使用Fetch提交数据时PHP的POST数组为空问题求助

使用XAMPP搭建本地站点，开发Quiz更新功能时遇到问题：前端FormData和请求Payload都显示数据完整，但PHP端var_dump($_POST)和var_dump($_REQUEST)结果为空。另外有个奇怪的现象，另一个文件同样$_POST为空却能更新数据库，数据库连接正常（能正常读取数据）。

相关代码 #

处理请求的JavaScript代码 #

function saveQuiz() {
    const quizID = "<?php echo $quizid; ?>";
    const quizName = document.getElementById("quiz_name").value;

    const formData = new URLSearchParams();
    formData.append('quizName', quizName);
    formData.append('quizID', quizID);

    const questionTexts = document.querySelectorAll('.question-text');

    // Loop through the question texts and append them to formData
    questionTexts.forEach((textarea, index) => {
        formData.append(`question_texts[${index}]`, textarea.value);
    });

    console.log('FormData:', formData);
    for (const pair of formData.entries()) {
        console.log(pair[0] + ': ' + pair[1]);
    }//prints everything correctly

    fetch('updateQuiz.php', {
        method: 'POST',
        headers: {
            'Content-Type': 'application/x-www-form-urlencoded',
        },
        body: formData
    })
    .then(response => {
        console.log('submitted', response);
    })
    .catch(error => {
        console.error('error: ', error);
    });

    window.location.href = "../quiz/quizzesOverviewFaculty.php";
}

处理逻辑的updateQuiz.php文件 #

<?php
var_dump($_REQUEST);
session_start();

$host = "localhost";
$dbname = "course_resource_library";
$dbusername = "root";
$dbpassword = "";

//Creating connection to database
$conn = mysqli_connect(
    hostname: $host,
    username: $dbusername,
    password: $dbpassword,
    database: $dbname
);

if ($conn) {
    $quizID = $_POST['quizID'];
    $quizName = $_POST['quizName'];
  

    // Update the database with the new names
    $query = "UPDATE quiz SET quiz_name='$quizName' WHERE quiz_ID='$quizID'";
    $result = mysqli_query($conn, $query);

    //Retrieve question IDs and texts sent from the client-side
    $questionIDs = $_POST['question_ids'];
    $questionTexts = $_POST['question_texts'];

    // Check if the arrays have the same length
    if (count($questionIDs) === count($questionTexts)) {
        // Loop through the question IDs and texts
        for ($i = 0; $i < count($questionIDs); $i++) {
            $questionID = $questionIDs[$i];
            $questionText = $questionTexts[$i];

            $updateQuery = "UPDATE questions SET question = '$questionText' WHERE question_ID = '$questionID'";
        }

        // Check if the update was successful
        if ($conn->query($updateQuery) === TRUE) {
            // Successful update
            echo "Question with ID: $questionID updated successfully<br>";
        } else {
            // Failed to update
            echo "Error updating question with ID: $questionID - " . $conn->error . "<br>";
        }
    }
  
    if ($result) {
        // Update successful
        echo "Name updated successfully";
        echo $quizID;
        echo "  ";
        echo $quizName;
    } 
    else {
        // Error in updating
        echo "Error updating name: " . mysqli_error($conn);
    }
} 
else {
    echo "error: " . mysqli_error($conn);
}

mysqli_close($conn);
?>

提供数据的HTML代码 #

<div class="container container-fluid">
    <!-- This creates the thing in the middle that holds the info -->
    <div class="card h-4">
        <div class="card-header text-dark" style = "background-color:#CEB888">
                <div>
                    <span style="font-size: x-large; margin-left: 20px;"><b>Quiz Name: </b></span>
                    <input type="text" id="quiz_name" name="quiz_name" required="Yes" style="font-size: large;" value="<?php echo $quiz_name; ?>"> 
                </div>
        </div>
        <div class="card-body">
            <div class="card-body">
                <div class="row">
                    <div class="card h-100 w-100">
                        <div class="card-body">
                            <!-- Loop through number of questions -->
                            <?php
                                // Assuming you have already retrieved questions and answers from the database
                                // Repeat the loop for however many questions are in the quiz
                                foreach ($data as $row) {
                                    $questionId = $row["question_ID"];
                                    $questionText = $row["question"];
                                    ?>

