Add the Authors migration

web/modules/custom/geo_upgrade/migrations/upgrade_d7_node_story_author.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: upgrade_d7_node_story_author
+class: Drupal\migrate\Plugin\Migration
+field_plugin_method: alterFieldInstanceMigration
+cck_plugin_method: null
+migration_tags:
+  - 'Drupal 7'
+  - Content
+migration_group: migrate_drupal_7_geo
+label: 'Authors (Story authors)'
+source:
+  constants:
+    user_id: 1
+    author_status: 1
+  plugin: geod7_author
+process:
+  title: field_author_value
+  uid: constants/user_id
+  status: constants/author_status
+destination:
+  plugin: 'entity:node'
+  default_bundle: people
+migration_dependencies:
+  required: {  }
+  optional: {  }

web/modules/custom/geo_upgrade/src/Plugin/migrate/source/Author.php

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+<?php
+
+namespace Drupal\geo_upgrade\Plugin\migrate\source;
+
+use Drupal\migrate\Plugin\migrate\source\SqlBase;
+use Drupal\migrate\Row;
+
+/**
+ * Drupal 7 node source from database.
+ *
+ * @MigrateSource(
+ *   id = "geod7_author",
+ *   source_module = "geo_upgrade"
+ * )
+ */
+class Author extends SqlBase {
+
+
+  /**
+   * {@inheritdoc}
+   */
+  public function prepareRow(Row $row) {
+    $field_author = $row->getSourceProperty('field_author_value');
+    // Make sure to all the author names are trimmed.
+    $row->setSourceProperty('field_author_value', trim($field_author));
+
+    return parent::prepareRow($row);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function fields() {
+    $fields = [
+      'field_author_value' => $this->t('Author Name'),
+    ];
+    return $fields;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getIds() {
+    $ids['field_author_value']['type'] = 'string';
+    $ids['field_author_value']['alias'] = 'fdfa';
+
+    return $ids;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function query() {
+    $select = $this->select('field_data_field_author', 'fdfa')
+      ->fields('fdfa', [
+        'field_author_value',
+      ])
+    ->groupBy('field_author_value');
+
+    return $select;
+  }
+
+}