PHP json_encode not working with array of objects
===

I am developing php application in which i am querying database and the generated result I am sending back to html client.

Currently I am getting array of objects which I am encoding in JSON using php function json_encode.

But after encoding I am getting null array in my result.

The following structure is before encoding to JSON



   

     array(2) {
      [0]=>   
          object(ProductComment)#6 (2) {
        ["_productId":"ProductComment":private]=>
        string(1) "1"
        ["_commentArray":"ProductComment":private]=>
        array(2) {
          [0]=>
          array(3) {
            ["comment"]=>
            string(9) "comment 1"
            ["creationDate"]=>
            string(19) "2000-02-02 00:00:00"
            ["userName"]=>
            string(8) "Ashutosh"
          }
          [1]=>
          array(3) {
            ["comment"]=>
            string(13) "comment1 text"
            ["creationDate"]=>
            string(19) "2012-07-31 10:20:27"
            ["userName"]=>
            string(8) "Ashutosh"
          }
        }
      }
      [1]=>
      object(ProductComment)#5 (2) {
        ["_productId":"ProductComment":private]=>
        string(1) "2"
        ["_commentArray":"ProductComment":private]=>
        array(2) {
          [0]=>
          array(3) {
            ["comment"]=>
            string(22) "comment2 product2 text"
            ["creationDate"]=>
            string(19) "2012-07-31 10:48:06"
            ["userName"]=>
            string(8) "Ashutosh"
          }
          [1]=>
          array(3) {
            ["comment"]=>
            string(22) "comment2 product4 text"
            ["creationDate"]=>
            string(19) "2012-07-31 10:48:14"
            ["userName"]=>
            string(8) "Ashutosh"
          }
        }
      }
    }

And after encoding it showing null instead of JSON.
Do i need to serialize it?
Anything advice will be appreciable.
Thanking you.
