Why clutter your inbox with error messages? Why make special code provisions for users to receive error messages via email? Why not log your error messages and have users subscribe to receive them in their favorite RSS aggregator?

If you are logging your exceptions already, you may find it easier to provide a syndication service. The process is ridiculously simple, and starts by creating a new project using the "Syndication Service Library" template. This template creates everything for you. All you need to do now is fill the SyndicationFeed with SyndicationItem objects.

Add a new class file called Feeds.cs:

Modify the App.config file:

You will need to adjust your project's Debug options to have command arguments that look similar to the following to F5-debug your service.

"/client:iexplore.exe" "/clientArgs:http://localhost:8000/Feeds/Errors?env=Production&app=GeoTracker"

Press F5 to test it out.

Here is the IE7 RSS viewer:

Here is your RSS aggregator viewing the same feed:

You will, of course, want to add some additional information to the content of your SyndidationItem, a bogus phrase works for this example.

Also, it is unusual that you would care to keep your exception details around for a long period of time. Since this is a syndicated feed of application errors, you should make special arrangements to archive or delete your exception log on a regular basis. This will not only keep your insert and select times low, but will also alleviate the burden placed on a new subscriber when all of the exceptions from the database appear at once. An alternative would also be to modify the LINQ in the code above to only bring back exceptions from the last 7-60 days depending on your counts. I already archive my exceptions to a master exception repository for all environments by way of an ETL job. This way I can report on my errors without disturbing the live environments too.

I decided to come out of my cave and look around 3.5 a bit. I haven't read much about extension methods, but find them quite useful. They are nothing more than a syntactically superior static helper method. Let's look at a quick example so I can get back to coming up with more excuses to use them everywhere.

I like to batch my database calls as much as possible to avoid repeated opening/closing of connections, etc. To do this, I pass a bunch of ID values into a stored procedure as a comma-separated string. In the stored proc, I break the string apart with everyone's favorite table-valued function fn_MakeTable() to make a table of IDs. Then I can JOIN, UPDATE, or INSERT as needed.

So let's say I have a collection of Orders which I can easily convert to an array of OrderID integers with LINQ. My new best friend to create a comma-separated string of OrderIDs is the following.

You'll see that I have two ToCsv() methods. The first takes a generic array using the this keyword and uses .ToString() as a default converter to string. The second method requires you to additionally pass in a converter to convert the object of type T to a string. Take those converted strings, add them to a CommaDelimitedStringCollection and .ToString() that collection to a full CSV string of integer values.

There are two ways to call these extension methods. The first is the more familiar way. Since they are really nothing more than static helper methods, call them just like any other:

The second is the more elegant and more intuitive way. Call it as if it was built into the Framework:

You may be wondering, what if I write a method that matches the signature of a built-in method like .ToString(). Well, the built-in methods take precedence over extension methods, so array.ToString() will still appear as System.Int32[]. To get your new meaning of .ToString(), you just have to call it in the static helper method way detailed above.

For a generic array of T, you will likely want to provide your own Converter if T's .ToString() method does not display the information you want to show in the CSV string. Below is a lame example of a converter. It takes the int value, converts it to the char value.

I think something so simple, and definitely re-usable, would benefit any developer.

Our friends at Microsoft may have slipped one in on us. After installing the 3.5 Framework Service Pack 1, it appears that you no longer need the [DataContract] or [DataMember] attributes on your DataContracts and DataMembers. I'm not sure what the motivation was for this "enhancement", but it caused some trouble for me the other day.

For this example I will be using the base project VS2008 gives you when you create a new WCF Service Library. I am simply adding a NestedType to the CompositeType given in the base project.

Before installing SP1, having code as it appears below would cause an error during Metadata Exchange that reads something like "Metadata contains a reference that cannot be resolved". Notice that CompositeType's NestedObject is marked as [DataMember] and also notice that the NestedType class is not marked as [DataContract] and has no [DataMember] attributes. Adding [DataContract] on NestedType and [DataMember] on IsVisible will clear this error and everything will work as expected. 

The same code in use after SP1 will not cause this error. WCF will interpret from CompositeType's [DataContract] attribute and NestedObject's [DataMember] attribute that you meant to put [DataContract] on NestedType. So what's the big deal, right? WCF is doing me a solid by guessing at what I meant to do. To me, this violates the repeated opt-in theme present in WCF. For every other important decision, the developer must write code to opt-in to a feature. For example, TransactionFlow defaults to false so we don't use the client's incoming transaction with explicitly writing code that says to do so.

This is clearly not on the same level as TransactionFlow. But why does it assume something about my objects? Why does it assume that every member of my object should be a DataMember?

