I have been trying to attach media entities to node entities in Drupal 8 with a custom migration but despite numerous attempts and countless hours reviewing forums i’m stumped – I’m desperately hoping someone can help explain where I might be going wrong.

Steps I have taken:

1. Created a custom migration to import files (Using Migrate Plus & Migrate Source CSV) – successful

2. Custom migration to import files into Drupal media entities (image bundle) – successful

Now that I have the media imported, I am trying to reference it so I can look to ditch the normal default field_image.

CSV format:

fid, uid, filename, filepath, uri, filemime, filesize, status, timestamp, uuid, alt  

As the files are now media elements I know I can’t reference them by file ID (FID), presumably it would be the media ID (MID) but I have no idea how to get this.

I tried to use the migrate_lookup to reference the existing migrations but during import i’m not getting any error messages which makes it hard to tell whether i’m targeting the right thing or not.

I have also tried to add a default value to test a single value but this also didn’t work.

id: news_nodes label: News Articles migration_group: custom  dependencies:   enforced:     module:       - migrate_custom  source:   plugin: news_nodes   node_type: article   target: db_migration  destination:   plugin: entity:node   default_bundle: article  process:   nid: nid   vid: vid   uid:     plugin: default_value     default_value: 1   langcode:     plugin: default_value     source: language     default_value: en   title: title   uid: node_uid   status: status   created: created   changed: changed   promote: promote   sticky: sticky   revision_uid: revision_uid   revision_log: log   revision_timestamp: timestamp   body/format:     plugin: static_map     bypass: true     source: body_format     map:       1: plain_text       2: restricted_html       3: full_html       4: full_html   body/value: body_value   body/summary: body_summary   field_tags: tags    field_image: image   field_image:      -       plugin: migration_lookup       migration: import_files       source: filename     -       plugin: skip_on_empty       method: process    field_media_image:       plugin: sub_process       source: field_media_image       process:          target_id:           -              plugin: migration_lookup             migration: import_media_files             source: fid             no_stub: true           -               plugin: skip_on_empty             method: process    # field_media_image/target_id:   #   -   #     plugin: migration_lookup   #     migration: import_files   #     source: image_fid   #   -   #     plugin: media_generate   #     destinationField: field_media_image   #     imageAltSource:    #       plugin: default_value   #       default_value: 'Featured image'   #     imageTitleSource:   #       plugin: default_value   #       default_value: 'Featured image'   #   -     #     plugin: skip_on_empty   #     method: process     field_news_companies: company_tags   field_news_companies:     plugin: sub_process     source: field_company_companies     process:       target_id: tid migration_dependencies:   required:     - custom_user     - import_files     - import_media_files     - upgrade_d7_taxonomy_term_company_companies     - upgrade_d7_taxonomy_term_tags 

The commented out section was trying this: https://drupal.stackexchange.com/a/249401/94547 however I get ‘Cannot load a NULL ID. in assert()’ error.

The node entity i’m trying to import to is the default article content type.

• Default image field – field_image
• Name of media field – field_media_image

I really would like to understand what i’m missing. I’m new to migrations so any advice on how to help would be appreciated!

EDIT

Having looked at a number of replies, I think we have narrowed down the issue to my source plugin plugin: news_nodes. which I am listing below.

The files/media have been imported using the CSV source but the nodes use custom PHP to query other custom fields which are required (taxonomy).

If I use the same source and plugin details as field_image in my field_media_image a media entity is referenced but not one that matches the file used in field_image. I’m guessing it’s passing the file id and the media entity is handing back a media item with the same numeric id.

Below is the custom plugin. For all I know the way I have set this up entirely wrong and needs to be re-made – any advice would be great.

