This registry will be created on application start up and will contain all objects of type FilterBase. Later we’ll add the ability for the registry to load assemblies from a share, so that you can add other filters as simple plugins. Information about each filter retained in a class FilterDefinition, and the FilterRegistry is merely a glorified List of the FilterDefintions. When we want to create a pipeline of filters we will want to instantiate new copies.
Using Expressions we can create Functions that will be stored with with our definition for each filter type. Here is FilterDefinition: We’ll invoke the compiled delegate at runtime to create our filter. The method AddCreateFilter handles this: FilterRegistry is meant to be run once at start up so that all filters are registered and ready to use. You can imagine how slow it could become if every time you process a Workflow Step that you must interrogate all the assemblies. Once you FilterRegistry has all assemblies registered you can query and create new combinations with the method GetFilters: Pipeline can accept a list of filters along with the string that represents the order of execution. The method RegisterFrom accepts a reference to the FilterRegistry along with the names of the filters you want to use. In the case of the Workflow Processor, we need to divide our filters into pre-trigger and post-trigger activities.
Referring back to our 5 questions that our processor asks, question 1 – 3 must be answered before we attempt to transition the Workflow State, while steps 4-5 must be answered after the transition has succeeded. The method ConfigurePipeline in WorkflowProcessor.cs accomplishes this task: Putting It all Together. A lot of talk and theory, so how does this all fit together? The test class WorkflowScenarioTests illustrates how our processor works. We are creating a workflow that implements the process for a Red Shirt requesting a promotion off a landing party. You may recall that the dude wearing the red shirt usually got killed with in the first few minutes of Star Trek, so this workflow will help those poor saps get off the death list. The configuration for the Workflow is contained within the file RedShirtPromotion.json. There are a few simple rules that we want to enforce with the Workflow. For one, Spock must review the Red Shirt request, but Kirk will have the final say. Here is a sample from the class WorkflowScenarioTests.cs: Study the tests. We’ve covered a lot together and admittedly there is a lot swallow in this post. In our next episode we’ll look at how to the Pipe and Filter pattern can help us with extending our workflow processor’s capability without causing us a lot of pain. Enjoy and check back soon for our next installment. Sensei will let you take it on out with this groovy theme (click play). Todd Herman Allen Jones Matthew MacDonald Rakesh Rajan. Instant download Readable on all devices Own it forever Local sales tax included if applicable. Sometimes you just need to solve a problem and get on with your work. To that end, Visual Basic 2008 Recipes is a compendium of practical solutions for busy VB .NET programmers. Create time for the more interesting aspects of your VB .NET project by solving common problems with the practical solutions and dozens of code examples in this book. Important .NET 3.5 technologies, such as Windows Presentation Framework (WPF) and Language Integrated Query (LINQ), are covered, and each chapter addresses a specific problem domain, including database access, multimedia, XML manipulation, networking, and security.
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