Pitfall in Drupal 7 to Drupal 8 Migration
Issue: Migrated roles is not showing properly in user edit page.
Solution: Roles are migrated but not visible in the front end (user/%/edit page) because the user's language is not set. A custom script was written to set the language for the users.
2. Filter format configuration
Issue: The filter formats like Full HTML, Filtered HTML, PHP filter and Plain text in each content was not migrated
Solution: Since the filter formats are not migrated, a custom script was written to set the right format. Initially the filter format will be set to null and an empty string will be shown. Even PHP filter will not be set for the content and is not best practice to use it.
3. Admin structure page
Issue: Management menu has been migrated twice(one from d7 and another is in existing d8).
Solution: Delete the Drupal 7 menu links. Menu link with menu_name is from Drupal 8 whereas menu link with menu_id is from Drupal 7. Delete the menu link with menu id. This issue occurred only in our project and we were not able to replicate this issue in other migrations.
4. Date formats
Issue: Date formats are not migrated
Solution: Only the default short,medium and long formats are migrated. All other formats has to be reconfigured and recreated manually in Drupal 8.
5. “Output this field as a custom link” option in views not working
Issue: An option named “output this field as a custom link” found in the settings of the fields you add is not working in views
Solution: Apply the patch found in this link https://www.drupal.org/node/2488540(#100).
6. Jquery not loaded for anonymous user
Issue: For anonymous users some of the jquery was not loaded
Solution: This issue usually occurs in the Drupal 8 migration. We have followed the step found in this URL to add jquery for anonymous users. http://drupal.stackexchange.com/questions/109023/how-do-i-make-a-drupal-8-theme-require-jquery-for-anonymous-users
7. Mismatched entity and/or field definitions
Issue: Mismatched entity and/or field definitions error
Solution: The issue was solved by running custom script. The other solution to solve this issue is to run this command “drush entity-updates”. For more information see this link https://www.drupal.org/node/2601762
8. Outlook events
Issue: End date field not created and content not migrated
Solution: Deleted the existing date field and created a new date field with 'date and time' and checked 'end date'. The below patch was applied to create the end date field. A custom script was written to migrate the content.
Link for patch: https://www.drupal.org/files/issues/2161337-30.patch
9. Video field
Issue: Content and configuration for video field not migrated
Solution: The module used in Drupal 7 was not ported during our migration so we used an alternate module i.e Youtube Video module for this. We created a video field with this module and then applied a script for migrating the content from Drupal 7 to 8.
10. Link field
Issue: Field is migrated but the field configuration was mismatching and the contents were not migrated.
Solution: We reconfigured the field settings manually. A script was written to migrate the content.
Note: When saving the link through script, the external and internal link(link within the site)should be saved differently.
11. Entity reference
Issue: Field configurations was not migrated but both content and field was migrated.
Solution: In our project we were using multivalued entity reference field. The content type that has to be used as entity reference was not migrated and we configured the settings manually.
Issue: Views are not migrated
Solution: Currently there is no support to convert Drupal 7 views to Drupal 8, therefore views were created manually.
Issue: webform is not ported to Drupal 8 yet
Solution: Since there is no module for webform in Drupal 8. Contact Form from core came in handy and we did some custom code to support our functionality.
14. Boolean configuration
Issue: Field settings was not migrated
Solution: Although the content and the fields of boolean were migrated, the boolean field settings was not migrated. We manually configured the settings for this field.
15. Incorrect display of menu subtrees in menu block
Issue: Menu subtrees in menu blocks show all subitems regardless of the active menu item
Solution: A patch was applied to rectify the issue https://www.drupal.org/node/2631468#comment-10792980
Known issue list in Drupal: https://www.drupal.org/node/2167633
*Solutions are based on the availability of Drupal 8 modules during the time of project migration. Some of the issues might have been moved to core or fixed.