Populate second select list based on first select

问题:

This question already has an answer here:

• “Notice: Undefined variable”, “Notice: Undefined index”, and “Notice: Undefined offset” using PHP 28 answers

I'm trying to do a nested select list which is not working The values of the second select list dont get populated. Here is my code. I populate the first select and based on its value getter.php is called dynamically to populate the second select box (which is not working)

<div class="col-sm-3">
    <label for="rg">Region</label>
</div>
<div class="col-sm-9">
    <select id="region" name="region">
        <option value="">Select Region</option>
        <option value="AR">Ashanti</option>
        <option value="BRONG+AHAFO">Brong Ahafo</option>
        <option value="CENTRAL">Central</option>
        <option value="EASTERN">Eastern</option>
        <option value="GREATER+ACCRA">Greater Accra</option>
        <option value="NORTHERN">Northern</option>
        <option value="UPPER+EAST">Upper East</option>
        <option value="UPPER+WEST">Upper West</option>
        <option value="VOLTA">Volta</option>
        <option value="WESTERN">Western</option>
    </select>
</div>

<div class="col-sm-3"><label for="tw">Town</label></div>
<div class="col-sm-9">
    <select id="town" name="town">
        <option value="">Select Town</option>

    </select>
</div>


<script type="text/javascript">
$(document).ready(function() {
    $("#region").change(function() {
        $("#town").load("getter.php?choice=" + $("#region").val());
    });
});
</script>

Here is getter.php

<?php
include "../areashoppers/includes/cs_functions.php";
$sql = "SELECT distinct town FROM oic_areas_full WHERE region = '".$choice."' ORDER BY town ASC";
$st = $sc_conn->query($sql);
while ($r = $st->fetch()) {
    echo "<option>" . $r['town'] . "</option>";
}
?>

This is what shows in the error log

[02-Aug-2016 18:39:50 UTC] PHP Notice: Undefined variable: choice in /home/areashoppers/public_html/nylb/getter.php on line 3

[02-Aug-2016 18:39:50 UTC] PHP Fatal error: Call to a member function fetch() on boolean in /home/areashoppers/public_html/nylb/getter.php on line 5

$sc_conn is my DSN defined in cs_functions

回答1:

you have to get the choice from the url by GET method.

<?php
include "../areashoppers/includes/cs_functions.php";
$choice = $_GET['choice'];
$sql = "SELECT distinct town FROM oic_areas_full WHERE region='$choice' ORDER BY town ASC";
$st = $sc_conn->query($sql);
while ($r = $st->fetch()) {
  echo "<option>" . $r['town'] . "</option>";
}
?>

回答2:

Undefined variable: choice is most likely causing the second error as well, since the query will fail if $choice is not defined.

$choice = $_GET['choice'];

at the beginning of the PHP script should clear up the error.

Including a variable in the query string like getter.php?choice=something does not automatically create a $choice variable, but it does store the value in $_GET['choice'].

If you want to safely use the $choice variable in your query, don't worry about escaping it, just use a prepared statement. Assuming $sc_conn is a working PDO connection, that would be like this:

$sql = "SELECT distinct town FROM oic_areas_full WHERE region=? ORDER BY town ASC";
$st = $sc_conn->prepare($sql);
$st->execute([$choice]);