Why contract first

This means you need to map the single messages to operations inside an interface. This phase is obviously the most tedious to complete. Whereas tool support for XSD is extremely good for.

In order to get started using the WSDL Wizard you need to add the two existing XSD files for the data and the message types to your contract metadata project. Based on the messages you have designed, you now want to set up the interface. You just have to right-click on the UgMessages. On the following page the user has to provide some basic information about the interface including the name, XML namespace and an optional comment. The next page in the wizard allows you to add additional message XML Schema files.

Because sometimes you can start right away with one file, but actually have different kinds of message types distributed across several XSD files see Figure 5. Now on to the real meat. Page three of the WSDL Wizard offers a listview component that allows you to add the interface's operations. But this is not enough information to complete this step. There needs to be an explicit configuration of the message exchange pattern MEP to employ for each operation.

The former expresses that this is a one-shot action, which means you do not want any message sent back to the original sender. The latter indicates that there has to be an answer to the request message Figure 6. If you are following certain naming patterns for the modeled messages, the wizard will be able to infer the operations from the messages.

You're nearly done. The last important step lets you specify the operation's message parameters. On this page the user simply needs to map the appropriate message from the message XSD files to the message part of each operation. If you were using operation inference in the previous step the wizard has already set the right values here. Optionally, you can also set any number of message headers on this wizard page. Message headers accord to SOAP headers and you can use them to communicate out-of-band data and information like security credentials or transaction IDs Figure 7.

Although there are still some options on the last page of the wizard, you normally do not need them. That's it! Now you should have all the necessary data to actually get the service interface description generated by the tool.

A more thorough look at the generated WSDL Listing 3 unearths a small but very powerful implementation detail. The message schemas are not embedded in the WSDL but rather just imported.

This approach has several advantages. The most obvious one is reusability and the second most obvious is that it lets you independently work on the message schemas and the interface contract. So you can easily use or re-use already existing schema for your service's messages. All in all this makes three important metadata files. Both the Web service implementer as well as the client programmer will now need to receive the UGData. You can add all three files to the respective projects for the Web service and the Windows Forms client application.

Now you can head into the code generation process. The first big phase is over. It is now time to get to the real code. You'll need to create a CLS-compliant representation of the data, message, and interface contract. Sure, you could use wsdl. But there are two major caveats: it is not fully integrated into the IDE although there is the infamous Add Web Reference NET code.

What does "good" code mean in this context? There are several factors for. NET code that gets generated from metadata. First, you should have an option that allows you to generate runtime serializable classes. Second, it is indispensable to have not just public fields in your data classes that get generated from the XSD data contract. Rather, you need a good OO style here that is reflected by having private fields and public properties.

At least those two features are not present in. NET Framework 1. But the other strong side of WSCF provides an enhanced code generation engine that does not only fulfill these two requests. A developer can choose to either use the command line tool wscf. NET to smoothly stay inside their beloved development environment. For the purpose of this article I'll use the graphical add-in. In order to see how code generation works with WSCF it is time to think like a Web service developer.

The code generation process for the client application is analogous. Figure 9 allows you to select different options for code generation. You will choose all of them in order to get a fully fledged. NET representation of your data, message, and interface contract. After you've finished generating code you'll see a number of files added to the Web services project Figure Let's take a look at each feature that WSCF provides in respect to code generation.

The first important fact to note is that WSCF exclusively works with. NET interfaces. It generates a. NET interface instead of the abstract class with all the unnecessary and duplicated ASMX attribute glue that gets spit out by tools like wsdl. This approach is extremely helpful if you want to separately host the service interface and the service implementation.

In this case you have to define a shared interface that follows the same contract as the WSDL file. The tool also generates an interface for the consumer-side proxy if you choose to create a Web service proxy.

You can imagine that this easily enables scenarios where the proxy generation and instantiation can be done by a configurable factory. By doing so you can hide the location and the chosen transport. The second obvious feature is that WSCF can optionally create separate files for all data, message, and interface contract artifacts. All the types live inside the very same.

NET namespace. This way a developer can easily just delete or exchange one or the other type by eliminating the file. This is sometimes useful because you might happen to have another, better implementation for example, for UgMember, in your enterprise- or project-wide types library that you would use rather than the one generated from the data contract.

