Migrate plugin migration_lookup : dynamic migration id

Question

"node_a_migration" is the migration ID of nodes of type "node_a"
"node_b_migration" is the migration ID of nodes of type "node_b"

I'd like to use either "node_a_migration" or "node_b_migration" as a migration_lookup depending on other field value.

The source (not a drupal site, entities of content A and content B can have the same id, because stored in different tables) :

[
  ['entity_type' => 'content_a', 'entity_id' => 123],
  ['entity_type' => 'content_b', 'entity_id' => 123],
]

The migration config :

process:
  pseudo_field_migration_id:
    plugin: static_map
    map:
      content_a: node_a_migration
      content_b: node_b_migration
    source: entity_type
  field_entity_reference:
    plugin: migration_lookup
    migration: '@pseudo_field_migration_id'
    source: entity_id

There is no error when running the migration, but the field_entity_reference is not populated.
It works if I manually replace '@pseudo_field_type_id' by node_a_migration

Any idea how to make it work ?

Thank you!

Answer 1

As @Hudri suggested, I've created my own process plugin (extending MigrationLookup plugin):

my_module/src/Plugin/migrate/process/CustomMigrationLookup.php

namespace Drupal\my_module\Plugin\migrate\process;

use Drupal\migrate\Plugin\migrate\process\MigrationLookup;
use Drupal\migrate\MigrateExecutableInterface;
use Drupal\migrate\Row;

/**
 * @MigrateProcessPlugin(
 *   id = "custom_migration_lookup"
 * )
 */
class CustomMigrationLookup extends MigrationLookup {
  
  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
    // We set the migration id based on the field configured in "migration_id_source"
    $this->configuration['migration'] = $row->getDestinationProperty($this->configuration['migration_id_source']);
    // We continue with the standard migration_lookup process
    return parent::transform($value, $migrate_executable, $row, $destination_property);
  }

}

The migration config :

process:
  pseudo_field_migration_id:
    plugin: static_map
    map:
      content_a: node_a_migration
      content_b: node_b_migration
    source: entity_type
  field_entity_reference:
    plugin: custom_migration_lookup
    migration_id_source: 'pseudo_field_migration_id'
    source: entity_id