Followup: Fix url alias migration on module install and uninstall

@railgun Thanks for the patch! I think we should use another approach when fixing this.

We shouldn't delete any entities from non-default workspace because of that is taking care the Workspace module, when that module is uninstalled, it deletes all non-default workspaces and entities associated with them. After that the url_alias table contains only aliases for entities on the default workspace.

We should fix this:
1. Make alias field unique, after uninstalling multiversion
2. Fix migration of the url aliases when entities are migrated back from the temporary storage on Multiversion uninstall. There is probably a way to not duplicate aliases, but replace or leave there those that already exist. If we make the alias filed unique it won't allow at all duplicate aliases and there will be an error when saving any duplicates - that is how it should work when Multiversion is not installed.

Explanation for 2.: when uninstalling Multiversion, it duplicates node url aliases because on migration it doesn't take into consideration already existing aliases into the database.

Steps to reproduce:

1. drush si -y
2. drush en deploy -y
3. Create 2 nodes with aliases on Live workspace, replicated them to Stage. Create a new workspace (Test), replicate all nodes from Stage to Test. At this point you'll see 4 entries in url_alias table.
4. drush pmu deploy -y
5. drush wun -y
6. drush repun -y
7. At this point in the url_alias table should be 2 entries - for the nodes from live, that's correct
8. drush mun -y
9. MUltiversion successfully uninstalled, but in the url_alias table are 4 entries, when the 2 nodes have been migrated back from temporary storage, they created new aliases in the database.

After deploying the 2 nodes to Stage and Test:

After uninstalling Workspace and before uninstalling Multiversion:

After uninstalling Multiversion:

@BAHbKA I see, when using drush mdt node -y command and Workspace module is not uninstalled then we can have multiple workspaces.

Truncating entity tables was an improvement and I don't like the idea of deleting again every entity from the non-default workspaces (as we try to do in #3)- this is a performance downgrade, if we do this, then our fix from #3048954: An alternative approach to including/excluding content types into "multi-versioning". was work in vain.

A solution would be on uninstall (after migrating entities to temporary storage and before migrating them back) to just loop through the url_alas table values and delete from there all the entries where we have as source /node/NODE_ID (maybe we have other possible cases?).

@BAHbKA You are right regarding, alias field not being unique, I got confused because I remembered that on node saving duplicate alias is not allowed, but that is restricted by the storage class, not database, sorry.

Will test the new solution I think it should work.

@BAHbKA Yes, that works, but I think it's still not the best solution. That because it creates unnecessary entries in the database, then we delete them. The best solution would be to control that on entity migration to multiversion/drupal storage, somewhere in a new process or destination plugin (Drupal\multiversion\Plugin\migrate\destination\EntityContentBase). On entity migration from the temporary storage it should do a check, if there exists already that alias, it shouldn't save a new one.

What do you think?

Thanks @BAHbKA! Will review it tomorrow morning.

@BAHbKA This works perfectly when uninstalling the module, but when installing the module it still deletes existing aliases and creates new ones (with new PIDs). Could we keep path aliases on module install and avoid deleting them and creating again (as we do on uninstall)?

@BAHbKA Fair enough, thanks! I'll commit this.

Thank you for the patch!

This patch should leave in another issue, not here, this is already fixed and the change is already in the latest module release. Please create a new issue, with a proper description and upload the patch there. This issue fixed the problem without Pathauto module installed. Thanks!