Add new dynamic migration_lookup process plugin.

src/Plugin/migrate/process/MigrationLookupDynamic.php

@@ -0,0 +1,72 @@
+<?php
+
+namespace Drupal\up_migrate\Plugin\migrate\process;
+
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\Plugin\migrate\process\MigrationLookup;
+use Drupal\migrate\Row;
+
+/**
+ * Looks up the value of a property based on a previous migration.
+ *
+ * In contrast to the default migration_lookup, the migration can be dynamic
+ * based on a previous destination value.
+ *
+ * Examples:
+ *
+ * @code
+ * process:
+ * migration_name:
+ * plugin: static_map
+ * source: delta
+ * map:
+ * 0: users
+ * 1: accounts
+ * uid:
+ * plugin: migration_lookup
+ * migration: '@migration_name'
+ * source: author
+ * @endcode
+ *
+ * This switches migrations based on the source property "delta".
+ *
+ * @MigrateProcessPlugin(
+ * id = "up_migration_lookup_dynamic"
+ * )
+ */
+class MigrationLookupDynamic extends MigrationLookup {
+
+ /**
+ * {@inheritdoc}
+ */
+ public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+ $migration_ids = $this->configuration['migration_name'];
+ if (!is_array($migration_ids)) {
+ $migration_ids = [$migration_ids];
+ }
+ // Translate migration IDs if necessary.
+ foreach ($migration_ids as $key => $migration_id) {
+ $is_source = TRUE;
+ if ('@' === $migration_id[0]) {
+ $migration_id = preg_replace_callback('/^(@?)((?:@@)*)([^@]|$)/', function ($matches) use (&$is_source) {
+ // If there are an odd number of @ in the beginning, it's a
+ // destination.
+ $is_source = empty($matches[1]);
+ // Remove the possible escaping and do not lose the terminating
+ // non-@ either.
+ return str_replace('@@', '@', $matches[2]) . $matches[3];
+ }, $migration_id);
+ }
+ if ($is_source) {
+ $migration_ids[$key] = $row->getSourceProperty($migration_id);
+ }
+ else {
+ $migration_ids[$key] = $row->getDestinationProperty($migration_id);
+ }
+ }
+
+ $this->configuration['migration'] = $migration_ids;
+ return parent::transform($value, $migrate_executable, $row, $destination_property);
+ }
+
+}

src/Plugin/migrate/source/SqlBase.php

@@ -152,7 +152,7 @@ public function getConfig($name, $default = NULL) {
  */
  protected function initDatabases() {
  if (($databases = $this->state->get('up_migrate.databases')) === NULL) {
- throw new MigrateException('No source databases defined. Run `drush upm-database-add` to add at a database.');
+ throw new MigrateException('No source databases defined. Run `drush upm-database-add` to add a database.');
  }
  foreach ($databases as $key => $info) {
  // No need to check if the connection has been added before, since