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Drupal Migrate Basic Fields to Entity References

In November 2022, the Drupal community and the Drupal Security Team will end their support for Drupal 7. By that time, all Drupal websites will need to be on Drupal 8 to continue receiving updates and security fixes from the community. The jump from Drupal 7 to 8 is a tricky migration. It often requires complex transformations to move content stuck in old systems into Drupal’s new paradigm. If you are new to Drupal migrations, you can read the official Drupal Migrate API, follow Mauricio Dinarte’s 31 Days of Drupal Migrations starter series, or watch Redfin Solutions’ own Chris Wells give a crash course training session. This blog series covers more advanced topics such as niche migration tools, content restructuring, and various custom code solutions. To catch up, read the previous blog posts Custom Migration Cron Job, Migration Custom Source Plugin, and Connecting a Transact SQL Database to Drupal.

Migrating from Drupal 7 to Drupal 8 often requires restructuring your content, like transforming an unlimited text field into paragraphs or a list text field into a taxonomy reference. The tricky part is that the migration pipeline wants each source entity to go to one destination entity, but each paragraph or taxonomy term is a new entity and a single node can reference several of these.

So how do you break up data from one entity and migrate it into multiple entities?


Manual entry

If there’s a small set of old content or you’re already manually adding new content, then manual entry is a viable solution, but it shouldn’t be the default for large migrations. Going this route, you want to set up content editors for easy success. If possible, reduce the number of actions needed for a repeated task. With some clever string concatenation in your query results, you can create exact links to all the node edit pages that need updating. This is much easier than giving someone a node id or page title and asking them to fix that page. Just because it’s not an automatic migration, doesn’t mean we can’t automate aspects of it.


CSV Importer

The CSV Importer module is useful for simple data that already exists in a CSV file or can be quickly exported as a CSV file. For example, a spreadsheet with hundreds of country names could easily be imported as taxonomy terms with this tool. Or a list of emails and names could be imported as Users. Once you’ve migrated your data, you can reference them in other migrations using the static_map plugin or a custom process plugin to lookup the correct entity reference. Be careful not to abuse the static_map plugin with hundreds of mappings. In the country example, if the source data contains the name of the country that you want to reference in the destination, you could write a process plugin that gets the taxonomy id from the name. Remember that once entities are migrated you can use the full power of Drupal to find their id’s in later migrations.


Generate entities during migration

Use the entity_generate plugin or a custom plugin to create the entities during the migration process. This gives more control over how the data is transformed, but there’s no way to rollback or update the generated entities through the migration API. This shouldn’t be the default, but can be necessary for more complicated matters such as breaking down a dense wysiwyg field into separate paragraphs (see Benji Fisher’s custom process plugin).


Migrate entities separately with a custom source plugin

See our earlier blog post for a step-by-step guide on this. Drupal core provides lots of useful source plugins, but sometimes you need a custom query to migrate specific source data into entities. This approach gives you that flexibility within Drupal’s migration workflow. Unlike the previous option, you can still rollback and update entities and leverage all the other migration tools.


How you perform a data transformation like this is largely contextual, but these are powerful tools that can be used in many cases. Contact us with any questions regarding complex Drupal migrations, or if you are looking for a Drupal agency to help with your next website project.