17.8 AJAX Database

AJAX Database Example

The following example will demonstrate how a web page can fetch information from a database with AJAX:

Example Explained - The showCustomer() Function

When a user selects a customer in the dropdown list above, a function called showCustomer() is executed. The function is triggered by the onchange event:

function showCustomer(str) {
  var xhttp;
  if (str == "") {
    document.getElementById("txtHint").innerHTML = "";
    return;
  }
  xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
    document.getElementById("txtHint").innerHTML = this.responseText;
    }
  };
  xhttp.open("GET", "getcustomer.php?q="+str, true);
  xhttp.send();
}

• The showCustomer() function does the following:
  • Check if a customer is selected
  • Create an XMLHttpRequest object
  • Create the function to be executed when the server response is ready
  • Send the request off to a file on the server
  • Notice that a parameter (q) is added to the URL (with the content of the dropdown list)

The AJAX Server Page

• The page on the server called by the JavaScript above is a PHP file called "getcustomer.php".
• The source code in "getcustomer.php" runs a query against a database, and returns the result in an HTML table:

<?php
$mysqli = new mysqli("servername", "username", "password", "dbname");
if($mysqli->connect_error) {
  exit('Could not connect');
}

$sql = "SELECT customerid, companyname, contactname, address, city, postalcode, country
FROM customers WHERE customerid = ?";

$stmt = $mysqli->prepare($sql);
$stmt->bind_param("s", $_GET['q']);
$stmt->execute();
$stmt->store_result();
$stmt->bind_result($cid, $cname, $name, $adr, $city, $pcode, $country);
$stmt->fetch();
$stmt->close();

echo "<table>";
echo "<tr>";
echo "<th>CustomerID</th>";
echo "<td>" . $cid . "</td>";
echo "</tr>";
echo "<tr>";
echo "<th>CompanyName</th>";
echo "<td>" . $cname . "</td>";
echo "</tr>";
echo "<tr>";
echo "<th>ContactName</th>";
echo "<td>" . $name . "</td>";
echo "</tr>";
echo "<tr>";
echo "<th>Address</th>";
echo "<td>" . $adr . "</td>";
echo "</tr>";
echo "<tr>";
echo "<th>City</th>";
echo "<td>" . $city . "</td>";
echo "</tr>";
echo "<tr>";
echo "<th>PostalCode</th>";
echo "<td>" . $pcode . "</td>";
echo "</tr>";
echo "<tr>";
echo "<th>Country</th>";
echo "<td>" . $country . "</td>";
echo "</tr>";
echo "</table>";
?>