Migrating from D6/D7 to D8

Install migration modules

The following modules will help perform migrations using Drush:

• migrate_plus
  • Provides extensions to the core migration framework. The code also provides good plugin examples to look at.
• migrate_tools
  • Provides drush commands for managing and running migrations
• migrate_upgrade
  • Provides drush support for upgrading from Drupal 7 or 6 to Drupal 8
  • This is optional and used to export your Drupal 7 config that can be imported into Drupal 8. If you are updating field names, changing/manipulating data between sites or only migrating data these config files will need heavy modifications/updates.
  • The most helpful feature of this module is creating your migration_group yml file.
• migrate_devel
  • Provides debug information about fields during migration imports
  • This is an incredibly helpful module for devs creating migrations
  • Tells devs what fields are being mapped from and where they are mapping to, as well as the field’s data structure. It’s also a great way to see programmatically if your field is mapping at all or if it is skipping the field all together.

Create custom migration module

First, you will need to create a custom module that will hold your custom migration configuration that will be used to map the fields from your D6/D7 site to your D8 site. There are a couple of options here. You can either export and modify your D6/D7 config using migrate_upgrade or you can write the config files from scratch. All config should be put in custom_migrate_module/config/install

Export your Drupal 7 Config

Run the following shell script to export your D6/D7 config:

drush migrate-upgrade --legacy-db-url=mysql://user:pass@12.34.56.78/d6db --legacy-root=http://myd7site.com --configure-only
drush config-export --destination=/path/to/custom_migrate_module/config/install

Remove all non-migration config files, as well as any migration config files you do not need to use. If you are only migrating data from D6/D7 content types into a new D8 content type, all you need are the group, nodes and file yml files. You can ignore the field, taxonomy and revisions config.

Remember to remove the uuid key and value from the yml files you are going to use.

Add your custom module to the list of enforced dependencies to remove the config on uninstall. (This will be necessary when testing your config.)

dependencies:
 enforced:
   module:
     - custom_migrate_module

Modify the exported Drupal 7 config

This is the most labor intensive part of the migration process. If you are mapping the content to new fields you will need to have a deep understanding of the migration plugin system. When simply importing the data from one field to another with the same structure, you can use field_used_in_drupal8: field_from_drupal7

Hopefully, all you will need to do is a single one-to-one mapping for your fields.

field_used_in_drupal8: field_from_drupal7

A few plugins to be aware of are:

• default_value
• static_map
• format_date
• extract
• iterator
• migration_lookup

When migrating files, the basic structure you will need to use is:

field_used_in_drupal8:
   plugin: iterator
   source: field_from_drupal7
   process:
     target_id:
       plugin: migration_lookup
       migration: upgrade_d7_file
       source: fid
     alt: alt
     title: title
     height: height
     width: width

Migrating taxonomies can be done using the static_map plugin:

  field_used_in_drupal8:
      plugin: static_map
      source: field_from_drupal7
      map:
        d7ID1: d8ID1
        d7ID2: d8ID2
        d7ID3: d8ID3
        d7ID4: d8ID4
      bypass: true

You can perform several actions using multiple plugins on a single field by using the following format:

field_article_summary:
 -
   plugin: extract
   source: body
   default: ''
   index:
     - 0
     - summary
 -
   plugin: callback
   callable: strip_tags

Migration resources

• Migrate API overview
• Migration plugins
• Basic migration structure and concepts
• Migrating files