src/Forms/TreeDropdownField.php
protected function getCacheKey()
    {
        $target = $this->getSourceObject();
        if (!isset(self::$cacheKeyCache[$target])) {
            self::$cacheKeyCache[$target] = DataList::create($target)->max('LastEdited');
        }
        return self::$cacheKeyCache[$target];
    }
protected function getCacheKey()
    {
        $target = $this->getSourceObject();
        if (!isset(self::$cacheKeyCache[$target])) {
            self::$cacheKeyCache[$target] = DataList::create($target)->max('LastEdited');
        }
        return self::$cacheKeyCache[$target];
    }
protected function getCacheKey ( ) { $ target = $ this -> getSourceObject ( ) ; if ( ! isset ( self :: $ cacheKeyCache [ $ target ] ) ) { self :: $ cacheKeyCache [ $ target ] = DataList :: create ( $ target ) -> max ( 'LastEdited' ) ; } return self :: $ cacheKeyCache [ $ target ] ; }
Ensure cache is keyed by last modified datetime of the underlying list.
Caches the key for the respective underlying list types, since it doesn't need to query again.

@return DBDatetime
Ensure cache is keyed by last modified datetime of the underlying list . Caches the key for the respective underlying list types since it doesn t need to query again .