Copying indirectly referenced assembly to output d

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How does Copy-local work?

I have following situation:

• there's a project named OLAF.Tools, and that project references Microsoft.Data.SqlXml in C:\Program Files\SQLXML 4.0\bin\Microsoft.Data.SqlXml.dll. Reference Copy Local property is set to True. When I build that project in bin directory I can see both OLAF.Tools.dll and Microsoft.Data.SqlXml.dll
• there's a console application named OLAF.Generator, and that application references OLAF.Tools (I've added reference using Project tab). When I build that application in bin directory I can see only OLAF.Generator.exe and OLAF.Tools.dll - there's no Microsoft.Data.SqlXml.dll, what supprises me. Another wierd thing is that even though that dll is missing application is executing properly.

So my questions are:

• why Microsoft.Data.SqlXml.dll is not copied to bin folder of OLAF.Generator console application?
• how application resolves directory where Microsoft.Data.SqlXml.dll can be found?

Thanks,Pawel

EDIT 1: (after response from Marc Gravell)

@Marc Gravell: Your answer gave me food for thought, as I could swore that I could always see indirectly dependant assemblies in main application's bin directory. And IMHO I don't agree with you - with all due respect :)

Of course, references are not cascaded physically (we're are talking about strong relationship to classes, interfaces etc) - and it's exactly what I wanted to achieve when building OLAF.Tools library. That library provides a level of abstraction, it contains factories, and one factory accepts as a parameter string and returns interface. One particular implementation of that interface uses Microsoft.Data.SqlXml components. As a result, OLAF.Generator uses interface that is located in OLAF.Tools, but doesn't know about components in Microsoft.Data.SqlXml.

Apart from that (I think we both know what I tried to explain in preceding paragraph), when building application, dependant assemblies should be copied (if Copy Local is set to TRUE). I just wrote sample application, Project B lib has reference to Project A lib, and Project C (console app) has reference to Project B. In Project C's bin directory I can see all: Project A.dll, Project B.dll & Project C.exe. So in discussed scenario, the reason why Microsoft.Data.SqlXml doesn't end up in OLAF.Generator bin folder has something to do with that assembly itself.

Does compiler/visual studio knows that Microsoft.Data.SqlXml is located in directory which is automatically probed (or it's in GAC) and this is the reason why that assembly is not copied?

EDIT 2: I've just checked GAC, and indeed, Microsoft.Data.SqlXml.dll is installed in GAC.

Answer 1

How does Copy-local work? log4net.dll is not being copied to MyProject output directory - this is answer to my question. When library is installed in GAC, it won't be copied even though COPY LOCAL setting is used.

Answer 2

References are not automatically cascaded, so adding a reference to OLAF.Tools does not also add a reference to SQLXML. If you want to deploy SQLXML with your exe, then the most convenient way to do that is to explicitly add a reference to SQLXML from your exe, and set it to copy local. Without this, it is not deployed. Basically, the onus is on the developer to decide which files are actually needed at runtime (which is often a subset of the references used, and depends on a number of deployment decisions which only you can know).

Re how it is resolved at runtime... the probing paths are a bit of a black art, mainly meaning "the app folder", but it depends on the config, and indeed the GAC may be consulted. You also get an opportunity to provide your own resolver, via AppDomain.Current.AssemblyResolve.