Full code available on Github: https://github.com/lmonk72/migrate_custom

<?php  namespace Drupalmigrate_customPluginmigratesource;  use DrupalmigrateRow; use DrupalmigratePluginmigratesourceSqlBase;  /**  * @file  * Contains Drupalmigrate_customPluginmigratesourceNode.  */  /**  * Extract nodes from Drupal 7 database.  *  * @MigrateSource(  *   id = "news_nodes"  * )  */ class NewsNodes extends SqlBase {    /**    * {@inheritdoc}    */   public function query() {     // this queries the built-in metadata, but not the body, tags, or images.     $query = $this->select('node', 'n')       ->condition('n.type', 'article')       ->fields('n', array(         'nid',         'vid',         'type',         'language',         'title',         'uid',         'status',         'created',         'changed',         'promote',         'sticky',       ));     $query->orderBy('nid');     return $query;   }    /**    * {@inheritdoc}    */   public function fields() {     $fields = $this->baseFields();     $fields['body/format'] = $this->t('Format of body');     $fields['body/value'] = $this->t('Full text of body');     $fields['body/summary'] = $this->t('Summary of body');     $fields['field_image/target_id'] = $this->t('Image');     return $fields;   }    // /**   //  * {@inheritdoc}   //  */   public function prepareRow(Row $row) {     $nid = $row->getSourceProperty('nid');      // body (compound field with value, summary, and format)     $result = $this->getDatabase()->query('       SELECT         fld.body_value,         fld.body_summary,         fld.body_format       FROM         {field_data_body} fld       WHERE         fld.entity_id = :nid     ', array(':nid' => $nid));     foreach ($result as $record) {       $row->setSourceProperty('body_value', $record->body_value );       $row->setSourceProperty('body_summary', $record->body_summary );       $row->setSourceProperty('body_format', $record->body_format );     }      // taxonomy term IDs     // (here we use MySQL's GROUP_CONCAT() function to merge all values into one row.)     $result = $this->getDatabase()->query('       SELECT         GROUP_CONCAT(fld.field_tags_tid) as tids       FROM         {field_data_field_tags} fld       WHERE         fld.entity_id = :nid     ', array(':nid' => $nid));     foreach ($result as $record) {       if (!is_null($record->tids)) {         $row->setSourceProperty('tags', explode(',', $record->tids) );       }     }      // Company taxonomy term IDs     // (here we use MySQL's GROUP_CONCAT() function to merge all values into one row.)     $result = $this->getDatabase()->query('       SELECT         GROUP_CONCAT(fld.field_company_companies_tid) as tids       FROM         {field_data_field_company_companies} fld       WHERE         fld.entity_id = :nid     ', array(':nid' => $nid));     foreach ($result as $record) {       if (!is_null($record->tids)) {         $row->setSourceProperty('company_tags', explode(',', $record->tids) );       }     }      $result = $this->getDatabase()->query('       SELECT         fld.field_image_fid,         fld.field_image_alt,         fld.field_image_title,         fld.field_image_width,         fld.field_image_height       FROM         {field_data_field_image} fld       WHERE         fld.entity_id = :nid     ', array(':nid' => $nid));     // Create an associative array for each row in the result. The keys     // here match the last part of the column name in the field table.       $image = [];      foreach ($result as $record) {       $image[] = [         'target_id' => $record->field_image_fid,         'alt' => $record->field_image_alt,         'title' => $record->field_image_title,         'width' => $record->field_image_width,         'height' => $record->field_image_height,       ];     }     $row->setSourceProperty('image', $image);       return parent::prepareRow($row);   }    /**    * {@inheritdoc}    */   public function getIds() {     $ids['nid']['type'] = 'integer';     $ids['nid']['alias'] = 'n';     return $ids;   }    /**    * {@inheritdoc}    */   public function bundleMigrationRequired() {     return FALSE;   }    /**    * {@inheritdoc}    */   public function entityTypeId() {     return 'node';   }    /**    * Returns the user base fields to be migrated.    *    * @return array    *   Associative array having field name as key and description as value.    */   protected function baseFields() {     $fields = array(       'nid' => $this->t('Node ID'),       'vid' => $this->t('Version ID'),       'type' => $this->t('Type'),       'title' => $this->t('Title'),       'format' => $this->t('Format'),       'teaser' => $this->t('Teaser'),       'uid' => $this->t('Authored by (uid)'),       'created' => $this->t('Created timestamp'),       'changed' => $this->t('Modified timestamp'),       'status' => $this->t('Published'),       'promote' => $this->t('Promoted to front page'),       'sticky' => $this->t('Sticky at top of lists'),       'language' => $this->t('Language (fr, en, ...)'),     );     return $fields;   } } ?>