drupal_8_migrating_multivalue_fields.md

Drupal 8: Migrating Multi-value fields

field_telephone:
  -
    plugin: get
    source:
      - telephone_1
      - telephone_2
    -
      plugin: multiple_values

Migrate plugin

get: https://api.drupal.org/api/drupal/core%21modules%21migrate%21src%21Plugin%21migrate%21process%21Get.php/class/Get

Migrate Plus plugin

multiple_values: https://cgit.drupalcode.org/migrate_plus/tree/src/Plugin/migrate/process/MultipleValues.php