for this grew out of a client of mine who was changing content management system, and every url in the site changed, so all the search engine results came up with 404 pages. this was obviously a big inconvenience, so i put this together to help users find their way through the new site when arriving from a search engine.

See it in action

Go to the following page http://www.iserc.ie/December15-ISERCWorkshoponTesting.html (which doesn't exist), and the 404 page should give you a list of pages that have quite similar names.

Requirements

  • Your web site must be set up so that 404 pages get redirected to a .net aspx page
  • You must have some way of getting an array of all the page urls in your site that you want to compare 404 requests against. if you have a content management system, there is probably a structure of all the pages stored in xml or a javascript array (for DHTML menus or something), or you could write your own query to get the pages from a database. if don't use a content management system, you could hard-code a string array variable in the 404 page code behind containing the page names, or think up some way of dynamically reading all the .aspx or .html pages from the file system.
  • When the 404 page is accessed, you need to know which page was requested. Using web.config, you can set up 404 errorCodes to go to /404.aspx, where it will tag on the requested page to the querystring. the source code here assumes you have this approach, but you can obviously change it to your own needs, simply change the GetRequestedUrl() function.

Why Regular Expressions are not enough

To compare strings, you can use System.String.IndexOf or you can use regular expressions to match similarities, but all these methods are very unforgiving for slight discrepancies in the string. in the example url above, the page name isDecember15-ISERCWorkshoponTesting.html but under the new content management system, the url is December 15 - ISERC Workshop - Software Testing.html, which is different enough to make traditional string comparison techniques fall down.

So i looked around for a fuzzy string compare routine, and came across an algorithm written by a guy called Levenshtein. His algorithm figures out how different 2 strings are, based on how many character additions, deletions and modifications are necessary to change one string into the other. This is called the 'edit distance', i.e. how far you have to go to make 2 strings match. This is very useful because it takes into account slight differences in spacing, punctuation and spelling. I found this algorithm on http://www.merriampark.com/ld.htm where Lasse Johansen kindly ported it to C#. The algorithm is explained at that site, and it is well worth a read to see how it is done.

Normalising the Scores

I originally had a problem with the algorithm because it gave surprising results for certain situations. If the 404 page request was for 'hello' and there is a valid page called 'hello_new_version' and another valid page called 'abcde', then the 'abcde' page gets a better score, because fewer changes are needed to make it the same as hello (just change the 5 characters in 'abcde' into 'hello'). this is 5 changes, even though the 'hello_new_version' is semantically a better match. Fortunately, a kind newsgroup participant named Patrice suggested that i divide the score by the length of the comparison string, to normalise the results. This worked perfectly, and i found that a score between 0 (perfect match) and 0.6 (a good match) is worth including as a suggested page. You can change this value in the ComputeResults() method if you want to make it more or less flexible.

Code Summary

private void Page_Load(object sender, System.EventArgs e)
{
   GetRequestedUrl();
   SetUpSiteUrls();
   ComputeResults();
   BindList();
} 

The above code shows the 4 key tasks that make up this solution. Each method is explained below.

Using the code

  1. GetRequestedUrl() simply figures out which page was requested. In this example, it is assumed that your web.config contains the following:
    ***In this example, the querystring on the 404.aspx page contains the requested url. SetUpSiteUrls() is where you load in all the pages in your site. In my content management system, i have an xml file with all the names, so i do an XPath query and add in the names one by one to the arraylist.
  2. private void SetUpSiteUrls()
    {
      this.validUrls = new ArrayList(); 
      /*
      * Insert code here to add the pages in your site to this arraylist
      */ 
    }
  3. ComputeResults() iterates through the urls you set up in SetUpSiteUrlsreturns and attaches a score of how close each one is to the requested url. It also sorts the results and discards any that are not a close match.
    private void ComputeResults()
    { 
        ArrayList results = new ArrayList(); // used to store the results 
        // build up an arraylist of the positive results 
        foreach(string s in validUrls) 
        {
            // don't waste time calculating the edit distance of nothing with something 
            if(s == "") continue; 
            double distance = Levenshtein.CalcEditDistance(s, this.requestedUrl); // both in lower case 
            double meanDistancePerLetter = (distance / s.Length); // anything between 0.0 and 0.6 is a good match. the algorithm always returns a value >= 0       
            if(meanDistancePerLetter <= 0.60D) 
            { 
                // add this result to the list. 
                results.Add(new DictionaryEntry(meanDistancePerLetter, "<a href='" + s + ".html'>" + s + "</a>")); // use dictionary entries because we want to store the score and the hyperlink. 
                // can't use sortedlist because they don't allow duplicate keys and we have 2 hyperlinks with the // same edit distance. 
            }
        }
        results.Sort(new ArrayListKeyAscend());
    }
    IMPORTANT NOTE: One thing to definitely look out for is the inner-most line of the above code. results.add(new DictionaryEntry(...). I am adding in a html hyperlink, with the name of the page + ".html". This may not be a correct link in your web site, because you may have removed the folder part of the url while populating the validUrls arraylist. You may need to expand the data structures used in this code to include full url for each page.

