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[yaffs-website] / web / core / modules / migrate / src / Plugin / migrate / process / Flatten.php

diff --git a/web/core/modules/migrate/src/Plugin/migrate/process/Flatten.php b/web/core/modules/migrate/src/Plugin/migrate/process/Flatten.php
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+<?php
+
+namespace Drupal\migrate\Plugin\migrate\process;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Row;
+
+/**
+ * Flattens the source value.
+ *
+ * The flatten process plugin converts a nested array into a flat array. For
+ * example [[1, 2, [3, 4]], [5], 6] becomes [1, 2, 3, 4, 5, 6]. During some
+ * types of processing (e.g. user permission splitting), what was once a
+ * one-dimensional array gets transformed into a multidimensional array. This
+ * plugin will flatten them back down to one-dimensional arrays again.
+ *
+ * Example:
+ *
+ * @code
+ * process:
+ *   tags:
+ *      -
+ *        plugin: default_value
+ *        source: foo
+ *        default_value: [bar, [qux, quux]]
+ *      -
+ *        plugin: flatten
+ * @endcode
+ *
+ * In this example, the default_value process returns [bar, [qux, quux]] (given
+ * a NULL value of foo). At this point, Migrate would try to import two
+ * items: bar and [qux, quux]. The latter is not a valid one and won't be
+ * imported. We need to pass the values through the flatten processor to obtain
+ * a three items array [bar, qux, quux], suitable for import.
+ *
+ * @see \Drupal\migrate\Plugin\MigrateProcessInterface
+ *
+ * @MigrateProcessPlugin(
+ *   id = "flatten",
+ *   handle_multiples = TRUE
+ * )
+ */
+class Flatten extends ProcessPluginBase {
+
+  /**
+   * Flatten nested array values to single array values.
+   *
+   * For example, [[1, 2, [3, 4]]] becomes [1, 2, 3, 4].
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    return iterator_to_array(new \RecursiveIteratorIterator(new \RecursiveArrayIterator($value)), FALSE);
+  }
+
+}