Migrating Content Translated with "Content Translation" from Drupal 7 to Drupal 8

Since the release of Drupal 8 with a standardized way of managing translations, many sites running Drupal 7 are making a switch to Drupal 8. In Drupal 7 there are two ways to translate content:

  1. Using the content_translation module. The D7 core way of translating content, where every translation is a separate node.
  2. Using the entity_translation module. Maintains one node with a unique nid, while translations take place at the field level.

In this article we will discuss how to migrate content translations created with the content_translation module from Drupal 7 to Drupal 8. You can find our tutorial about migrating translations that use Entity Translation here.

This article would not have been possible without the help of my colleague Dave. ¡Gracias Dave!

The problem

We have a Drupal 7 database containing article nodes, which might have translations in English, Spanish and French. Some of these nodes are language-neutral, i.e. non-translatable. Our target is to migrate the Drupal 7 nodes into a Drupal 8 website, preserving the translations.

Before we start

  • Since this is an advanced migration topic, it is assumed you already know the basics of migration. If are new to migrations in Drupal 8, I recommend that you read about migrating basic data to Drupal 8 first.
  • If you'd like to run the migrations in this example yourself, see the quick-start documentation in our drupal migration i18n example repository.
  • The source website used in this example is Drupal 7.54.
  • The destination website used in this example is Drupal 8.3.x. However, an alternative solution for earlier versions is included towards the end of the article.

The module

To write the migrations, we create a module - in our case, migrate_example_i18n. There's nothing special about the module declaration, except for the dependencies:

  • migrate_plus and migrate_tools provide various features for defining and executing migrations.
  • migrate_source_csv: Will be used for demonstrating migration of translated content from non-Drupal sources in an upcoming article.
  • migrate_drupal: This module provides tools for migrating data from older versions of Drupal. It comes with Drupal 8.x core. Since this migration uses a Drupal 7 site as a source for its data, we need the migrate_drupal module.

How do translations work?

    Before jumping into writing these migrations, it is important to mention that Drupal 7 and Drupal 8 translations work very differently. Here's the difference in a nutshell:

    • Drupal 7: When we translate a node, a new node is created with a different ID. This translated node has a property named tnid, which stores the ID of the original node, linking the two nodes together. For language-neutral or untranslated content, the tnid is set to 0.
    • Drupal 8: When we translate a node, no new node is created! The translation is saved in the fields of the original node, but with a different language code.

    So just like we do when migrating translated content from Drupal 6 to Drupal 8, we create two migrations:

    • The example_dog_base migration will migrate the original content of each node, untranslated.
    • The example_dog_i18n migration will migrate only translations and associate them with original content created by example_dog_base.

    We group the two migrations using the example_dog migration group to keep things clean and organized. Then we can execute both migrations with drush migrate-import --group=example_dog --update.

    Step 1: Base migration

    We start with example_dog_base to migrate all base data or non-translations. Described below are some noteworthy parameters:

    Source

    source:  plugin: d7_node  node_type: article  key: drupal_7_content  constants:    uid_root: 1    node_article: 'article'

    • plugin: Since we want to import data from a Drupal installation, we need to set the source plugin to d7_node. The d7_node source plugin is introduced by the migrate_drupal, module and it helps us read nodes from a Drupal 7 database without having to write queries manually. Since Drupal 8.3.x, this plugin supports translations created with the content_translation module. If you are using an older version of Drupal 8, then check the alternative solution provided towards the end of this article.
    • node_type: This tells the source plugin that we are interested in just one particular Drupal 7 node type, namely article.
    • key: Our Drupal 7 data doesn't come from our main Drupal 8 database - instead it comes from a secondary database connection. We choose a key to identify each such connection and we need to tell the source which such key to use. The keys themselves are defined in the $databases variable in our settings.php or settings.local.php. See the example settings.local.php file to see how it's done.
    • constants: We define some hard-coded values under this parameter.
    • translations: Notice there is no translations parameter here. The default value (false) tells the source plugin that we're only interested in migrating non-translations, i.e. content in the base language and language-neutral content.

