Is it “safe” to cache IServiceProvider for an app's lifetime?

Question

I\'m using ASP.NET Core, and its builtin DI container. I\'m using a third-party library (NLog) which I can\'t change.

My Foo class has a dependency (by

Answer 1

You don't want to inject your IoC container anywhere. That's a bad practice that allows for sloppy coding, and makes unit testing harder, amongst many other reasons.

Instead introduce a factory that can be injected and create a context on demand:

public interface IDbContextFactory<TContext>
{
    TContext Create();
}

public class DbContextFactory<TContext> : IDbContextFactory<TContext>
    where TContext : DbContext
{
    private readonly Func<TContext> _contextCreator;

    public DbContextFactory(Func<TContext> contextCreator)
    {
        _contextCreator = contextCreator;
    }

    public TContext Create()
    {
        return _contextCreator();
    }
}

Now if you inject this into your Foo:

public class Foo 
{
    private readonly IDbContextFactory<MyContext> _contextFactory;
    public Foo(IDbContextFactory<MyContext> contextFactory)
    { 
        _contextFactory = contextFactory;
    }

    public void bar() {
    {
        using (var context = _contextFactory.Create())
        {
            // use your freshly instantiated context
        }
    }
}

Any decent dependency injection framework can resolve the Func<TContext> parameter of the DbContextFactory, and pass a func there that creates an instance per request.

Answer 2

Addendum to @CodeCaster's excellent solution.

It's important to change Func<Dependency> to Func<Owned<Dependency>>. Otherwise the container won't return new instances each time, even though you're using a delegate factory.

Probably has something to do with the fact that a long-lived component (singleton) depends on a short-lived component (per-transaction). The Func<> prevents the captive dependency bug, but for the factory to also give you new instances each time, it needs to be Owned<>.

I don't understand why, and it seems counter-intuitive, but that's how it works.