Datastore/src/Key.php
public function ancestorKey(Key $key)
    {
        if ($key->state() !== self::STATE_NAMED) {
            throw new InvalidArgumentException('Cannot use an incomplete key as an ancestor');
        }

        $path = $key->path();

        $this->path = array_merge($path, $this->path);

        return $this;
    }
public function ancestorKey(Key $key)
    {
        if ($key->state() !== self::STATE_NAMED) {
            throw new InvalidArgumentException('Cannot use an incomplete key as an ancestor');
        }

        $path = $key->path();

        $this->path = array_merge($path, $this->path);

        return $this;
    }
public function ancestorKey ( Key $ key ) { if ( $ key -> state ( ) !== self :: STATE_NAMED ) { throw new InvalidArgumentException ( 'Cannot use an incomplete key as an ancestor' ) ; } $ path = $ key -> path ( ) ; $ this -> path = array_merge ( $ path , $ this -> path ) ; return $ this ; }
Use another Key's path as the current Key's ancestor

Given key path will be prepended to any path elements on the current key.

Example:
```
$parent = $datastore->key('Person', 'Dad');
$key->ancestorKey($parent);
```

@param Key $key The ancestor Key.
@return Key
@throws InvalidArgumentException
Use another Key s path as the current Key s ancestor