The Microsoft.Data.Dll Brouhaha

by jmorris 3. August 2010 13:45

There has been a lot of noise in the dotnet blogasphere regarding Microsoft's latest offerings, Microsoft.Data.DLL and WebMatrix...most of it negative:

To get a feeling for the community sentiment on these two ms products, you really need to read through the comments! It seems that a lot of dotnet developers are miffed with MS for releasing these tools which, according to contemporary software architecture standards, promotes poor practices and the development of security ridden software.

Understandably, the community is upset sense they have been pushing MS (we all know MS’s record with quality software) towards the acceptance of better software development practices for some time now and releasing an API intending to promote bad practices is counter-intuitive. To Microsoft however, this is an opportunity to reduce the barriers of entry to MS offerings and provide API’s similar to some of the PHP offerings like Drupal and Wordpress, which currently have a huge market share.

If you’re wondering what Microsoft.Data API is, it’s simply a couple of wrappers over raw ADO.NET…nothing different from any of the wrappers we have all created in the past. It’s very similar to using the Enterprise Data Access Library with updated syntax and language features found in dotnet 3.0 and better. It basically allows developers to declaratively combine data access and markup on a webpage much like PHP developers do now (and PHP consultant’s en masse). An architectural Achilles’ heal with respect to maintenance, but a boon to quick n’ durty development…exactly user base MS is targeting (and largely owned by the PHP/ROR crowd).

Will I ever use Microsoft.DLL API or WebMatrix? Probably not…however I question the wisdom in a strategy that alienates one core developer group (professional) in an effort to gain another developer (amateur) which is clearly not even interested.

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ActiveMQ via C# using Apache.NMS Part 2 - Queues

by jmorris 29. July 2010 13:35

ActiveMQ via C# Part 2
In my part 1 of this series, I discussed the basics of JMS and messaging schematics: publish/subscribe and sender/receiver. I introduced Apache.NMS and the ActiveMQ client for NMS, Apache.NMS.ActiveMQ. I created client classes for publishing messages to ActiveMQ via topics and subscribing to a topic to receive messages. Finally, I tested the classes by writing a unit test that contained a publisher that sent messages to a topic and a subscriber that wrote the output to the console. In this example, I will expand on C# client by writing a simple, reusable configuration based API for sending and receiving messages using ActiveMQ and Apache.NMS.

In situations where you have multiple projects in need of a common messaging infrastructure, relatively low messaging domain knowledge across teams and an integration requirement between .NET and other Java based systems, a simple wrapper over a more complex JMS/NMS API can quicken client development. Additionally, the JMS/NMS programming model lends itself to a configuration based API that utilizes factory methods to create configured objects for sending and receiving objects.

The benefit of going with this model is that users of the API can get up and running quickly and need very little understanding of the nuances of JMS/NMS. Also, APIs like this make it easier to manage deployments amongst the different software environments in most organizations: dev, staging, prod, etc.

More Messaging Schematics
JMS provides two major schemes for sending and receiving messages: point-to-point (PTP) and publish/subscribe (Pub/Sub). PTP messaging is always queue based, while the Pub/Sub model uses topics.

In JMS speak topics and queues are simple message destinations or channels that producers send messages to and consumers listen to via notification semantics that messages are available. For topics, each consumer that subscribes to a topic will receive a copy of a message if the consumer is an active subscriber at the time the broker receives the message. If a producer sends a message to a destination and there are ten consumers actively subscribing to the destination, all ten consumers will receive a copy of the message. Pub/Sub is useful in which you want every consumer or client to receive a message sent to a destination by a producer:

On the other hand, queues are like load balancers: if a producer sends a message to the destination, then the message will be kept by the broker until a consumer is available and then the message will be delivered. Note that if there is one producer and ten consumers of the queue, exactly one consumer will receive a copy of the message. The messages are load-balanced in that if another message is sent, the next consumer will receive a copy of the message and then the next, and so on and so forth as messages are sent to the destination. A scenario where this is useful is where you have say a pool of processes and you want each message sent to the pool to be received by a single process and each subsequent message to be processed by exactly one other, different process within the pool.

In part 1 I created a consumer and producer of messages using pub/Sub schematics, in this example I will augment this API with classes for sending message using PTP messaging schematics. These classes will allow clients to send and receive messages to queues with consumers of these messages receiving at most one copy of the message that was sent from a producer. Additionally, I’ll provide a simplified API for using ActiveMQ across multiple projects.

Utilizing Queues – PTP Messaging
As I stated previously, queue based messaging is always PTP; a producer sends a message to a queue and exactly one consumer will receive a copy of the message. For our API we will define a producer and a consumer of messages. First the producer:

This is simple class takes a session and a string identifying the destination or queue that we will be sending messages to as constructor arguments. Usage is even simpler, just call the SendMessage method and pass in a string to send. Note that this could be augmented to send more complex message types, but for simplicity I have omitted anything other than string messages.

The consumer class is likewise rather simple and has a constructor that takes the same two arguments, a session and a string identifier of the queue that messages will be received from:

The QueueReceiver requires that you register with a delegate that is fired when a message is received by the consumer. The client starts listening to the by calling the Start method and passing in a string that uniquely identifies the client. Like subscribers (and all other message consumers), the QueueReceiver should be a long-lived object, with a lifetime of the entire application.

The entire API, looks like the following:

Usage is very simple, provide a long-lived consumer object with a queue as its destination and then create shorter lived producer objects that send messages to the broker. The following unit test shows an example of the round-robin way that messages are received by the registered consumers of a queue:

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Cleaning up XmlWriter and IXmlSerializable with Extension Methods

by jmorris 4. November 2009 19:46

If you do any work with xml you probably have come across scenarios where you are using an XmlWriter to produce an output stream of xml. Eventually this output stream is either persisted to disk via an XDocument, sent over the wire using a distributed technology such as WCF, Remoting etc., or possibly transformed with XSL/XSLT. A strong example is custom serialization classes that implement IXmlSerializable.  For example:

The class above is a simple data transfer class (DTO) that implements IXmlSerializable so that it can be serialized and/or deserialized from an objet to an xml stream and vice versa. Note: in most cases you would simple mark the class as [Serializable] and/or provide attributes from the System.Xml namespace to provide the same behavior, however in many cases the default implemention will not fit your particular scenario, hence you would implement IXmlSeriable and provide your own custom serialization.

Here is the 'custom' serialization implementation:

While the XmlWriter/XmlReader API's are pretty simple to use, they are also a bit verbose. If you happen to have a fairly large class with many fields, things start to get ugly pretty fast. Typically when I see large classes, I began to think about refactoring into smaller classes when applicable, but that not always the case. Since, most of them time when want serialization/deserialization you simple want to quickly (i.e. less keystrokes) turn the contents and structure of the class into its xml equivalent you are looking at reducing the amount of work needed. This is where extension methods really come in handy:

The result compared to above is a much cleaner, easier to read class:

While extension methods are not new, they do offer unique way of handling situations where you would like to simplify a set of operations without reaching for the traditional static xxxUtil class or creating a customized implementation or wrapper class. In this case,  XmlWriter is a class open for extension via basic inheritance, unlike a sealed class such as System.String, which is the intended purpose of extension methods: extended classes closed to inheritance (sealed).

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Jeff Morris

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