如何为唯一电子邮件添加服务器端验证 - How to add server side validation for a unique email

How to add server side validation for a unique email

我有一个非常简单的表格，我用它来获取电子邮件地址以发送时事通讯。我正在尝试弄清楚如何添加一些服务器端验证以检查输入的电子邮件地址是否已在我的database中。然后，如果已经输入，则不允许提交表单，并引发用户可以看到的错误。

我将如何检查并显示错误？

<form action="" method="POST" id="newsletter-form">
    <input type="email" id="footer-grid1-newsletter-input" placeholder="Your Email Address" pattern=".{3,}" required>
    <input type="submit" id="footer-grid1-newsletter-submit" name="submit" value='&nbsp'>
</form>

 $("#newsletter-form").on("submit", function (event) {
        event.preventDefault();
        var newsletter_email = $("#footer-grid1-newsletter-input").val();
        var targeted_popup_class = jQuery(this).attr('data-popup-open');
        $.ajax({ 
            url: "newsletterSend.php", 
            type: "POST",
            data: {
                "newsletter_email": newsletter_email
            },
            success: function (data) {
            //  console.log(data); // data object will return the response when status code is 200
                if (data == "Error!") {
                    alert("Unable to insert email!");
                    alert(data);
                } else {
                    $("#newsletter-form")[0].reset();
                    $('.newsletter-popup').fadeIn(350).delay(2000).fadeOut();
                }
            },
            error: function (xhr, textStatus, errorThrown) {
                alert(textStatus + " | " + errorThrown);
                //console.log("error"); //otherwise error if status code is other than 200.
            }
        });
    });
$newsletter_email = $_POST['newsletter_email'];
try {
    $con = mysqli_connect("localhost", "", "", "");
    if (mysqli_connect_errno()) {
        printf("Connect failed: %s'n", mysqli_connect_error());
        exit();
    }
    $stmt = $con->prepare("INSERT INTO newsletter (email, subscribed) VALUES (?, NOW())");
        if ( false===$stmt ) {
            die('Newsletter email prepare() failed: ' . htmlspecialchars($con->error));
        }
    $stmt->bind_param('s', $newsletter_email);
        if ( false===$stmt ) {
            die('Newsletter email bind_param() failed: ' . htmlspecialchars($stmt->error));
        }
    $stmt->execute();
        if ( false===$stmt ) {
            die('Newsletter email execute() failed: ' . htmlspecialchars($stmt->error));
        }

下面的这个应该可以帮助你。

.JS：

$(document).ready(function(){ //newly added  
    $('#footer-grid1-newsletter-submit').click(function() {      
        var emailVal = $('#footer-grid1-newsletter-input').val(); // assuming this is a input text field       
        $.post('checkemail.php', {'email' : emailVal}, function(data) {
            if(data=='exist'){
                $('#alert').html("<p> You are already subscribed to our website</p>");
                return false;
            }
            else {
                $('#newsletter-form').submit();
            }
        });     
    });
});

.HTML：

<form action="" method="POST" id="newsletter-form">
    <input type="email" id="footer-grid1-newsletter-input" placeholder="Your Email Address" pattern=".{3,}" required>
    <input type="submit" id="footer-grid1-newsletter-submit" name="submit" value='&nbsp'>
</form>

.PHP：

$con = mysqli_connect("localhost", "", "", "");
if (mysqli_connect_errno()) {
    printf("Connect failed: %s'n", mysqli_connect_error());
    exit();
}

$sql = "SELECT email FROM newsletter WHERE email = '" .$_POST['email'] ."'";
$select = mysqli_query($con, $sql);
$row = mysqli_fetch_assoc($select);
if (mysqli_num_rows > 0) {
    echo "exist";
}
else {
    $stmt = $con->prepare("INSERT INTO newsletter (email, subscribed) VALUES (?, NOW())");  
}