Only Generate Chart If PHP Variable Has Value

Question

I am using php & Charts.js to generate a chart of data based off an html <select> My issue is that even if nothing is selected from the html <select> a blank chart is displayed at the bottom of the page as opposed to displaying the echo statement in my else {} block.

How should I re-write this syntax so that a chart is ONLY created IF a selection is made from the html <select>

<body>
    <form method="POST">
    <p>Select Sales Name:
            <select name="Name">
                <option value="">Select A Name...</option>
                <option value="Joe">Joe</option>
                <option value="Jack">Jack</option>
                <option value="Jerry">Jerry</option>
                <option value="Jimmy">Jimmy</option></select></p>
        <input type="submit" name="submit" value="Show Me">
    </form>
</body>
<?php
if (isset($_POST['submit'])) {
    $whatsalesprsn = $_POST['Name'];
    if ($whatsalesprsn == "Joe") { $region = "East"; }
    if ($whatsalesprsn == "Jack") { $region = "West"; }
    if ($whatsalesprsn == "Jerry") { $region = "North"; }
    if ($whatsalesprsn == "Jimmy") { $region = "South"; }
    if (isset($region)) {
        $query = "Select * from salesdata where salesregion = '$region'";
        $db->setQuery($query);
        $rows = $db->loadColumn();
        $output = array();
        for ($i = 0; $i <= 3; $i++) {
        $column = $db->loadColumn($i);
        array_push($output, $column);
    }
    $data = json_encode($output[0]);
    } else { echo "PLease select a sales person to display data for."; }
}
?>

<html>
    <head>
        <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.6.0/Chart.min.js"></script>
    </head>
    <body>
        <div id="container" style="width: 75%;">
            <canvas id="canvas"></canvas>
        </div><script>
            //JavaScript to generate chart
        </script>
    </body>
</html>

@Mr.Developer - where do you propose I add this check into my current syntax? — BellHopByDayAmetuerCoderByNigh, Jul 19 '17 at 13:08
@Mr.Developer - where would the close bracket for the if statement be placed? I placed it after the select statement, and a blank chart is still presented. — BellHopByDayAmetuerCoderByNigh, Jul 19 '17 at 13:16
After this `$data = json_encode($output[0]);` Let me know if it is working — Ayaz Ali Shah, Jul 19 '17 at 13:18

score 0 · Answer 1 · answered Jul 19 '17 at 13:25

Somewhere you must be calling new Chart(...). If you do that without passing in valid data then Chart.js will create an empty chart (since that's what you told it to do).

If you've not got valid data (i.e. nothing's chosen in the the <select> element), don't instantiate Chart.js. Something like:

if (data.length) {
    new Chart(...);
}

score 0 · Accepted Answer · answered Jul 19 '17 at 13:28

You need to add if statement with empty() function. SO if if statement will check $whatsalesprsn variable if is empty or not by using empty() function

if(!empty($whatsalesprsn)){
 $whatsalesprsn = $_POST['Name'];
    if ($whatsalesprsn == "Joe") { $region = "East"; }
    if ($whatsalesprsn == "Jack") { $region = "West"; }
    if ($whatsalesprsn == "Jerry") { $region = "North"; }
    if ($whatsalesprsn == "Jimmy") { $region = "South"; }
    if (isset($region)) {
        $query = "Select * from salesdata where salesregion = '$region'";
        $db->setQuery($query);
        $rows = $db->loadColumn();
        $output = array();
        for ($i = 0; $i <= 3; $i++) {
        $column = $db->loadColumn($i);
        array_push($output, $column);
    }
    $data = json_encode($output[0]);
}

Only Generate Chart If PHP Variable Has Value

2 Answers2