class MapItem

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, [
                    'allowed_classes' => FALSE,
                ]);
            }
        }
        $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);
    }

}