I noticed this new "feature" when troubleshooting some code that had different namespace names specified in the DataContract attribute. Since the NestedType did not have a [DataContract] attribute, the namespace was using the original namespace name. The equivalent of CompositeType came through correctly, but the NestedObject had no value.

Enterprise applications store their data in a relational database. Our code reads the data stored in tables with many complex joins and business rule laden queries. We take the results of those queries and construct an equally complex business entity that is used by our application logic. Most developers, myself excluded, hate working with the database. Writing, modifying, or even seeing T-SQL causes some developers to itch. LINQ to SQL serves as a partially effective Hydrocortisone to relieve the itch. But they still need to maintain the schema, write SQL-mindful LINQ queries, and deal with the constant DataContext updates.

Imagine a world where you no longer need to translate your complex business entities to and from relational tables.  A world where there is no database backing store. A world where we create our business entities and store them in memory. Even better, in memory on a shared resource. Does it sound like an inconceivable futuristic developer heaven? Well it probably is, but this is really cool stuff in the works.

Enter the Microsoft project code-named "Velocity." The blurb on the overview page reads:

"Velocity" is a distributed in-memory application cache platform for developing scalable, high-performance applications. "Velocity" can be used to cache any CLR object and provides access through simple APIs. The primary goals for "Velocity" are performance, scalability and availability.

I have been working with the Digipede Network, the leading grid computing software solution, for a few months. The Velocity architecture sounds remarkably similar to Digipede's. I have seen the great benefits of the Digipede Network and have high expectations for Velocity.

The Digipede Network, for those of you that haven't seen it yet, consists of a central Digipede Server and one or many Digipede Agents. The server receives client requests and assigns tasks to the agents. The client uses the Digipede API to communicate with the server. The API pretty much wraps client-to-server and server-to-client WSE2 web service calls. This architecture allows you to take almost any CPU-intensive process and spread the workload among tens or hundreds of commodity or server grade machines. The result is a very high performing and easily scaled system with few code changes from what you do today.

Digipede Network Diagram:

Digipede only works in this configuration, while Velocity has two proposed deployment models. You can have a "caching tier", similar to Digipede's Server and Agent configuration, or you can house Velocity as a Caching Service directly in IIS7. I don't know how communications will be handled between the client API and the "caching tier", but I assume it will be some sort of service calls (WCF perhaps). All CLR objects stored in the Velocity cache must be marked [Serializable] just as task worker classes must be to work with Digipede.

The Velocity API looks simple enough too. It exposes intuitive Get() and Put() methods where you call the cache by name. I can see how versioning of the cached objects might get tricky. Your application will also need a new configSection that specifies the deployment mode, locality, and also contains the list of cache hosts. As this is a distributed solution, the standard virtual machine playground doesn't work too well to really test this out.

This looks promising, and I'll be following the progress of the project closely.

Download Velocity

Download the Velocity CPT 1 samples

Juval Löwy mentioned the Microsoft Service Trace Viewer in a webcast today. If you ever wondered exactly what WCF does under all of those covers, check this out.

First things first. Enable tracing on the client and host applications using the WCF Configuration Editor. Enable the verbose trace level and check all of the listener settings. This will add all of the necessary <system.diagnostics> settings in your config file. The next time you start each of the applications, a .svclog file will be created that will be used by the Service Trace Viewer.

Start your host, start your client, run through the test cases that you want to analyze in the viewer. After your test run is complete, open the viewer, located at C:\Program Files\Microsoft SDKs\Windows\v6.0A\bin\SvcTraceViewer.exe. "Open" the host.svclog file, and then "Add" the client.svclog file. Both "Open" and "Add" are menu items under "File".

Start on the Activity tab, look through the host and client activities that occurred. Everything from ServiceHost construction through ServiceHost closing shows up. This is very cool, especially when analyzing the differences between different security, session, and reliability settings.

When you are done looking through the activities, check out the Graph tab. Here you can look at the interactions between the client and host, as well as looking at the details of each activity (at the top right). At the bottom right, you will also notice the formatted and xml details of this activity.

This is a very cool tool for both debugging and training. Below is my lame test projects, if you want to skip past the configuration and check out the tool. My .svclog files are located in the Client and Host folders.

SvtTest.zip (190.32 KB)

Enjoy! Thanks to Juval for the direction.

I was looking for guidance on this topic, and came up with nothing. I'm sure people are doing this, but can't find any info. For anyone looking like I was, here's how to do it.

It's much simpler than I imagined, thanks to WCF. You can programmatically create your endpoint, binding, and channel inside your service. This would require that the address be hard-coded and require a recompile to change the address or binding. As long as your host's app.config or web.config has a client endpoint specifying the contract, you don't have to go through all that work. Your service is simply a client of another service, so your code looks just like that of a client of your service. Furthermore, changing the address or binding is as simple as changing config file values.

Service code: