Posts tagged with 'IoC'

In a project that I'm working on, I'm using Dapper for data access and I'm using StructureMap as my IoC containter. It's an ASP.NET MVC project.

I was recently demoing the project to my partner on the staging site (Azure), and I ran into a troubling error having to do with data connections (that I had not experienced running it locally on IIS yet). I immediately thought that it must be an issue with the SQL connections (SqlDbConnection objects that implement the IDbConnection interface, per Dapper) not being closed and/or disposed of correctly.

I remember encountering the same issue when I was developing this very site that you are reading, and the solution is to use the HttpContext scope within StructureMap when configuring it for the IDbConnection interface.

Here's what I started with:

And here's what I refactored it to:

I just added HttpContextScoped (the default is PerRequest scope, see StructureMap docs on Scoping and Lifecycle Management). I also added the ReleaseAndDisposeAllHttpScopedObjects to Global.asax.cs, so that StructureMap would...release and dispose those objects at the end of each request.

However, when I did that, I was still getting problems. I would get exceptions saying that the SqlConnection ConnectionString was the empty string. Something wasn't right. I did some searching around about the issue in the docs, and couldn't really find what I was looking for. I did come across someone with a similar issue on StackOverflow, also trying to understand HttpContextScoped. The top answer from PHeiberg (not the accepted answer) pointed me the right direction.

I used a lambda expression instead of just passing the SqlConnection directly. So now my SqlDbConnections are scoped to the HttpContext, and will be cleaned up after every request. That should squash the issue I was seeing on the staging stie.

Ack, WebForms! Burn it with fire!

WebForms is known to be a horrible ghetto full of HTML pitfalls, a Kafka-esque lifecycle, testability nightmares, and pages served up with inflated ViewState data.

Some of that is still true, but WebForms has improved, and despite all the horrors that we're familiar with, it's still got a lot going for it, including a control tree that can be very useful at times.

I have been working on a WebForms project in my independent consulting practice (it sounds so fancy when I say it like that). Even though it's a relatively small project, I was still thinking about how best to introduce dependency inversion [PDF] to the project (or if I even should).

I googled around, sifted through a lot of ancient blog posts, and I came up with a relatively simple solution with my favorite IoC tool, StructureMap. It's not really optimal, or terribly elegant, but it just might get the job done and still allow us to write tests. I'm certainly open to alternatives, but because this is a small project, I don't want to spend a ton of billable hours on a solution, especially when I'll be turning the code over to novice programmer(s) when my time is done.

First, I simply add standard StructureMap config to the project. Application_Start in Global.asax is as good a place as any. I also use the default convention (if you aren't familiar, it's basically naming the interface by prepending an "I" to the concrete class name).

Okay, so that's pretty standard. Now let's approach from the other end: an actual code-behind class of an ASPX page. I can't use constructor injection here, because I don't have much control over this object being instantiated. Instead, I'll just make public properties for my service(s).

So now I've got a StructureMap defintion, and I've got properties that want to be set by StructureMap. But how do I get them talking? My solution was to introduce a base class (bleck) to the WebForms page. In this constructor, I'll use StructureMap's BuildUp method to populate properties (I have to specify which ones, as noted later on).

That's the ugliest part, as far as I'm concerned, but I couldn't think of a better solution. Maybe an HttpModule or something? Maybe the newer WebForms releases contain something that I'm not familar with yet? Leave a comment with your suggestions.

Finally, StructureMap just won't go and set every property by itself. You need to specify which ones. There are a couple of ways to do this. One is the SetAllProperties, which allows you to conditionally examine the PropertyInfo, and the other is FillAllPropertiesOfType, which you can use to directly specify which properties to set based on what type they are. Even though it's a small project, I'd would prefer to use SetAllProperties, so I don't have to go back and edit my StructureMap config each time I create a new service or a new WebForms page.

Here's a quick example of how to write a caching aspect with Castle DynamicProxy.

First, let's write an implementation and a service worth caching:

Next, you need to decide where to cache the results. If you're using a web app, maybe try ASP.NET's Cache object. If you're writing an Azure app, try AppFabric caching. You can cache things in a database, a text file, whatever is appropriate for your application.

