Sunday, November 21, 2010

Shallow submodules in Git

A git submodule is really little more than an embedded repository with some configuration in the parent repository to track its HEAD. When you first clone the parent repository, you have to manually fetch the submodules by running:

git submodule init
git submodule update

This actually runs a clone (initially) for each submodule. Each submodule is a fully-fledged repository. You can even commit and push from a submodule repository (if you have permissions, of course).

But sometimes you only want submodules for read-only purposes. For example if you have a "superproject" whose purpose is to integrate several projects through submodules. When that's the case, it becomes annoying having to download the entire history for each submodule. It wastes time, bandwidth and disk for everyone that wants to work with this superproject. Shallow clones are great for this, but how can we apply them to submodules?

After asking on stackoverflow, Ryan Graham gave me the hint that "submodule update" can handle previously cloned submodules, so it was just a matter of running a "manual" shallow clone for each submodule between "submodule init" and "submodule update". This script does just that:

Keep in mind that the savings in disk space are usually not quite what you'd expect.

Wednesday, November 17, 2010

Windsor-managed MembershipProviders

I see many questions on Stackoverflow that are basically variants of this: "How can I integrate my custom MembershipProvider into my IoC container?"

Integrating your custom MembershipProvider to a IoC container has many advantages, since it would let you treat it just like any other service: you could manage its lifetime, dependencies, configuration, even proxy it if you wanted.

Problem is, MembershipProviders are one of those things that are managed by the ASP.NET runtime. You just configure it in your web.config and the runtime instantiates it when it's needed. You don't really get much control over its creation.

A cheap solution is to use the container as a service locator directly in your membership provider (using something like CommonServiceLocator), e.g.:

public class MyMembershipProvider : MembershipProvider {
    private IUserRepository repo {
        get { return ServiceLocator.Current.GetInstance<IUserRepository>(); }

    public override string GetUserNameByEmail(string email) {
        return repo.First(u => u.Email == email);


Using a service locator like this should be avoided as much as possible. Mark Seeman explains it thoroughly in this article. In a nutshell, you want to limit the usage of the service locator pattern to glue code (i.e. very low-level infrastracture), even there use it as little as possible, and never use it in application-level code.

As usual with this kind of problems, the solution is to write a wrapper/adapter/bridge/whatever-you-want-to-call-it that isolates the issue so that client code doesn't have to suffer it. It's similar in concept to the implementation of Windsor-managed HttpModules. It's actually simpler than that, we don't need a custom lifestyle manager here.

In fact, Spring.NET has had such an adapter for quite some time. The only problem with that implementation is that you can't change the lifetime of the custom provider, it's always a singleton. My implementation doesn't have this limitation: your provider can be transient, singleton, per web request, whatever. The price for this is that you can't use Initialize() (more precisely, it won't do anything), but since it's managed by the container, you can use the container to provide any configuration, which is much more flexible. The implementation is about 200 lines of boring, simple code so I'm not going to post it here. It does use Windsor as a service locator, but this is low-level infrastracture/glue code. The goal here is to keep your code clean.

The code is here, and here's how to use it:

  1. Write your custom MembershipProvider as a regular component, using constructor or property injection as you see fit.
  2. Implement IContainerAccessor in your global HttpApplication class. Use this article as reference.
  3. Register your custom provider in Windsor and assign a name to the component. E.g.:

  4. Register your custom provider in your web.config using the adapter and referencing the name of the corresponding Windsor component in a "providerId" attribute. E.g.:

        <membership defaultProvider="customProvider">
            <add name="customProvider" type="ProviderInjection.WebWindsorMembershipProvider, ProviderInjection" providerId="myProvider"/>

That's it. Here's a sample app that you can use as reference. This can be easily ported to any IoC container, and for any provider like RoleProvider, ProfileProvider, etc. I haven't used this in anger so let me know if you have any problems with it.

Tuesday, November 16, 2010

Migrating to FAKE

I finally finished migrating the SolrNet build scripts from MSBuild to FAKE. I did not do this out of a whim or just because I was bored, but because the MSBuild script was getting out of hand. At only 246 lines, it became unmaintainable. I admit I'm not a MSBuild expert, but a build script shouldn't be that hard. Just visually parsing the script was a daunting task.

This screenshot compares the FAKE and the equivalent MSBuild scripts side by side:


Even if you can't read it, I bet you can tell which is which.

XML-based DSLs like MSBuild and NAnt have only one advantage: being easily parsable by tools. But if you're going to do any sort of manual maintenance of the script, embedded DSLs in a real language will beat XML progamming every time.

I wrote the original build script for SolrNet in MSBuild for two reasons: no external dependencies, so it wouldn't place any burden on potential contributors; and being a NAnt user, I wanted to learn MSBuild.

But I should have known better: most of my NAnt scripts have evolved over the years to be mostly calls to MSBuild to compile solutions and embedded Boo to handle any logic.

Speaking of Boo, Phantom looks very nice. I picked FAKE over Phantom kind of arbitrarily, mostly because I'm really digging F# right now. But I'm keeping an eye on Phantom. Boo's macros and compiler extensibility are used in Phantom, and Boo's type inference and optional duck-typing make it an excellent language for a build system. And Boo is so small that you can fit the runtime and the compiler in under 2MB, so it's not an issue to distribute it.

Another option is Rake. Albacore and rake-dotnet implement the common .net-building tasks in Rake. But I really don't want to introduce a dependency on Ruby just to build the project.

Then there's PSake. PowerShell is quite powerful and I really like the concept of piping objects instead of lines of text as in unix shells. In the context of a build script, one of the main advantages of using a shell is that it's dead easy to call external programs, so "integrating" with ILMerge, Zip, etc is just a matter of calling the executable in question with the parameters you need, just as you would do it on the command line. No wrappers needed. And PowerShell is ubiquitous enough as to not consider it a dependency. But... I still can't get myself to like PowerShell's syntax. I know this is totally subjective, but I feel just like Jim here. Scripts involving .net are particularly ugly. And my first experience with PowerShell was bumpy to say the least.

Another (lesser for me) issue with PowerShell is that it currently doesn't run on Mono. It's not like I'm building SolrNet on Mono right now, but I certainly don't want to knowingly work against it.

So why did I pick FAKE and F# instead of all the others I mentioned?

  • F# is statically typed and has global type inference. If there is a type error in my script, it won't run. At the same time, type inference gives the code a scripty feel. I didn't have to declare a single type in the build script (you can see it here).
  • I can write my build script on VS2010, complete with intellisense, automatic error checking and debugging.
  • FAKE defines a simple, terse, functional EDSL to manage common build tasks.
  • FAKE is trivially extensible: just write a regular F# function (or .net method in any language) and invoke it. No particular structure or attributes needed. In just a few lines I defined some helper functions to manipulate XML and start/stop Solr to run integration tests.
  • F# works on Mono.
  • No external dependencies: F# is included in any default VS2010 install. And now that F# is Apache-licensed, it will soon be included in Mono (therefore also Ubuntu) and MonoDevelop.

I've also been contributing a few things to FAKE lately:

  • Enhancements to the MSBuild integration.
  • Enhancements to the ILMerge integration.
  • Gallio integration.
  • Simpler shell exec functions and some shell-like functions similar to Ruby's FileUtils.
  • A couple of bugfixes.

Bottom line: a few years ago all there was to build .net projects was MSBuild and NAnt. Nowadays there's a lot of choice. Make sure you do your research and pick the build system that's right for your project and for you.