If you dive into programming the Web service logic you'll discover another nice feature of the generated code. Each type has a default constructor with all necessary initialization parameters already in place.

So if you want to wire up a sample implementation for the GetMemberData operation, you might proceed like the following please consider the completely message-oriented programming model.

This makes it very easy to embrace the message-based programming model without the need to write many lines of code. But often this is just too much burden for the runtime to take. You might want to have the chance to validate the incoming and also the outgoing SOAP messages against the message and data schemas you already have in place.

WSCF can optionally provide this feature for Web service implementations. When choosing this option it adds an external assembly to the project and implements a SoapExtension for handling all the schema validation logic.

Last but not least, you need an easy way to basically test your Web service. The ASMX runtime provides a documentation and help page for this purpose. But the problem with the default page is that you still might call? WSCF takes the route that it adds a new custom help page that looks and feels like the original one but disables the? Because in the contract-first world you start from the WSDL, you do not want to have the WSDL available through the endpoint although it would be technically possible.

For the sake of a complete overview of the sample scenario in this article, it will help to also take a look at the Windows Forms client application. All in all things look quite similar on the client compared to the Web service itself. The same class files get generated except that you now have a WebServiceProxy instead of a WebService type, but this is an obvious difference.

Likewise, you can easily write code that has a sample call to your Web service on the other side. The following snippet shows how to create a message-oriented call to the service's GetMemberData operation. Did you notice the last line? The result data object is directly bound to a Windows Forms PropertyGrid control Figure 11 -you didn't have to manually hack anything. This is possible because WSCF offers all the necessary attribute glue for it if you enable the appropriate code generation option.

Another interesting point to discuss about the client is the ability to get read-only access to the SOAP request and response messages. It's not a big deal and there are not a lot of people who will ever need it, but I've heard of customers who complained about this features missing in the original. NET Framework implementation. Now you're done with your application scenario.

You've modeled your data and your messages to exchange with XSD. Finally, you provided the respective developers with the necessary metadata and they could get along with WSCF's code generation feature to create code from the XSDs and the WSDL - in a much more enhanced fashion than it is currently available in the.

But honestly, there is never just one shot you never make everything just right the first time. Therefore it is indispensable to provide a round-tripping functionality for WSDL interface descriptions.

Just imagine you've forgotten to add an operation for enumerating all registered members. This means that you need to add the ListAllMembers operation to the interface. Figure The wizard starts and pre-populates the pages with the metadata from the WSDL. From now on you can change about anything you like, including adding and removing operations and changing the mapping of operations and message types. That's it: a complete contract-first design and development lifecycle.

What did you think about Web Services as described by this article? Sure, this is just one valid point of view. You can still think and act in an RPC-fashioned manner, no problem. But when you are serious about interoperability and integration, I think you should at least take a look at contract-first design and development when it comes to Web services. We are heading slowly towards maturing the Web services specs and features.

Microsoft's Indigo run time and programming model will provide us with some very rich and powerful features regarding building distributed systems, especially with focus on the Web services world. With contract-first-based ideas you're also well shaped for the near future. Indigo e. These concepts should by now be quite familiar to you. So the future is bright, start to use it now.

Please note that this article comes with a beta version of WSCF 0. The final version should be available for download when you read this article, however. If there are any questions, problems or suggestions regarding contract-first design and development, please do not hesitate to contact me. Contract-First Development is about making your intent clear across team members, external teams or 3-party systems.

We also update the "contract" before we implement changes to the code. Further benefits include:. So that everyone can be productive in parallel AND we can have strong guarantees of the resulting applications working together properly.

Instead of UI development being blocked awaiting a working service to code against, UI and Service developers can work in parallel. Also, if you define the contract first when developing or changing API interfaces, you have a clearer "Definition of Done" and "Acceptance Criteria" for the work. Check out these great links which can help you dive a little deeper into running the Contract-First Development practice with your team, customers or stakeholders. Improve this answer. Dousti 3, 6 6 gold badges 32 32 silver badges 45 45 bronze badges.

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