  4. BindList() simply binds the arraylist of results to the datagrid, which is configured to display them in a bulleted list.
    private void BindList()
    {
        if(results.Count > 0)
        {
    
            this.lblHeader.Text = "The following pages have similar names to " + this.requestedUrl + "";
            this.DataList1.DataSource = results;
            this.DataList1.DataBind();
        }
        else
        {
            this.lblHeader.Text = "Unable to find any pages in this site that have similar names to " + this.requestedUrl + "";
        }
    }

The 'magic' in the code is all done with the Levenshtein.CalcEditDistance method which returns the distance between 2 strings. It is included in the source.

Winforms Test Application

If you're interested to test out the levenshtein algorithm, i've written a windows forms application that lets you enter a string (e.g. a page url) and also a list of strings to compare it against (e.g. all the page urls in your site), and it gives you the 'edit distance' scores. download here (7k)

Comments

I think this is a great feature because it adds significant value to the user experience for a web site. Please feel free to comment below if you have any questions, find any bugs, improvements, or if you can't get it working, or if you use it in a novel way.

Enjoy!


Sunday, 05 December 2004 15:15:28 (GMT Standard Time, UTC+00:00)  #    Comments [0]  Asp.Net

# Monday, 22 November 2004
How to disable new rows in Windows Forms DataGrid

i found a few work arounds to prevent a datagrid from displaying the * new row. one of them involved using a dataview as the datasource, with AllowNew property set to false. however, someone called Sameers from theAngrycodeR pointed out that a datatable has a DefaultView property which also has this AllowNew property. so you can use the following code (if your datasource is a dataset):

this.dataSet1.Tables[0].DefaultView.AllowNew = false;

and you get to keep the dataset or datatable as the direct datasource.


Monday, 22 November 2004 17:05:24 (GMT Standard Time, UTC+00:00)  #    Comments [0]  .Net Windows Forms

Using custom datatypes in a .Net Dataset

Background

In my content management system, i allow the user to define their own 'objects' (e.g. Staff Member) and then i provide templated data entry forms to let them populate instances of these objects.  It's aimed at non-techies so i have my own datatypes called 'Text' which maps to System.String, 'Number' maps to System.Double etc.  I also have a few custom data types called 'File' and 'Image' to allow the user to add files or images to an instance of the object. 

Problem

This business of doing column-mapping was ok as long as my data types had obvious .Net equivalents, but 'Image' doesn't in my case. i'm only storing a reference to the image, but in my application, it's not to be treated just as a System.String.  When the user is creating a new object with an 'Image' field in it, i want to display a file upload instead of a textbox, and when i go to display the object on the site, I want to display a html IMG tag with the SRC set to the value of the image field. 

Solution

The dataset is serialised into an xml file with the schema embedded. i needed to find some way of encoding my own custom data type information into the dataset that would persist into the xml file.  I looked through the VS intellisense and found the 'ExtendedProperties' data column property.  This property allows you to plug in any number of key/value pairs of information to each column.  This was exactly what i needed, so i added in a pair with something like "MyDataType=Image" for each column.  This persisted nicely into the xml file as follows:

<xs:complexType>
  <xs:sequence>
     <xs:element name="Photo" msprop:MyDataType="Image" type="xs:string" minOccurs="0" />

Note that the official type of the field is "xs:string", because it contains a path to the image. but now it also has the custom data type tagged on to the column definition. in this respect, i'm glad to see that MS have provided a very elegant and flexible framework.


