“如何使用user_id上传每个会话的图像”[复制]

Question

This question already has an answer here:

• “How to upload images per session with user_id” [duplicate]
• Reference - What does this error mean in PHP? 34 answers

"I want to images with user_id using session so user can display each picture which are display by them"

"I tried to $_SESSION[user_id] but it says Undefined index: user_id in E:\xampp\htdocs\photo\upload.php on line 195 Cannot add or update a child row: a foreign key constraint fails (photo.user_images, CONSTRAINT FK_user FOREIGN KEY (user_id) REFERENCES user (id))"

<?php
session_start();
if(isset($_SESSION['username']))

{
?>
<?php
 if(isset($_POST['btn']))
 {

 require_once("connection.php");


 $r = rand(111,999);

    $imgUrl = "images/".$r."_".$_FILES['img']['name'];
 move_uploaded_file($_FILES['img']['tmp_name'],$imgUrl);

 $query = "insert into user_images(`imagename`,`category`,`user_id`,`image`) values('".$_POST['imgname']."','".$_POST['category']."','".$_SESSION['user_id']."','".$imgUrl."')";

$result =  mysqli_query($con,$query) or die(mysqli_error($con));
if($result)
{
    echo '<p class="text-success">New Pic Information inserted';
}
 }

 ?>

"Cannot add or update a child row: a foreign key constraint fails (photo.user_images, CONSTRAINT FK_user FOREIGN KEY (user_id) REFERENCES user (id))"

</div>