Entity Framework generic repository life cycle

I've read a couple of articles about creating a generic repository in Entity Framework. In every article the Objec开发者_运维问答tContext is passed as an argument to the constructor like this:

public Repository(ObjectContext context)
{
    _context = context;
}

In a web application the preferred way to handle ObjectContext lifestyle is per web request. This means that these repositories must also have lifestyle per web request, if used in in a web context. This spreads to services using repositories and further on if we stick to constructor injection...

I think the ObjectContext life cycle should be handled outside the repositories, for example in a HttpModule. I would also like to handle repositories as singletons instead, and then ObjectContext can't be injected in the constructor. Another mechanism for getting the ObjectContext into the repository must be used, like an ObjectContextFactory.

Whats the downside of handling the repositories with a singleton lifestyle?

One issue with repositories being singletons, as with any other objects, is that determining what dependencies the repository has becomes more difficult. When you require that a context is passed in the constructor that is a clear declaration of a dependency on the ObjectContext class. If you were to use a static factory to get a reference to an object context then it would be necessary to see the implementation of the repository to know how it uses the factory.

A common way to achieve what you're looking for, namely the ability to manage the scope of the ObjectContext class outside of the repository is by using a dependency injection library, such as Autofac. You can register the ObjectContext class such that a new instance is created for every HTTP request. Then if you also register the repository class, when a repository is requested the dependency injection container will attempt to get a reference to the ObjectContext dependency. Since only one instance of ObjectContext will be created per HTTP request multiple repositories within that scope will receive the same instance. The Autofac page has example of integrating with ASP.NET that you can look at.