Monday, 22 November 2004 16:53:35 (GMT Standard Time, UTC+00:00)  #    Comments [0]  .Net General

# Thursday, 18 November 2004
System.Net.WebException: The request failed with HTTP status 401: Unauthorized.

I have a WSE2 web service that was working fine until one day i got the above error.  i realised i had changed the permissions on the folder (for the web application), so that only System, Adminstrators and ASPNET had permissions on it.  Previously the 'Users' group had permissions.  By a process of elimination, i found out that IUSR_xx needed to have read/execute permissions aswell as ASPNET, even though the process is running with the identity of ASPNET. 

it's strange, but i thought i'd post my solution here in case anyone else comes across this.


Thursday, 18 November 2004 12:45:53 (GMT Standard Time, UTC+00:00)  #    Comments [5]  Asp.Net

# Monday, 08 November 2004
Asp.Net DataGrid PageIndexChanged not working

i have an asp.net custom server control (deriving from a datagrid) and it has built in paging, sorting and databinding.  i ran into a weird problem, and thanks to Rick Strahl's post on http://west-wind.com/weblog/posts/211.aspx i was able to get it working.  Read that page first because there are many solutions posted for this weird error.

i'm using regular paging, and the next button works fine (all the time, for multiple pages), but if i click previous then a dud postback happens and the pageIndexChanged event doesn't fire.  i'm 100% sure that the eventhandler is hooked up, it just doesn't fire.  the solution in my case was to bind the datagrid in the control's PreRender method instead of in the OnInit method.  it just worked fine after doing this. 


Monday, 08 November 2004 18:33:01 (GMT Standard Time, UTC+00:00)  #    Comments [0]  Asp.Net

# Wednesday, 03 November 2004
using the same WSE2 web service with 2 different policies..

did you know you can configure multiple policies for the same web service?  it's possible because endpoint uri's are case-sensitive, so you can have WebService1.asmx and WEBSERVICE1.asmx, which are treated as separate web services in the policyCache.config file. see the sample below:

<endpoint uri="http://localhost/winDB.asmx">
 <defaultOperation>
  <request policy="#username-token-signed" />
  <response policy="" />
  <fault policy="" />
 </defaultOperation>
</endpoint>

<endpoint uri="http://localhost/WINDB.asmx">
 <defaultOperation>
  <request policy="" />
  <response policy="" />
  <fault policy="" />
 </defaultOperation>
</endpoint>

the first one uses a username-token-signed policy for authentication.  clients who wish to use this policy must have a reference to the web service matching the case of the endpoint uri exactly. 

the second endpoint has no policy enforcements and this means even a non-WSE request can use the web service.

some WSE implementations, (especially custom username tokens..) will have a method like "checkAuth()" that every web method calls at the start to verify programattically that the message obeys the rules.  this method throws soap faults for any missing WSE elements in the message header.  in my case, i want to allow requests originating from the web server itself (.aspx pages using the web methods) to bypass the authentication checks, so i put the following lines of code at the top of my "checkAuth()" method to allow requests made on the same server to go through:

// allow local ws requests to bypass security
if(HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"].ToString() == "127.0.0.1")
  return;  // skip further checks

i could also invoke the web methods using the web service class directly, (not go through a web service proxy) because it's within the same assembly, but i'm sure there are circumstances where this approach may prove useful.  if you find any, post them here as a comment, i'd be interested to hear.  


Wednesday, 03 November 2004 17:43:16 (GMT Standard Time, UTC+00:00)  #    Comments [0]  Asp.Net

# Tuesday, 26 October 2004
TextBox.Focus() doesn't work within Form_Load

i have a windows form with a textbox inside a panel, and the following code doesn't work as expected:

private void WizardLoad(object sender, System.EventArgs e)
{
  this.txtUsername.Focus();
}

Thanks to someones post

i now know that the best way to do it is as follows:

this.ActiveControl = this.txtUsername;

It works!


Tuesday, 26 October 2004 12:06:57 (GMT Daylight Time, UTC+01:00)  #    Comments [1]  .Net Windows Forms