In the previous post, we introduced ExportFactory<T> and demonstrated how it can be used to control the lifetimes of MEF parts. In this article we will talk about a new type MEF called CompositionScopeDefinition that can be used in conjunction with ExportFactory<T> to control sharing. Let’s take a scenario that we could not achieve using what we know currently and how CompositionScopeDefinition provides the needed control. Important note: CompositionScopeDefinition is geared towards more advanced, desktop application scenarios. If you're using MEF in an ASP.NET MVC web application and want to control sharing and lifetime on a per-HTTP-request level, you should use the pre-defined ASP.NET MVC integration. Lets go back to our application block diagram that we built in Part 1 of this article.
Now let’s add a few details to this architecture. As our application has grown more complex, we have decided to factor out the data access part into a separate component called DataAccessLayer, which handles manages the connection to the database and reading and writing to it. In addition to this we also want to add a logger, which also logs some tracking information to the same database. So our slightly expanded functional diagram looks like the following. Read more: BCL Team Blog
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