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    <p>Dependency Injection tends to use a concept known as a composition root. This is a single place in your application where the composition of the object graphs for your application take place.</p> <p>You do not use a dependency injection container in a library, per se. Your library may include objects that can be injected, but it tends to be an application based tool, not a library based tool.</p> <p>What this means is that if you are creating a library only, you would not use a dependency injection container in it, or configure a container in it. Instead, you would create your library to work with dependency injection from your application. In your case, you would simply design your Repository, Unit of Work, etc.. to accept its dependencies via constructor injection. Then, in your application that uses your library you would use a DI container (such as Ninject) to configure how objects get created.</p> <p>This does a number of things. First, it allows the application to control how objects are created. For instance, if you're using your library in a web app, then you can configure it to create an instance of your repository that lives for the life of one request. If your library did this, then you would have no control over this at the application level.</p> <p>Second, if you use a DI container in your library, then you would also need a DI container in your app, thus you would end up with two DI containers, and that could cause various conflicts. There should only be one DI container in an application in most cases.</p> <p>Finally, you are committing a classic newbie blunder. You are confusing the DI container, with the concepts of DI itself. DI is the way in which you design your classes, in particular how they accept dependencies from outside the objects.</p> <p>A DI Container is a tool used to achieve DI, not DI in and of itself.</p> <p>TL;DR</p> <p>Do not design libraries to have their own DI container. </p>
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    1. PONinject EF4, Repository and Unit of Work
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    1. USErik Funkenbusch
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    1. COHi, I think you are saying I should design my data class library as I normally would then maybe derive my unitofwork from an interface. Then in my application, I could configure the IoC container to inject a concrete implementation of my Unit of work, obviously my test unit of work would derive the same interface and the DI container could inject a test unit of work instance in my unit tests. If this is what you mean and I don't sound like I am babbling then thanks makes alot of sense. If I do sound like I am babbling then maybe I misunderstand you and I'll be happy if you correct me. Thanks
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    2. CO@ObiOnuorah - Yes, sort of. It really depends on whether or not your library is intended to be genericly used, or only intended for use in this one (or a small set of) application(s). If it's intended to be generic, then I would not suggest any design that is dependent upon dependency injection. But, if it's only intended for use in your applications then you can control the DI that's used. In any event, a DI container should be implemented at the application level, but your libraries can use the DI philosophy in their design (ie designed to use constructor injection).
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