Dirk.Net

One of the most (in)famous marketing ploys of the not-so-recent past was the .NET pet store, where Microsoft showcased the new .NET framework in an ASP.NET web application with similar functionality as the erstwhile Java PetStore, using vastly less code. It also performed and scaled much better on all benchmarks conducted by Microsoft.

Sure enough, there’s a pet store done in Ruby on Rails as part of the ThoughtWorks Commons project, used mainly for scalability “shootouts”. Check it out and poke around to learn how things are can be done. There are actually two pet stores with PetStore2 more of an AJAX/Web 2.0  site. As complete sample rails apps for free download seem to be hard to come by here’s one option that can be used for learning as well as for speed tests. Hope it helps.

One of the greatest time-wasters using Visual Studio is navigating the Solution Explorer looking for files to open or edit. With multiple projects and more files and folders for each project it just gets worse and worse. So Chris O’Sullivan created this little Visual Studio Plugin to quickly find files to open and edit without leaving the keyboard. Lars Engel has improved it to work with Visual Studio 2003 (and 2005). Be sure to follow the installation instructions on Chris’  site.

The free DPack Package offers this functionality as well (besides many other goodies) with a version for Visual Studio 2008 (aka Orcas) in the pipeline and the benefit of enabling the selection of multiple files.

Of course Netbeans has this functionality built-in (Navigate>Go to file…, or Alt-Shift-O) in a fast and functional implementation which also lets you open multiple files in one go. In Eclipse/Aptana/RadRails it’s Navigate>Go to>Resource or Alt-Shift-R on the keyboard with only single files selectable. Hope it helps.

Not sure if it’s actually released or not but if you’re looking for a snappy and complete IDE for Ruby on Rails you should try Netbeans 6.0 in the Ruby flavor, a mere 19 MB download (well, you’ll need a JDK too). The joy of RoR development is greatly enhanced by such an intelligent IDE where Ruby and Rails take center stage instead of being added as an afterthought as with some competing offerings. It’s amazing that the developer team was able to iron out quite a number of bugs in the two weeks since I downloaded a nightly built. Other people like it too.

To backup, replicate or mirror a repository is arguably one of the most important tasks working with Subversion. Of course a repository folder is completely self-contained and can be copied or ftped to a different location and read by svn without any problems as long as there is no writing or locking going on. Besides the simple copy there are several safer and more svn-specific options, three of which are discussed in this article. However, the suggested svnadmin hotcopy command like most svnadmin works only with paths, not URLs. So you have to enter (Windows):

C:\>svnadmin hotcopy c:\myrepos \\MYBACKUPSERVER\C\myrepos_bak

This technique works fine on your local network where you have path access as it’s fast and simple to use.

Since version 1.4 Subversion offers the svnsync utility which maintains read-only mirror of a subversion repository at a (remote) URL. It words by replaying revisions of the original (source/master) repository at a mirror (sink) repository.

The setup notes are meant for Unix machines and not easy to understand for newbies. Follow these steps to get it working on a Windows machine:

1. Set up a sync user on the destination repository by editing the passwd file in the conf directory of the target repository:
   [users]
   #harry = harryssecret
   #sally = sallyssecret
   mysvnsyncuser = mystrongpassword
2. This “syncuser” you created must be allowed to change revprops of the destination repository used by svnsync to keep track of bookkeeping information. Therefore a pre-revprop-change hook script has to be created. You will find an example script in the /hooks/pre-revprop-change.tmpl file of your target repository. However, this script is a Unix shell script and will not work under Windows. You will get the following error if you don’t have a script in the hooks folder that can be executed by Windows:

   svnsync: Repository has not been enabled to accept revision propchanges;
   ask the administrator to create a pre-revprop-change hook

   The simple solution is just to create a file named pre-revprop-change.bat containing the single line:
   @exit 0
   and save this file file in the /hooks directory of the target repository.

3. Then svnsync has to be initialized with the command:
   svnsync init svn://mytargetserver/mytargetrepository svn://mysourceserver/mysourcerepository
   (you can use any other URL such as file:, http:, svn+ssh:)
   You will be prompted for the username and password you created for the mysvnsycuser above.
   If all went well you will get the response:
   Copied properties for revision 0
4. You can now sync with the command:
   svnsync sync svn://mytargetserver/mytargetrepository
   and all revisions to your source repository will be replayed to the destination repository.
5. In Windows you could set up a Scheduled Task to sync from time to time which is beyond the scope of this article.
6. Don’t forget: NEVER commit to a synced repository without “svnsync” or you’ll get the “have you committed to the destination without using svnsync?” error and you’ll have to start over with the above process.

