php - 为什么这个 ajax 查询不返回成功结果？

Question

我无法理解为什么这个 ajax 查询失败，尽管它看起来很简单。我只是传递了一个新名称，并要求创建一个新记录，然后刷新一个包含新记录的选择列表。

这是将函数附加到新建、编辑、保存和取消按钮的 jQuery 代码：

var is_new = 0;

  $(document).ready(function()
  {
    // Attach event handlers to buttons
    $('#editbtn').on('click',pop_studyname);
    $('#newbtn').on('click',new_studyname);
    $('#savebtn').on('click',save_studyname);
    // disable the Save button until we have something to save
    $('#savebtn').attr('disabled',true);
    // disable the Cancel button until we have something to cancel
    $('#cancelbtn').attr('disabled',true);

  });

  function pop_studyname()
  {
    // pop the selected studyname into edit box.
    $('#edit_field').val($('#studylist :selected').text());
    // disable the New Study button
    $('#newbtn').attr('disabled',true);
    // enable the Cancel button
    $('#cancelbtn').attr('disabled',false);
    // and bind it to a function
    $('#cancelbtn').on('click',cancel_studyname);    
    // enable the Save button
    $('#savebtn').attr('disabled',false);
    // and bind it to a function
    $('#savebtn').on('click',save_studyname);
  }

  function new_studyname()
  {
    // clear edit box.
    $('#edit_field').val('');
    /**************************/
    /* set flag for New Study */
    is_new = 1;
    /**************************/

    // Enable the Cancel button
    $('#cancelbtn').attr('disabled',false);
    // and bind it to a function.
    $('#cancelbtn').on('click',cancel_studyname);
    // Disable the Edit button.
    $('#editbtn').attr('disabled',true);
    // Enable the Save button
    $('#savebtn').attr('disabled',false);
    // and bind it to a function.
    $('#savebtn').on('click',save_studyname);
    // put the cursor in the edit box
    $('#edit_field').focus();
  }

  function cancel_studyname()
  {
    // clear edit box.
    $('#edit_field').val('');
    // disable cancel button.
    $('#cancelbtn').attr('disabled',true);
    // disable Save button.
    $('#savebtn').attr('disabled',true);
    // Enable the Edit button.
    $('#editbtn').attr('disabled',false);
    // And the New Study button.
    $('#newbtn').attr('disabled',false);
    // Reset new study trigger variable. 
    is_new = 0;
  }

  function save_studyname()
  {
    // Are we saving a new or existing Study?
    if (is_new == 1) {
        $.ajax({
            type: 'POST',
            URL: "saveStudyName.php",
            data: {'type': 'new', 'studyname': $('#edit_field').val()},
        dataType: "json",
            success: function(resultmsg) {
              alert(resultmsg);
            },
            error: function() {
          console.log(resultmsg);
              alert('Huston, we have a problem...');
            }
        });
    // reset the trigger flag
    is_new = 0;

    }
    else {
      // Update an existing Study.
        // Get the record index and edited study name.
        var styndx = $('#studylist option:selected').val();
        var studyname = $('#edit_field').val();

    // Use ajax post call to update database.
        $.post("saveStudyName.php", {'type': 'update', 'studyname':studyname, 'styndx':styndx}, 
      function(resultmsg) {
      // refresh the picklist
      refresh_studynames();
      // clear the edit field
      $('#edit_field').val('');
      });      

    }
    // disable the Save button
    $('#savebtn').attr('disabled',true);
    // Enable the Edit button.
    $('#editbtn').attr('disabled',false);
    // Enable the New Study button.
    $('#newbtn').attr('disabled',false);
    // Finally, refresh the studyname picklist.
    refresh_studynames();
  }

这是被调用的 PHP 脚本：

 $type = $_POST['type'];
    $studyname = $_POST['studyname'];
    $styndx = $_POST['styndx'];

    //$a = json_decode($_POST[],true);
    $debug=0;
    if ($debug) { 
         echo "studyname = ".$studyname."<br>";
         echo "styndx = ".$styndx."<br>";
         echo "type = ".$type."<br>";
    }

    // query the database.
    $dbconnect = pg_pconnect("host=".$hostname." user=".$dbuser." dbname=".$dbname);    
    if (!$dbconnect)    {
        showerror(0,"Failed to connect to database",'saveStudyName',30,"username=".$dbuser.", dbname=".$dbname);
        exit;
    }

    if ($type == 'new') {
        $sql = "INSERT INTO ibg_studies (ibg_studyabrv) VALUES ('".$studyname."')";
    } else {
        $sql = "UPDATE ibg_studies SET studyabrv='".$studyname."' WHERE ibg_studies_index=".$styndx;        
    }


    $debug=0;
    if ($debug) { 
        echo "SQL = ".$sql;
    }

    $fetchresult = pg_exec($dbconnect, $sql);
    if ($fetchresult) {
        $msg = "Success!";
    } else {
        $msg = "Failure! SQL="+$sql;
    }

    echo json_encode($msg);

当我使用 Chrome 调试器单步执行 javascript 时，ajax 的成功或错误子句都不会触发，尽管我可以看到 jQuery 被调用......所以这对我来说是个谜！