Php Error with IF statements & validation - php

Question

I am trying to validate an input using a form, through the use of an if statement.
if (isset($_POST['weekly-rate']))
{
$weekly_rate = $_POST['weekly-rate'];
if(!isset($_POST['weekly-rate']))
{
$error_messages[]= 'Weekly rate was not set';
}
else
{
$weekly_rateOK = true;
}
}
else
{
$error_messages[] = 'Weekly rate was not set...';
}
When I run this it gives doesn't give me the output I want, which is Weekly rent was not set. Am I incorrect in thinking that
if(!isset($_POST['weekly-rate']))
{
$error_messages[]= 'Weekly rate was not set';`
Means, if an input is not set, run the error message, weekly rate was not set.
However all I receive is nothing

Answer 1

Your understanding of isset() is correct. However, the form always posts the field back to your backend code which triggers isset() to be true all the time. You may look at using empty() instead.
A simplified version would look like this
$weekly_rateOK = !empty($_POST['weekly-rate']);
if (!$weekly_rateOK) {
$error_messages[] = 'Weekly rate was not set...';
}
You may need to add an integer check if needed.

Answer 2

If you are using a text input/select with a name, then the input/select is always posted and is set, but with an empty string. If it is a checkbox or radio buttons, then they will be set only if the checkbox is checked or a radio button is selected.
I have written a sample validation function, inspired by Laravel. You can check it here, and extend it by adding additional cases:
function validate ($rule_bag, $input) {
$flag = true;
$error_bag = [];
foreach ($rule_bag as $item => $rules){
$rules = is_array($rules) ? $rules : array_filter(explode(',', $rules));
foreach($rules as $rule){
$rule = trim($rule);
switch(mb_strtolower(trim($rule))){
case 'required': {
// checking isset then empty to be compatible with php <= 5.4
if (!isset($input[$item]) || empty($input[$item]))
{
$flag = false;
!isset($error_bag[$item])?$error_bag[$item]=[]:null;
$error_bag[$item][] = $rule;
}
break;
}
default: {
if (isset($input[$item])){
try {
if (!preg_match($rule, $input[$item])){
$flag = false;
!isset($error_bag[$item])?$error_bag[$item]=[]:null;
!isset($error_bag[$item]['regex'])?$error_bag[$item]['regex']=[]:null;
$error_bag[$item]['regex'][] = $rule;
}
}
catch(Exception $e){
echo $e->getMessage();
}
}
}
}
}
}
return $flag ? $flag : $error_bag;
}