PHP operations on MongoDB gridfs storage files

<? PHP  //  Initialize gridfs  $ Conn = New Mongo (); //  Connect to MongoDB  $ DB = $ Conn -> Photos; //  Select Database  $ Grid = $ DB -> Getgridfs (); // You can retrieve gridfs objects. // There are three ways to store files. // The first method is to store files directly.  $ ID = $ Grid -> Storefile ("./logo.png" );  //  Second, stores the binary stream of a file.  $ Data = Get_file_contents ("./logo.png" );  $ ID = $ Grid -> Storebytes ( $ Data , Array ("Parame" => 'Additional parameters will be stored along with the image ')); //  Third, save the files submitted directly in the form $ _ files  $ ID = $ Grid -> Storeupload ('upfile' );  //  Equivalent  $ ID = $ Grid -> Storefile ( $ _ Files  ['Upfile'] ['tmp _ name']);  //  -------------- Save the image above -- start reading the image below -------------- // After the image is saved successfully, $ id = MD5 string is returned.  $ Logo =$ Grid -> Findone ( Array ('_ Id' => $ ID )); //  Use _ id as the index to retrieve files  Header ('Content-type: image/PNG '); //  Output Image Header  Echo   $ Logo -> Getbytes (); //  Output Data Stream ?>