How to add a default taxonomy term to all nodes in a migration?

Question

For a Drupal 7 to Drupal 8 migration, we're taking what was a Quotation content type and migrating it into an Article content type, joining a ton of nodes that are staying as Articles. To distinguish, I want to add a taxonomy term "Quotation" to the field_categories (which exists on Articles D7 and D8 but not on Quotation).

So i'm "simply" trying to add a value not from a source, but hard-coded. My source plugin is d7_node (namespace Drupal\node\Plugin\migrate\source\d7).

I'm flailing a bit; tried entity_generate but couldn't figure out how to tell it to use a constant and/or default value rather than looking for something from source.

Even this didn't work, when i tried to test the simplest thing i could think of when already knowing the term ID of an existing term:

  field_categories:
    plugin: iterator
    source: field_categories
    process:
      target_id:
        -
          plugin: default_value
          default_value: 10838

Can one use the default_value plugin or something like it for the 'source:'?

I'm about to stick my non-source value into what comes from the source with a prepare row hook, but it seems there ought to be an easier way.

Note that in this case there is nothing from field_categories in the source to worry about, but i'm also interested in the case of adding a new, hard-coded-into-the-migration term into a field that will have content, in my case field_tags.

Answer 1

Well, i don't like it, but this works:

<?php

use Drupal\migrate\Row;
use Drupal\migrate\Plugin\MigrateSourceInterface;
use Drupal\migrate\Plugin\MigrationInterface;

/**
 * Implements hook_migrate_MIGRATION_ID_prepare_row() for upgrade_d7_node_quote.
 */
function portside_upgrade_migrate_upgrade_d7_node_quote_prepare_row(Row $row, MigrateSourceInterface $source, MigrationInterface $migration) {
   $term_name = 'Portside Quotation';
   $term_array = \Drupal::database()->select('taxonomy_term_field_data', 't')
     ->fields('t', ['tid'])
     ->condition('vid', 'categories')
     ->condition('name', $term_name)
     ->execute()
     ->fetchCol();
   if (isset($term_array[0])) {
     $row->setSourceProperty('field_categories', [['tid' => $term_array[0]]]);
   }
}

I create the taxonomy term with default content, so it's there after site install and ready for the migration.

In the migration's YAML file (for upgrade_d7_node_quote), there's simply a plain mapping as if field_categories were a real thing:

  field_categories:
    plugin: iterator
    source: field_categories
    process:
      target_id: tid

And remember, there is no field_categories in the source. The migration doesn't mind at all and works fine with one inserted into the source in this prepare row hook.

Answer 2

I found the following worked for me...on the first migration I ran:

 field_type:
    -
      plugin: default_value
      default_value: 'Hall'
    -
      plugin: entity_generate
      entity_type: taxonomy_term
      value_key: name
      bundle: place_type

The second migration I ran, using exactly the same yaml to create the same content type, didn't work. I got a "Missing bundle for entity type taxonomy_term" error. Adding the bundle key as below fixed it:

 field_type:
    -
      plugin: default_value
      default_value: 'Library'
    -
      plugin: entity_generate
      entity_type: taxonomy_term
      value_key: name
      bundle_key: vid
      bundle: place_type