For this simple example, I'm going to cache everything in memory, in a static Dictionary object. Also, nothing that goes into my cache will ever expire or be invalidated. Once it's cached, it's cached forever. Also, it's not thread safe. Not a very useful cache in a real app, so let me just be clear: do not use this in a production application. It's only for demonstration: whatever you use for caching is up to you, I'm just demonstrating the aspect part.

I'm generating the cache key by appending the argument values to the method name. So if you call MyMethod("test") and MyMethod("test2"), that's two different keys that will cache two different results. This might work for you, or you might need a more complex GenerateCacheKey method (something that uniquely identifies objects, perhaps).

Next, I wire up my IoC container to return MyService when asked for an implementation of IMyService. But I also have to make sure that my IoC container (StructureMap in this case) applies the caching interceptor to it.

I put it all together in a simple console app:

And here's the result:

Console app with caching

Do you agree with these concepts?

TDD is great, BDD is better. DDD is the way it should be done. SOLID principles should always be followed. Don't repeat yourself. Be agile. Follow the boy scout rule. Use an IoC tool and/or dependency injection. Don't reinvent the wheel. Always normalize your SQL tables. Use AOP to avoid boilerplate and clutter.

I do. And a lot of other people do too. But why? Because:

  • ...it's been drilled into your head by peers and at software conferences?
  • ...you have baggage from a previous job or hate your current job?
  • ...you read about them all in a book like Clean Code, and assumed Uncle Bob knows what he's talking about?

Or have you actually researched and practiced each of these concepts and found them to be superior in many cases to the alternatives (which you've also researched and practiced)?

Well, for me, the answer is: all of the above. Except I don't hate my (current) job.

Yes, I just admitted that I've blindly subscribed to a lot of the tenets that you probably hold dear because of peer pressure and authority figures. This isn't necessarily a bad idea: authority figures and peer pressure can be useful constructs. But independent of your own healthy skepticism and critical thought, they can be dangerous too.

So before you run with any new acronym like BDD or AOP, do your research: see what your peers think, see what authority figures think, and finally use your own brain to put it all together.

One of my favorite acronyms is "RTRJ" for "Right Tool for the Right Job". At worst, it's something of a cliche, and sometimes even an excuse or blanket answer. But I think it's an important thing to keep in mind whenever you are thinking about architecture of an application. If there was a perfect framework or tool for every job, then architecture would be easy because then every developer would always be on the same page.

I came across this article on CodeProject about making architectural decisions and choosing technologies for a .NET project. While you may not agree with every choice made for that project just from reading, I think it's interesting and important to note why each decision was made. For instance, the author was looking at IoC/AOP tools for the project, and considered many popular tools like Spring.NET, LinFu, and PostSharp. Ultimately, the author determined that Spring.NET was the best choice because of its documentation, integration with NHibernate, and the fact that it also comes with dependency injection capabilities. The author also notes the downsides and risks to using Spring.NET.

I think "Right Tool for the Right Job" consists of two main concepts: understanding the job and choosing the right tools. Everyone can probably rattle off their favorite tools, but are all of those tools correct for this project?

  • Is the rest of the team more familiar with and comfortable with a different tool?
  • Will this project be cheaper or faster to finish with a certain tool?
  • What about support: is an older tool with a bigger support community better than a newer tool that doesn't have a big following yet?
  • Are the benefits of new tool going to outweigh the uphill challenge of learning curves and convincing others to adopt it?
  • Biases: even if you don't admit you have them, you have them. Figure out a good way to make your analysis objective: have others on the team do the spike and get their opinions. Try to play devil's advocate. Find someone to ask you the hard questions and find the answers.
  • Is tool X being used just because it's always been used before? There's probably a good reason for that, but don't be afraid to challenge assumptions and the status quo, even if it does end up being quo.

Above all, don't forget: shipping is a feature. You could spend eternity trying to figure out just the perfect combination of tools and architecture, but ultimately the best way to get feedback is to get building! If you find yourself putting a square peg in a round hole during your first sprint (I'm assuming you are using some sort of agile methodology), say so at your retrospective and switch to something else while you still can.

Matthew D. Groves

About the Author

Matthew D. Groves lives in Central Ohio. He works remotely, loves to code, and is a Microsoft MVP.

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