While testing the downgrade functionality of one of our WiX-built MSIs, I have noticed something odd.
I have allowed downgrades in the MajorUpgrade element and I have scheduled that element to be afterInstallInitialize (but I have tried it thoroughly with afterInstallValidate and I experience the same problem; we can't have it after that action, but I thought I'd test it).
Many of the files (e.g. the DLLs in our Service's bin folder) are of a higher version, with each release; therefore, the version we are downgrading to includes files of a lower version. Yet all of those files are installed fine, during the downgrade, apart from the Service EXE files; further, the Services are also not installed in Windows.
Considering all of the above, after spending two days on this problem, and after much searching, I appear to be at a loss.
I have tried two things that seem to provide some hope:
1) I have tried setting the REINSTALLMODE property to amus. This ensures that the EXE files are installed, along with the Windows Services. But most things I read about that property warn against using it, and I even have to surpress ICE40, in order to get my package to build, when setting that property. This all concerns me, as I am not sure what negative effects could be missed, if I use this property in my MSI files.
2) When I remove the KeyPath attribute from the File elements that mark up the Service EXE files and place that attribute on the Component element instead, the Service EXE files are installed onto the system during the downgrade, but the Services are still not installed in Windows. After looking into this, it seems that the KeyPath attribute must be on the File element, if I'd like Services to be installed. So it seems to me as if this idea will not help.
Any help or advice would be very much appreciated. We really could do with providing downgrade functionality.
Thank you all for your time.
MSI is essentially opposed to the idea of downgrades. Once a file is on the machine, MSI tries very hard to keep the latest version of the file around as, among other reasons, downgrading the file can re-introduce a security vulnerability. I'd suggest not directly supporting downgrades; instead, you can show a message that tells the user to uninstall the higher version first.