Updating database rows using ajax and php

Question

I'm pretty new to php and jQuery. I've searched the net hi and low for an answer to no avail. I'm attempting to "post" an edit form that submits to itself using ajax and php. I'm able to return the values back to my form from the ajax.php. I'm also able to see them once they've posted, but the UPDATE query doesn't seem to be working. I'm not using ajax for anything other than getting values from a select. Something is hairy somewhere and I can't quite figure out where. I'm not too sure about my code either, but what I have seems to work up to/around the update query. Any help is much appreciated.

Here's my html, ajax call is at the bottom:

<?php //require_once("_includes/session.php"); ?>
<?php require_once("_includes/connection.php"); ?>
<?php require_once("_includes/functions.php"); ?>
<?php //confirm_logged_in(); ?>
<?php include("_includes/header.php"); ?>
<?php
if(isset($_POST['submit'])) {
    //$id = $_POST['postid'];
    //$title = $_POST['title'];
    //$content = $_POST['content'];
    //printf($id);
    //printf($title);
    //printf($content);
    $errors = array();

    // Form Validation
    $required_fields = array('title', 'content');
    foreach($required_fields as $fieldname) {
        if (!isset($_POST[$fieldname]) || (empty($_POST[$fieldname]) && !is_numeric($_POST[$fieldname]))) {
            $errors[] = $fieldname;
        }
    }

    $fields_with_lengths = array('title' => 50);
    foreach($fields_with_lengths as $fieldname => $maxlength ) {
        if (strlen(trim(mysql_prep($_POST[$fieldname]))) > $maxlength) { $errors[] = $fieldname; }
    }

    if (empty($errors)) {
        // Perform Update
        $id = mysql_prep($_POST['postid']);
        $title = mysql_prep($_POST['title']); 
        $content = mysql_prep($_POST['content']);

        $query = "UPDATE posts SET
                    title = '{$title}',
                    content = '{$content}',
                WHERE id = {$id}";
        $result = mysqli_query($connection, $query);
        if (mysqli_affected_rows($connection) == 1) {
            // Success
            $message = "The post was successfully updated.";
        } else {
            // Failed
            $message = "The subject update failed.";
            $message .= "<br>" . mysqli_error($connection);
        }

    } else {
        // Errors occurred
        if (count($errors) == 1) {
            $message = "There was " . count($errors) . " error in the form.";
        } else {
            $message = "There were " . count($errors) . " errors in the form.";
        }
    }

} // End: if(isset($_POST['submit']))
?>

<section id="manageContent">
<a href="manage.php">&lt&lt Back</a>

<h2>Edit Blog Post</h2>

<form id="newPost" name="newpost" action="edit_post.php" method="post">

<label for="posttitle">Select post title to edit:</label>

<select id="titleName" name="titleName">
    <?php
    $post_set = get_all_posts();
    while ($post = mysqli_fetch_array($post_set)) {
        echo '<option value="' . htmlspecialchars($post['id']) . '">'
            . htmlspecialchars($post['title'])
            . "</option>";
    }
    ?>
</select>

<p><label for="id">id:</label> <input id="postid" name="postid" type="text"></p>

<p><label for="title">Title:</label> <input id="title" name="title" type="text" required> (max length: 50 characters)</p>

<p><b>IMPORTANT!! things to remember so content is displayed how you would like:</b></p>
<ul>
    <li>You can use &ltp&gt, &ltdiv&gt, &ltul&gt, &ltol&gt, &ltli&gt tags in your blog posts.</li>
    <li>Insert the <b>&ltjumpbreak&gt</b> tag where you would like content to stop displaying on the main blog page.</li>
    <li>Enclose all remaining content after the <b>&ltjumpbreak&gt</b> in a <b>&ltdiv class="hideAfterJumpBreak"&gt&lt/div&gt</b> tag pair. This will keep all content after the <b>&ltjumpbreak&gt</b> from displaying on the main blog page until the topic is displayed on the topic.php page.</li>
    <li>Double check that every opening tag has a closing tag.</li>
</ul>

<p><label for="content">Content:</label></p>

<p><textarea id="content" name="content"></textarea></p>

<!--<p><button type="submit" name="submit">Edit Post</button></p> -->
<input id="submit" type="submit" name="submit" value="Edit Post">

<a href="edit_post.php"><button name="cancel">Cancel</button></a>
<a href="delete_post.php"><button name="delete">Delete</button></a>
</form>

<script>
(function() {

$("select#titleName").prop("selectedIndex", -1);

// returns a single item from php
/*
$("select#title").on("change", function() {
    var post_id = this.value;
    console.log(this);
    $.ajax ({
        url: "_includes/ajax.php",
        type: "POST",
        data: {post_id : post_id},
        dataType: "text",
        success: function(response) {
            $( "input#title" ).val(response);
        },
        failure: function() {
            alert("fail");
        }
    }); 
});
*/

$("select#titleName").on("change", function() {
    var post_id = this.value;
    console.log(this);
    $.ajax ({
        url: "_includes/ajax.php",
        type: "POST",
        data: {post_id : post_id},
        dataType: "json",
        success: function(response) {
            $( "input#postid" ).val(response.post_id);
            $( "input#title" ).val(response.post_title);
            $( "textarea#content" ).val(response.post_content);
        },
        failure: function() {
            alert("fail");
        }
    }); 
});

})();
</script>
</section>

<?php include("_includes/footer.php"); ?>

And here is my ajax.php:

<?php require_once("connection.php"); ?>
<?php require_once("functions.php"); ?>
<?php include_once("form_functions.php"); ?>
<?php
//if(isset($_POST['title'])) {
    //$post_id = $_POST['post_id'];
    //$query = "SELECT title, content
    //       FROM posts 
    //       WHERE id = '$post_id'";
    //$result = mysqli_query($connection, $query);
    //$row = mysqli_fetch_array($result);
    //echo $row['title'], $row['content'];
//}
    $post_id = $_POST['post_id'];
    $query = "SELECT *
             FROM posts 
             WHERE id = '$post_id'";
    $result = mysqli_query($connection, $query);
    $row = mysqli_fetch_array($result);
    echo json_encode(
        array("post_id" => $row['id'], 
        "post_title" => $row['title'],
        "post_content" => $row['content'])
    )

    //echo $row['title'], $row['content'];
?>


<?php mysqli_close($connection); ?>

Answer 1

Figured it out, in my UPDATE posts SET I had a comma after my second row update. Thank you all for the suggested readings as well.