                                    <!-- Display questions using html -->
                                    <h5 class="card-title text-dark">Question <?php echo $questionId; ?></h5>
                                    <p class="card-text text-dark"></p>
                                    <br>
                                    <textarea class="form-control question-text" rows="5" name="questions[<?php echo $questionId; ?>]"><?php echo $questionText; ?></textarea>
                                    <br>
                                    <span style="font-size: large; color: grey;">Answers:</span>
                                    <br>
                                    <br>
                                    <div class="row"> 
                                        <!--<input type="hidden" name="question_ids[]" value="<?php //echo $row["question_ID"]; ?>">
                                        <input type="hidden" name="question_texts[]" value="<?php //echo $row["question"]; ?>">-->
                                        <!-- Use php to get the current answer questions -->
                                        <?php
                                            //repeat the loop for however many answers there are
                                            foreach ($data2 as $row2) {
                                                $answerId = $row2["question_ID"];
                                                $answerText = $row2["answer_option"];
                                                if($answerId === $questionId) {
                                                    ?>
                            
                                                    <!-- Use html to display radio buttons and answers -->
                                                    <span>&nbsp;&nbsp;&nbsp;</span>

                                                    <!-- This will make sure the correct answer is selected -->
                                                    <?php
                                                    // check to see if current answer is the correct answer
                                                    if($row2["correct_answer"] == "yes")
                                                    {
                                                        ?>
                                                        <input type="radio" id="answer_<?php echo $answerId; ?>" name="question_<?php echo $questionId; ?>" value="<?php echo $answerId; ?>" required checked>
                                                        <?php
                                                    }
                                                    else
                                                    {
                                                        ?>
                                                        <input type="radio" id="answer_<?php echo $answerId; ?>" name="question_<?php echo $questionId; ?>" value="<?php echo $answerId; ?>" required="required">
                                                        <?php
                                                    }
                                                    ?> 
                            
                                                    <span>&nbsp;</span>
                                                    <input type="text" id="quiz_name" name="quiz_name" required="Yes" value="<?php echo $answerText; ?>" >
                                
                                                    <!-- End loop that goes through the questions -->
                                                    <?php
                                                }
                                            }
                                        ?>
                                    </div>

                                    <!-- End the big php loop -->
                                    <?php
                                }
                            ?>
                        </div>
                    </div>
                </div>
                <br>
                <!-- Buttons at the bottom of the page -->
                <div class="row">
                    <div class="d-flex justify-content-start align-items-center">
                        <a class="nav-link text-light btn mr-2" href="#" style="background-color:#0C8CE9; height: 30pt;"><b>Create Next Question</b></a>
                        <a class="nav-link text-light btn mr-2" style="background-color:#0C8CE9; height: 30pt;" onclick="saveQuiz()"><b>Save and Post</b></a>
                    </div>
                    <div class="d-flex justify-content-end align-items-center">
                        <a class="nav-link text-light btn" href="quizzesOverviewFaculty.php" style="background-color:#F54545; height: 30pt;"><b>Cancel</b></a>
                    </div>
                </div>
                <!-- Buttons at bottom of page -->
            </div>
        </div>
    </div>
</div>

问题排查与修复方案 #

1. 页面跳转中断请求 #

JavaScript最后执行的window.location.href会立即终止当前fetch请求，导致PHP无法完整接收数据，这是$_POST为空的核心原因。

修复： 将跳转逻辑移至fetch的then回调内，确保请求完成后再跳转：

fetch('updateQuiz.php', {
    method: 'POST',
    headers: {
        'Content-Type': 'application/x-www-form-urlencoded',
    },
    body: formData
})
.then(response => {
    console.log('submitted', response);
    // 请求完成后再执行跳转
    window.location.href = "../quiz/quizzesOverviewFaculty.php";
})
.catch(error => {
    console.error('error: ', error);
});

2. PHP代码顺序错误 #

session_start();必须放在所有输出之前，当前代码先执行var_dump($_REQUEST)触发输出，会导致session初始化失败，同时可能影响全局变量读取。

修复： 将session_start();移至PHP代码最顶部：

<?php
session_start();
var_dump($_REQUEST);
// 后续代码...

3. 缺失question_ids数据 #

前端仅提交了question_texts，但PHP尝试读取$_POST['question_ids']，且HTML中对应的隐藏域被注释，需补充数据提交：

修复： 取消HTML中的注释，或在前端手动添加到FormData：

// 在前端saveQuiz函数中添加question_ids的提交
const questionIds = document.querySelectorAll('input[name="question_ids[]"]');
questionIds.forEach(input => {
    formData.append('question_ids[]', input.value);
});

4. SQL注入风险 #

当前代码直接将用户输入拼接进SQL语句，存在严重安全隐患，必须使用预处理语句：

// 示例：更新quiz名称的预处理写法
$stmt = $conn->prepare("UPDATE quiz SET quiz_name=? WHERE quiz_ID=?");
$stmt->bind_param("si", $quizName, $quizID);
$stmt->execute();
$stmt->close();

内容的提问来源于stack exchange，提问作者Amber