Migrate multi-value paragraph field

Question

I'm doing a D7 to D8 custom migration. In Drupal 7, I have a multi-value formatted text field that I am trying to map to a Drupal 8 multi-value Paragraph entity reference field.

I've separated this into two migrations. One for the paragraphs, and one for the nodes themselves. I've got the multi-value field to paragraph migration working (although I think there might be an issue with the way that I have done the IDs). I have the node migration working as well, with the exception that none of the references to the already migrated paragraph entities are being migrated.

I realize that right now, this seems unnecessary, but it's part of a feature upgrade.

Below is the code from my migration classes/plugins.

This is from migrate_plus.migration.presentation_node.yml. Field_slide is the paragraph reference field.

'field_slide/target_id':
  plugin: migration
  migration: presentation_slide
  source: entity_id

This is the getIds function from PresentationSlide.php. This is the plugin for the paragraph migration.

public function getIds() {
  return [
    'entity_id' => [
      'type' => 'integer',
      'alias' => 'lt',
    ],
  ];
}

This is also from PresentationSlide.php. Here I am combining the entity_id and delta to form a unique id. I realize that this is a terrible way to do this, but I couldn't figure out anything better. Any tips on this are welcome.

public function prepareRow(Row $row) {
  $nid = $row->getSourceProperty('entity_id');
  $delta = $row->getSourceProperty('delta');
  $slide_id = (string) $nid . (string) $delta;
  $slide_id = (int) $slide_id;
  $row->setSourceProperty('entity_id', $slide_id);

  return parent::prepareRow($row);
}

And this is from PresentationNode.php. Here I am fetching all of the referenced fields, and passing that as an array to the migration class.

public function prepareRow(Row $row) {
  $nid = $row->getSourceProperty('nid');
  $query = $this->select('field_data_field_learning_text', 'lt')
    ->condition('entity_id', $nid);
  $query->addExpression('CONCAT(entity_id, delta)', 'target_id');

  $slides = $query->execute()->fetchCol(); 

  if (!empty($slides)) {
    $row->setSourceProperty('entity_id', $slides);
  }

  return parent::prepareRow($row);
}

The main issue here is that I can't figure out how to properly use a multiple column key. It seems to me that all of my issues are due to my doing this improperly.

Thanks in advance. I realize this is a lot.

[Edit]

Thanks Berdir for the help. I've taken a stab at implementing your processing plugin. However, I'm having an issue where the migration seems to be skipping right over and ignoring the process plugin.

field_slide:
  plugin: paragraph_process_base
  source: field_body_value

Feel like there is something super simple that I'm missing here.

[Edit 2] And I had a typo... Thanks a ton!

Answer 1

This is not directly an answer, but it is also too long for a comment :)

When I migrated something that wasn't actually paragraphs into paragraphs, I just wrote a custom process plugin that created paragraphs on the fly, then I didn't have to bother about trying to figure out some kind of mapping/made up ID's. What you're doing definitely seems like a bad idea, as 1010 could either be delta 10 from node 10 or delta 0 from node 101.

Put two classes I used for that into a gist: https://gist.github.com/Berdir/8a650a29a670fe283589f8946354086c.

It is both a bit hacky and a fairly complicated as I needed to support importing multiple translations for separate nodes in 6.x to a single node with a single paragraph with translations in 8.x.

Also created a to-do for me to write a blog post about this. ;)

Answer 2

Related blog post: https://deninet.com/blog/2017/06/18/building-custom-migration-drupal-8-part-5-paragraphs

There is a very popular post on Stack Overflow that suggests you write a custom process plugin. While this method can work, it's no longer recommended for Entity Reference Revisions 1.2 or higher.

Drupal.org handbook page would be really useful now..