jQuery, AJAX and JSON

jQuery, AJAX and JSON

I have a Select box that has an option to select Price Plan. When the price plan is selected, i want it to populate the PaymentAmount input box with the cost of that price plan.

The code i have so far,

HTML:
  1. <form name='dataForm' method='post' action='client.add.proc.php'  id='DataForm'>
  2. <table width='500' border='0' cellpadding='0' cellspacing='0'>
  3. <tr>
  4. <td width='150'><label>Payment Date</label></td>
  5. <td width='350'>
  6. <input type='hidden' name='Stage_field' value='AddContract' />
  7. <input type='hidden' name='Back_field' value='no' />
  8. <input type='text' name='paymentdate_field' id='dtepaymentdate'></td>
  9. </tr><tr>
  10. <td><label>Contract Type</label></td>
  11. <td>";
  12. makeSelectBox('typeofcover_field', true, "SELECT * FROM tbltypeofcover ORDER BY sortOrder", 'typeOfCoverID', 'typeOfCover', $_SESSION["TypeOfCoverID"], 'typeOfCoverID');
  13. echo"
  14. </td>
  15. </tr><tr>
  16. <td><label>Payment Amount (&pound;)</label></td>
  17. <td><input type='text' name='paymentamount_field' id='paymentamount_field' value='{$_SESSION["PaymentAmount"]}'></td>
  18. </tr><tr>
  19. <td><label>Contract Start</label></td>
  20. <td><input type='text' name='contractstart_field' id='dtecontractstart' value='{$_SESSION["ContractStart"]}'></td>
  21. </tr><tr>
  22. <td><label>Contract End</label></td>
  23. <td><input type='text' name='contractend_field' id='dtecontractend' value='{$_SESSION["ContractEnd"]}'></td>
  24. </tr><tr>
  25. <td>&nbsp;</td>
  26. <td>
  27. <button type='submit' class='back_id' name='Back_field' value='yes'>Back</button>&nbsp;
  28. <button type='submit' onClick=\"validateData();\">Next</button>
  29. </td>
  30. </tr>
  31. </table>
  32. </form>

JQUERY:
$(document).ready(function(){
      $('#typeofcover_field').change(function() {
      sendValue($(this).val());
      })
});

  1. function sendValue(str){
  2. $.post("client.add.contract_json.php", { sendToValue: str },
  3. function(data){
  4. $('#display').html(data.returnFromValue);
  5. }, "json");
  6. }

PHP - client.add.contract_json.php: 
  1. require_once('_include/maininclude.php');

  2. $TypeOfCoverID = $_POST['typeofcover_field'];

  3. $SQL = "SELECT * FROM tbltypeofcover WHERE typeOfCoverID = '$TypeOfCoverID'";
  4. $Result = mysql_query($SQL, $link) or die('Error, query failed<br>'.$SQL);
  5. $Row = mysql_num_rows($Result);
  6. $TypeOfCover = $row['typeOfCover'];
  7. $Cost = $row['Cost'];
  8. $LandlordPackage = $row['landlordPackage'];

  9. $arr = array('input#paymentamount_field' => $Cost);
  10. echo json_encode( $arr );

if i browse client.add.contract_json.php i get displayed: {"input#paymentamount_field":null} 

I think i am close, but seem to be going around in circles...

Thanks,
D