如何动态加载引用同一程序集不同版本的DLL？

Question

We need to run sequentially database updates. Each database update will be its own DLL, and needs to retain a dependency on a specific version of our Domain DLL (the current one at the time the update was written). For example:

Cool.Program.Update0001.dll is dependent on Cool.Program.Domain.dll version 1.0.1
Cool.Program.Update0002.dll is dependent on Cool.Program.Domain.dll version 1.0.3
Cool.Program.Update0003.dll is dependent on Cool.Program.Domain.dll version 1.1.6

My plan is to store these DLLs & their dependency DLLs in sub folders as follows:

%APP%\Cool\Program\Updates\0001\Cool.Program.Update0001.dll
%APP%\Cool\Program\Updates\0001\Cool.Program.Domain.dll   (version 1.0.1)

%APP%\Cool\Program\Updates\0002\Cool.Program.Update0002.dll
%APP%\Cool\Program\Updates\0002\Cool.Program.Domain.dll   (version 1.0.3)

%APP%\Cool\Program\Updates\0003\Cool.Program.Update0003.dll
%APP%\Cool\Program\Updates\0003\Cool.Program.Domain.dll   (version 1.1.6)

Then have my main program load & call each Update DLL in sequence, dynamically, using reflection:

var path = System.IO.Path.GetDirectoryName(typeof(this).Assembly.Location) + "\\Updates\\" + versionNumber + "\\Cool.Program.Update" + versionNumber + ".dll";
var assembly = System.Reflection.Assembly.LoadFile(path);
var type = assembly.GetTypes().First(x => x.Name == "Updater");
var method = type.GetMethod("DoYourThing");
var result = method.Invoke(null, dbConnection) as string;

Unfortunately, having tested this design and interrogating the version numbers, I find that each UpdateXXXX.dll is working with the LATEST Domain.dll, even though an earlier one is stored in its own subfolder. I assume that they are resolving their dependencies through the GAC, or, defaulting to the dependency already loaded in the main program. (BTW I see in Visual Studio that it is not possible to force "Specific version" for a project reference and a quick google-fu suggests this isn't straightforward.)

My question:

How can I force the Update assembly to resolve its dependency on the Domain dll to its local folder?

Or:

Can I explicitly inject a dependency for a dynamically loaded assembly?

EDIT: I've found an answer, see below.

Answer 1

I'll answer my own question as I have completed it in the mean time.

This code does the trick:

// versionNumber = "0001", "0002" etc

var basePath = Path.GetDirectoryName(typeof(this).Assembly.Location) + "\\Updates\\" + versionNumber + "\\";
var updateAssemblyPath = Path.Combine(basePath, "Cool.Program.Update" + versionNumber + ".dll");

var setup = AppDomain.CurrentDomain.SetupInformation;
setup.ApplicationBase = basePath;
var newDomain = AppDomain.CreateDomain("Updater for " + versionNumber, null, setup);

var obj = (ICanDoSomething)newDomain.CreateInstanceFromAndUnwrap(updateAssemblyPath, "TestDynamicAssemblyLoading.Update"+ versionNumber + ".Class1");
var result = obj.TellMeYourVersionsAndDependencyVersions();
MessageBox.Show(result);

It assumes that the class being used implements a known interface (eg. "ICanDoSomething") and inherits from MarshalByRefObject:

public class Class1 : MarshalByRefObject, ICanDoSomething
{
    public string TellMeYourVersionsAndDependencyVersions()
    {
        return
            typeof(Class1).Assembly.GetName().Version + "\n\n" +
            "My reference to Domain\n=================\n " + SomeModel.TellMeYourVersionsAndDependencyVersions() + "\n\n" +
            "My reference to Common\n=================\n " + SomeUtility.TellMeYourVersion();
    }
}