--- /dev/null
+<?php
+
+namespace Drupal\Core\Field\Plugin\Field\FieldType;
+
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+use Drupal\Core\Field\FieldItemBase;
+
+/**
+ * Defines the 'map' entity field type.
+ *
+ * @FieldType(
+ * id = "map",
+ * label = @Translation("Map"),
+ * description = @Translation("An entity field for storing a serialized array of values."),
+ * no_ui = TRUE
+ * )
+ */
+class MapItem extends FieldItemBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
+ // The properties are dynamic and can not be defined statically.
+ return [];
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public static function schema(FieldStorageDefinitionInterface $field_definition) {
+ return [
+ 'columns' => [
+ 'value' => [
+ 'type' => 'blob',
+ 'size' => 'big',
+ 'serialize' => TRUE,
+ ],
+ ],
+ ];
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function toArray() {
+ // The default implementation of toArray() only returns known properties.
+ // For a map, return everything as the properties are not pre-defined.
+ return $this->getValue();
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function setValue($values, $notify = TRUE) {
+ $this->values = [];
+ if (!isset($values)) {
+ return;
+ }
+
+ if (!is_array($values)) {
+ if ($values instanceof MapItem) {
+ $values = $values->getValue();
+ }
+ else {
+ $values = unserialize($values);
+ }
+ }
+
+ $this->values = $values;
+
+ // Notify the parent of any changes.
+ if ($notify && isset($this->parent)) {
+ $this->parent->onChange($this->name);
+ }
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function __get($name) {
+ if (!isset($this->values[$name])) {
+ $this->values[$name] = [];
+ }
+
+ return $this->values[$name];
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function __set($name, $value) {
+ if (isset($value)) {
+ $this->values[$name] = $value;
+ }
+ else {
+ unset($this->values[$name]);
+ }
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public static function mainPropertyName() {
+ // A map item has no main property.
+ return NULL;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function isEmpty() {
+ return empty($this->values);
+ }
+
+}