PHP MySQL maths update value in database [closed] - php

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So ive got a rating system in place on a website im making. Currently each itema has a plus and minus button on either side as well as a visible rating level in this case its 3.1 for one of the items.
Im trying to programme both the plus and minus buttons in such a way that when the user presses them then the rating either increases or decreases by one.
Currently ive only implemented the minus button, however, when I click it the rating value doesnt decrease. It stays at 3.1. The page works fine and when i click on the "minus" button i get the error Call to a member function execute() on a non-object on line 67 which is the $stmt->execute()
Here is the code i have so far:
<?php
$results = $mysqli->query("SELECT * FROM programmes ORDER BY ProgrammeName ASC");
if ($results) {
$i=0;
echo '<table><tr>';
echo '<br/>';
echo '<br/>';
while($obj = $results->fetch_object())
{
echo '<td>';
echo '<div class="tvProgs">';
echo '<form method="post" id = "programmes" action="">';
echo "<input type=\"hidden\" name=\"progID\" value=\"".htmlentities($obj->ProgrammeID)."\" />";
echo '<div class="progImage"><img src="images/'.$obj->Image.'"></div>';
echo '<div class="progTitle"><h3>'.$obj->ProgrammeName.'</h3>';
echo '<div class="progRating"><h5>'.$obj->Rating.'</h5></div>';
echo '<div id = "btnMin"><input type="button" id ="minus" value ="-"/></div>';
echo '<div id = "btnPl"><input type="button" id ="plus" value ="+"/></div> ';
echo '<br/>';
echo '</form>';
echo '</div>';
echo '</td>';
$i++;
if ($i == 5) {
echo '</tr><tr>';
}
}
echo '</tr></table>';
}
if(isset($_POST['minus'])){
$newRating = 1;
$ID = $_POST['progID'];
$upsql = "UPDATE programmes SET Rating = Rating - $newRating WHERE progID='$ID'";
$stmt = $mysqli->prepare($upsql);
$stmt->execute();
}
?>
Ive kept the ID field hidden as i dont want that to be displayed on the web page. I just want to update the rating of a particular ID.
any informatino will be appreciated

Answer 1

Change your query from:
$upsql = "UPDATE programmes SET Rating = Rating - $newRating WHERE progID='$ID'";
To this:
$upsql = "UPDATE programmes SET Rating = Rating - $newRating WHERE ProgrammeID='$ID'";
Hope it should work..

Answer 2

For using _POST['some_name'] field on your form should have attribute name with value some_name
<input type="button" name="some_name" value="Some value"/>
Currently you have id="minus" which is not passed to a server. At least you should have:
<input type="button" id ="minus" name="minus" value="-" />
^ we got name here
And second thought - as your plus/minus buttons have no type="submit" I suppose your form doesn't submit, unless you have some hidden javascript.
Try setting you plus/minus buttons like:
<input type="submit" name="minus" value ="-"/>
<input type="submit" name="plus" value ="+"/>

Answer 3

Alternatively, you could use HTML5 number type input for your rating. Depending on the broswer you will have a little spinner that will do this task. Note that not all the broswers render this the same.
echo '<div class="progRating">
<h5><input type="number" id="rating" name="rating" value="'.$obj->Rating.'"/></h5></div>';
Then you have to update only the rating with its new value.
More info here: http://www.html5tutorial.info/html5-number.php