mssql里是datetime类型,显示不出来

Question

 [预开票日] => DateTime Object ( [date] => 2019-03-17 00:00:00.000000 [timezone_type] => 3 [timezone] => PRC ) 

[预收款日] => DateTime Object ( [date] => 2019-04-01 00:00:00.000000 [timezone_type] => 3 [timezone] => PRC ) 

判断是日期格式 用
echo "{$key} -> ".date_format($val,"Y-m-d") ." <br />"; 
还是不行. 请问怎样转换格式 谢谢.