CODEWITHSUNDEEP
unity-containeraopunity-interception
telewin
telewin

Reputation: 1122

Is interception worth the overhead it creates?

I'm in the middle of a significant effort to introduce NHibernate into our code base. I figured I would have to use some kind of a DI container, so I can inject dependencies into the entities I load from the database. I chose Unity as that container.

I'm considering using Unity's interception mechanism to add a transaction aspect to my code, so I can do e.g. the following:

class SomeService
{
    [Transaction]
    public void DoSomething(CustomerId id)
    {
        Customer c = CustomerRepository.LoadCustomer(id);
        c.DoSomething();
    }
}

and the [Transaction] handler will take care of creating a session and a transaction, committing the transaction (or rolling back on exception), etc.

I'm concerned that using this kind of interception will bind me to using Unity pretty much everywhere in the code. If I introduce aspects in this manner, then I must never, ever call new SomeService(), or I will get a service that doesn't have transactions. While this is acceptable in production code, it seems too much overhead in tests. For example, I would have to convert this:

void TestMethod()
{
    MockDependency dependency = new MockDependency();
    dependency.SetupForTest();
    var service = SomeService(dependency);
    service.DoSomething();
}

into this:

void TestMethod()
{
    unityContainer.RegisterType<MockDependency>();
    unityContainer.RegisterType<IDependency, MockDependency>();

    MockDependency dependency = unityContainer.Resolve<MockDependency>();
    dependency.SetupForTest();
    var service = unityContainer.Resolve<SomeService>();
    service.DoSomething();
}

This adds 2 lines for each mock object that I'm using, which leads to quite a bit of code (our tests use a lot of stateful mocks, so it is not uncommon for a test class to have 5-8 mock objects, and sometimes more.)

I don't think standalone injection would help here: I have to set up injection for every class that I use in the tests, because it's possible for aspects to be added to a class after the test is written.

Now, if I drop the use of interception I'll end up with:

class SomeService
{
    public void DoSomething(CustomerId id)
    {
        Transaction.Run(
            () => {
                Customer c = CustomerRepository.LoadCustomer(id);
                c.DoSomething();
             });
    }
}

which is admittedly not as nice, but doesn't seem that bad either.

I can even set up my own poor man's interception:

class SomeService
{
    [Transaction]
    public void DoSomething(CustomerId id)
    {
        Interceptor.Intercept(
            MethodInfo.GetCurrentMethod(),
            () => {
                Customer c = CustomerRepository.LoadCustomer(id);
                c.DoSomething();
             });
    }
}

and then my interceptor can process the attributes for the class, but I can still instantiate the class using new and not worry about losing functionality.

Is there a better way of using Unity interception, that doesn't force me to always use it for instantiating my objects?

Upvotes: 3

Views: 569

Answers (1)

Samuel Neff
Samuel Neff

Reputation: 74909

If you want to use AOP but are concerned abut Unity then I would recommend you check out PostSharp. That implements AOP as a post-compile check but has no changes on how you use the code at runtime.

http://www.sharpcrafters.com/

They have a free community edition that has a good feature set, as well as professional and enterprise versions that have significantly enhanced feature sets.

Upvotes: 0

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