Hope it helps.

Sometimes I miss the option that you have in classic ASP, PHP or Ruby on Rails to just put a nested loop into the html page (view, presentation layer) to display nested data. Of course this is, strictly speaking, against ASP.NET best practices where you’re supposed to use web controls for everything. Then again one could make the argument that the loop actually belongs in the view. This would be .aspx page, and not in the controller or the model (code behind file in ASP.NET).

The task at hand is to iterate through parent categories and child items. The technique suggested by Microsoft is outlined here, and this article uses a nested repeater with a self-join. Starting point is the following DataSet with two related tables and a repeater in the page:

                 DataSet myDS = new DataSet("NestedRepeaterDemo");
                … //fill the dataset                

                myDS.Tables[0].TableName = "ParentCategories";
                myDS.Tables[1].TableName = "ChildItems";
                DataRelation relation = new DataRelation("myRelation",
                 myDS.Tables["ParentCategories"].Columns["CatID"],
                 myDS.Tables["ChildItems"].Columns["CatID"], true);
                relation.Nested = true;

                myDS.Relations.Add(relation);
                parentRepeater.DataSource = myDS;

                parentRepeater.DataBind();

So why not bind the child repeater in the page, just for the heck of it:

<table>
<asp:Repeater id="parentRepeater" runat="server">
    <itemtemplate>
        <tr class="categoryInTable">
        <td colspan="2">
         <%# DataBinder.Eval(Container.DataItem, "CategoryName") %>
         </td>
        </tr>

        <asp:Repeater ID="childRepeater" runat="server" datasource=’<%# ((DataRowView)Container.DataItem).Row.GetChildRows("myRelation") %>‘ >
        <ItemTemplate>
    <tr><td>
                     <%# Eval("ItemName")%>
                      </td>
                       <td>
                     <%# Eval("ItemDescription")%>
                       </td>
        </tr>
         </ItemTemplate>
        </asp:Repeater>
    </itemtemplate>
</asp:Repeater>
</table>

Sure enough with this code you will run into a DataBinding: ‘System.Data.DataRow’ does not contain a property with the name x error. 

As a quick explanation for this error the following might suffice:

When the nested repeater binds to its datasource calling the GetChildRows command of the parent DataRowView.Row object the latter returns an array of DataRows (the “child rows”, an object of type DataRow[]) which each repeater Item will be bound to now. However, Eval with the above syntax will only bind to named fields of a DataView object that exposes a name property for each field. The DataRow returned by GetChildRows is merely a row in a table without the name properties so that each field can be accessed only with an indexer (DataRow["ItemName"]).

This is why you can either change the binding expressions above like so:

                       <td>
                     <%# Eval("[\"ItemName\"]")%>
                      </td>
                       <td>
                     <%# Eval("[\"ItemDescription\"]")%>
                       </td>

or you can change the datasource to use the CreateChildView of the DataRowView directly like this:

<asp:Repeater ID=”childRepeater” runat=”server” datasource=’<%# ((DataRowView)Container.DataItem).CreateChildView(”myRelation”) %>’ >

and use old data binding syntax <%# Eval (”ItemName”) %> because now you have a DataView again (just like in the parentRepeater) which supports binding to the data field by name. Of course you have the option to do all the databinding in the code-behind file (usually the ItemDataBound event of each repeater) which gives you better debugging support than the approach above.

I find this “nested data” stuff overly complicated in ASP.NET, especially compared with how easy it is with Ruby on Rails. The plethora of objects which each behave differently is difficult to work with and the Repeater itself is limited in its built-in functionality and designer-support.

Sure enough I also ran into the

Compiler Error Message: CS0246: The type or namespace
name ‘DataRowView’ could not be found (are you missing a
using directive or an assembly reference?)

which IMHO is clearly a bug in ASP.NET as a reference to System.Data exists in the code-behind file that the .aspx web form inherits from. This issue can be fixed by either having an <%@ Import Namespace=”System.Data” %> tag in your aspx file or declaring DataRowView with the full namespace System.Data.DataRowView in the page each time.

For an in-depth view of the binding issues see this article. You might also find this post helpful.