Your First Drupal 8 Migration

Drupal 8 Migration: A Deep Dive into Content Transfer

The Migrate module is a cornerstone of the Drupal ecosystem, so much so that core Drupal 8 integrated some of its functionality. This was crucial for replacing traditional upgrades with content and configuration migrations from Drupal 6 and 7 to Drupal 8. While core now includes the basic framework (in the migrate module) and Drupal 6/7 upgrade tools (in migrate_drupal), many essential features remain in contributed modules. Migrate Tools is particularly important, providing Drush commands and a user interface for managing migrations. Additionally, modules like Migrate Source CSV, Migrate Source XML, and Migrate Source JSON offer plugins for common data sources.

This article demonstrates Drupal 8 migration by importing content into node entities. For simplicity, we'll use database tables within the Drupal installation. The complete code is available in [this repository](link_to_repository_here - replace with actual link if available).

Key Concepts:

• Drupal 8 migrations consist of three parts: source, process, and destination. The source plugin fetches raw data, process plugins manipulate it, and destination plugins save it as Drupal entities.
• Migrate Tools is vital for running migrations via Drush (the recommended method). Commands like drush migrate-import --all and drush migrate-rollback --all control the process.

Migration Architecture:

A Drupal 8 migration uses the plugin system. The source plugin provides raw data, process plugins transform it, and destination plugins save it into Drupal entities. This pipeline is defined within a migration configuration entity (usually module config, imported on module enablement).

Example: Movie Migration

Our example involves two database tables: movies (id, name, description) and movies_genres (id, movie_id, name). The following MySQL script creates these tables and populates them with sample data:

<code class="language-sql">CREATE TABLE `movies` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  `description` text,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

CREATE TABLE `movies_genres` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `movie_id` int(11) DEFAULT NULL,
  `name` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

INSERT INTO `movies` (`id`, `name`, `description`) VALUES
(1, 'Big Lebowsky', 'My favorite movie, hands down.'),
(2, 'Pulp fiction', 'Or this is my favorite movie?');

INSERT INTO `movies_genres` (`id`, `movie_id`, `name`) VALUES
(1, 1, 'Comedy'),
(2, 1, 'Noir'),
(3, 2, 'Crime');</code>

The goal is to migrate movies into Article nodes and genres into Taxonomy terms (Tags vocabulary), maintaining the movie-genre association.

Genre Migration (migrate.migration.genres.yml):

<code class="language-yaml">id: genres
label: Genres
migration_group: demo
source:
  plugin: genres
  key: default
destination:
  plugin: entity:taxonomy_term
process:
  vid:
    plugin: default_value
    default_value: tags
  name: name</code>

The Genres.php source plugin (located in Plugin/migrate/source) defines the SQL query, fields, and IDs.

Movie Migration (migrate.migration.movies.yml):

<code class="language-sql">CREATE TABLE `movies` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  `description` text,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

CREATE TABLE `movies_genres` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `movie_id` int(11) DEFAULT NULL,
  `name` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;

INSERT INTO `movies` (`id`, `name`, `description`) VALUES
(1, 'Big Lebowsky', 'My favorite movie, hands down.'),
(2, 'Pulp fiction', 'Or this is my favorite movie?');

INSERT INTO `movies_genres` (`id`, `movie_id`, `name`) VALUES
(1, 1, 'Comedy'),
(2, 1, 'Noir'),
(3, 2, 'Crime');</code>

The Movies.php source plugin uses prepareRow() to add a 'genres' field containing genre IDs.

Activation and Execution:

1. Enable the custom module.
2. Install Migrate Tools.
3. Use Drush commands (migrate-status, migrate-import --all, migrate-rollback --all).

Conclusion:

This example illustrates Drupal 8's migration capabilities. Explore different source plugins, process plugins, and the potential for custom solutions to handle diverse migration needs.

Frequently Asked Questions (FAQs): (These are largely unchanged from the input, as they are factual and relevant.)

• What are the prerequisites for migrating to Drupal 8? (Answer remains the same)
• How do I prepare my Drupal 8 site for migration? (Answer remains the same)
• How do I perform the migration process? (Answer remains the same)
• What happens to my content during the migration process? (Answer remains the same)
• What should I do if the migration process fails? (Answer remains the same)
• Can I migrate my site’s configuration to Drupal 8? (Answer remains the same)
• How do I migrate my site’s theme to Drupal 8? (Answer remains the same)
• Can I roll back a migration? (Answer remains the same)
• How do I update my migrated content in Drupal 8? (Answer remains the same)
• Can I perform a partial migration? (Answer remains the same)

Remember to replace "link_to_repository_here" with the actual link if you have one.

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