PHP $ _SESSION获取PHP注意：未定义的索引

Question

我有以下PHP代码，它通过PDO从SQL获取数据：

  $dbh->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
    $tableName = 'categories';

    ob_start();
    session_start(); 


    //Get values from table
    $sqlprimaryCategory = $dbh->prepare("SELECT * FROM $tableName GROUP BY primary_category");
    $sqlprimaryCategory->execute();
    echo '<form id="form1" action="" method="post">';
    echo '<select name="primary_category" size = "4" onChange="document.getElementById(\'form1\').submit();"> ';
    while ($resultprimary = $sqlprimaryCategory->fetch()) {
        echo '<option value="';
        echo $resultprimary['primary_category'];
        echo '">';
        echo $resultprimary['primary_category'];
        echo '</option>'; 
    }
    echo '</select>'; 
    //echo '<input type="submit" name="primary_category_button" id="primary_category_button" value="Submit">';
    echo '</form>'; 


    if (isset($_POST['primary_category'])) {
        $_SESSION['primary_category'] = $_POST['primary_category'];
        //unset($_SESSION['secondary_category']);
        //unset($_SESSION['tertiary_category']);

    }

    //Get values from table
    $sqlSecondaryCategory = $dbh->prepare("SELECT * FROM $tableName WHERE primary_category = :primary_category GROUP BY secondary_category");
    $sqlSecondaryCategory->execute(array(':primary_category'=>$_SESSION['primary_category']));
    echo '<form id="form2" action="" method="post">';
    echo '<select name="secondary_category" size = "4" onChange="document.getElementById(\'form2\').submit();"> ';
    while ($resultSecondary = $sqlSecondaryCategory->fetch()) {
        echo '<option value="';
        echo $resultSecondary['secondary_category'];
        echo '">';
        echo $resultSecondary['secondary_category'];
        echo '</option>'; 
    }
    echo '</select>'; 
    //echo '<input type="submit" name="secondary_category_button" id="secondary_category_button" value="Submit">';
    echo '</form>'; 


    if (isset($_POST['secondary_category'])) {
        $_SESSION['secondary_category'] = $_POST['secondary_category'];
        //unset($_SESSION['tertiary_category']);

    }


    //Get values from table
    $sqlTertiaryCategory = $dbh->prepare("SELECT * FROM $tableName WHERE secondary_category = :secondary_category GROUP BY tertiary_category");
    $sqlTertiaryCategory->execute(array(':secondary_category'=>$_SESSION['secondary_category']));
    echo '<form id="form3" action="" method="post">';
    echo '<select name="tertiary_category" size = "4" onChange="document.getElementById(\'form3\').submit();"> ';
    while ($resultSecondary = $sqlTertiaryCategory->fetch()) {
        echo '<option value="';
        echo $resultSecondary['tertiary_category'];
        echo '">';
        echo $resultSecondary['tertiary_category'];
        echo '</option>'; 
    }
    echo '</select>'; 
    //echo '<input type="submit" name="tertiary_category_button" id="tertiary_category_button" value="Submit">';
    echo '</form>'; 


    if (isset($_POST['tertiary_category'])) {
        $_SESSION['tertiary_category'] = $_POST['tertiary_category'];
        unset($_SESSION['tertiary_category']);

    }





    if (isset($_POST['primary_category']) OR isset($_POST['secondary_category']) OR isset($_POST['tertiary_category'])) {
        echo $_SESSION['primary_category'];
        echo $_SESSION['secondary_category'];
        echo $_SESSION['tertiary_category'];
    }

以上是一个下拉菜单。 第二个html下拉列表根据第一个选择的选择显示内容，而thrid下拉列表根据第二个下拉列表的选择显示内容。 如何修复我的代码以删除错误？

Answer 1

如果未发布第二个类别，则它不在session ，因此您将无法访问它。

您可以修复它，检查是否在您的第三个请求语句中使用$_SESSION['secondary_category']之前

if (isset($_POST['secondary_category'])) {
    $_SESSION['secondary_category'] = $_POST['secondary_category'];
    unset($_SESSION['tertiary_category']);
}elseif (!isset($_SESSION['secondary_category'])){
    $_SESSION['secondary_category'] = null;
}

Answer 2

if (isset($_POST['tertiary_category'])) {
    $_SESSION['tertiary_category'] = $_POST['tertiary_category'];
    //unset($_SESSION['tertiary_category']); < why unset right after assigning? (COMMENT OUT)

}




//Change OR's to AND's because the echo's will only work if all of them are set.
if (isset($_POST['primary_category']) AND isset($_POST['secondary_category']) AND isset($_POST['tertiary_category'])) {
    echo $_SESSION['primary_category'];
    echo $_SESSION['secondary_category'];
    echo $_SESSION['tertiary_category'];
}
// If you want to print out the ones that exist, make separate if statements for each category to see if they exist, or give them a blank value instead of unsetting them.