We can help you get your Mx 7 version back. Please submit a support ticket here:
Use “Incident” in the drop down “Please choose your issue below” and fill in the form with your details and the App ID that you can find in the Mendix Developer Portal page for your app under the left navigation menu item at the bottom that says “Settings” and then subitem “General”. Scroll down to see your App ID.
Please also refer to this forum post, so you don't have to repeat yourself and we can quickly find the context of this issue. We will get in touch with you to once we have investigated the app status and discuss with you what best to do to help you restore your demo app in the desired state.
Best Regards, Koert
You can reverse that commit that upgraded your project. In the past this would be done with tortoise svn 1.7. The steps to do so can be found here. Since you upgraded to the Mx8 beta on accident the new subversion is 1.9 ( as mentioned here), you can either install smartSVN and try to figure out the same steps to revert a commit, or you can uninstall tortoise svn 1.7 (if its installed) and install tortoise svn 1.9 (in hopes the stesp are similat to version 1.7). You can also try contacting support to get the steps to revert a commit in subversion 1.9.
Hope this helps!
Given it is a demo project you could also make it easy for yourself and branch of from the commit right before you upgraded.
Read this on how to make branches:
https://docs.mendix.com/refguide/create-branch-line-dialog you will need to do this from the Mendix Studio Pro. If you have an old working copy that is still to be opened in 7 you can use that to create the new branch. Otherwise you will need to download beta 8 create the branch (do not download it!). Open Mendix 7 open the app (switch the branch) and voila. Now you can continue your work on that branch.
If you want you could even overwrite the mainline with the code from the working copy (copy everything except the hidden SVN folder https://support.microsoft.com/en-us/help/4028316/windows-view-hidden-files-and-folders-in-windows-10) from the branch folder into the mainline folder (before you do delete everything except the hidden svn folder). And then commit, you just downgraded to Mx 7.
I would like to thank everybody for their response. Luckily the application was a demo application so no harm no foul. I am glad others have investigated this issue and concluded that it was probaly a one time error.
I have downloaded Mendix Studio and started developing using that application. I would advise everybody to use Mendix modeler instead of the online editor. Especially the ability ti use version control is very helpful.