    Destination

    destination:  plugin: 'entity:node'

    • plugin: Since we want to create node entities in Drupal 8, we specify this as entity:node. That's it.
    • translations: Again we do not define the translations parameter while migrating base data. Omitting the parameter tells the destination plugin that we are interested in creating fresh nodes for each record, not translations of existing nodes.

    Process

    type: constants/node_articlelangcode:  plugin: default_value  source: language  default_value: unduid: constants/uid_roottitle: titlebody: bodyfield_one_liner: field_one_linersticky: stickystatus: statuspromote: promote

    This is where we map the old node properties to the new node properties. Most of the properties have been assigned as is, without alteration, however, some noteworthy properties have been discussed below:

    • nid: There is no nid parameter here, because we don't care what nid each new node has in Drupal 8. Drupal can just assign a new nid to each node in the normal way.
    • type: We specify that we want to create article nodes.
    • langcode: The langcode parameter was formerly language in Drupal 7, so we rename it here. Also, if a Drupal 7 node is language-neutral, the language property will have no value. In that case,  we default to und.

    This takes care of the base data. If we run this migration with drush migrate-import example_hybrid_base --update, all Drupal 7 nodes which are in base language or are language-neutral will be migrated into Drupal 8.

    Step 2: Translation migration

    We are halfway through now! All that's missing is migrating translations of the nodes we migrated above. To do this, we create another migration with the ID example_dog_i18n:

    source:  plugin: d7_node  node_type: article  translations: true  # ...destination:  plugin: 'entity:node'  translations: trueprocess:  nid:    plugin: migration    source: tnid    migration: example_dog_base  langcode: language  # ...migration_dependencies:  required:    - example_dog_base

    • source:
      • translations: We set this to true to make the source plugin read only translations.
    • destination:
      • translations: We set this to true to make the destination plugin create translations for existing nodes instead of creating fresh new nodes.
    • process:
      • nid: In this case, we do care what the Drupal 8 nid is for each node. It has to match the nid for the untranslated version of this content, so that Drupal can add a translation to the correct node. This section uses the migration (migration_lookup) process plugin to figure out the right nid. It tells Drupal to check the previously-executed example_hybrid_base migration for a D6 node that has the same tnid as this D6 node. It will then then reuse the resulting nid here.
      • langcode: We define the language in which the translation should be created.
    • migration_dependencies: Since we cannot add translations to nodes that do not yet exist, we tell Drupal that this migration depends on the base migration example_dog_base. That way, the base migration will run before this migration.

    That's it! We can run our translation migration with drush migrate-import example_dog_i18n --update and the translations will be imported into Drupal 8. Alternatively, we can use the migration group we defined to run both these migrations at once - the base migration will automatically be executed first and then the i18n migration. Here's how the output should look:

    $ drush migrate-import --group=example_dog --updateProcessed 7 items (7 created, 0 updated, 0 failed, 0 ignored) - done with 'example_dog_base'Processed 7 items (7 created, 0 updated, 0 failed, 0 ignored) - done with 'example_dog_i18n'

    You can check if everything went alright by clicking the Translate option for any translated node in Drupal 8. If everything went correctly, you should see that the node exists in the original language and has one or more translations.

    Article migrated from Drupal 7 to Drupal 8

    Alternate Solution for Drupal 8.2.x and Older

    The example code for this article works out of the box with Drupal 8.3 or higher. However, it will not work with earlier versions of Drupal 8. For Drupal 8.2 or older, we need to use a custom source plugin (inspired by the d6_node plugin). All we have to do is use the D7NodeContnentTranslation source plugin included in the code for this example, like source: d7_node_content_translation. This custom source plugin adds support for the translations parameter, which in turn makes the migration of content translations work correctly.

    Next Steps

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