Can $_POST differentiate between two elements with the same name? - php

Question

New to PHP and reading through Robin Nixon's PHP, MySQL, Javascript book. I am having trouble with an example of inserting and deleting data using a PHP script, specifically with how the author uses $_POST.
The example is a pretty simple add records/delete records of books with multiple inputs. Here's the code:
if (isset($_POST['delete']) && isset($_POST['isbn']))
{
$isbn = get_post('isbn');
$query = "DELETE FROM classics WHERE isbn='$isbn'";
if (!mysql_query($query, $db_server))
echo "DELETE failed: $query<br />" .
mysql_error() . "<br /><br />";
}
if (isset($_POST['author']) &&
isset($_POST['title']) &&
isset($_POST['category']) &&
isset($_POST['year']) &&
isset($_POST['isbn']))
{
$author = get_post('author');
$title = get_post('title');
$category = get_post('category');
$year = get_post('year');
$isbn = get_post('isbn');
$query = "INSERT INTO classics VALUES" .
"('$author', '$title', '$category', '$year', '$isbn')";
if (!mysql_query($query, $db_server))
echo "INSERT failed: $query<br />" .
mysql_error() . "<br /><br />";
}
echo <<<_END
<form action="sqltest.php" method="post"><pre>
Author <input type="text" name="author" />
Title <input type="text" name="title" />
Category <input type="text" name="category" />
Year <input type="text" name="year" />
ISBN <input type="text" name="isbn" />
<input type="submit" value="ADD RECORD" />
</pre></form>
_END;
$query = "SELECT * FROM classics";
$result = mysql_query($query);
if (!$result) die ("Database access failed: " . mysql_error());
$rows = mysql_num_rows($result);
for ($j = 0 ; $j < $rows ; ++$j)
{
$row = mysql_fetch_row($result);
echo <<<_END
<pre>
Author $row[0]
Title $row[1]
Category $row[2]
Year $row[3]
ISBN $row[4]
</pre>
<form action="sqltest.php" method="post">
<input type="hidden" name="delete" value="yes" />
<input type="hidden" name="isbn" value="$row[4]" />
<input type="submit" value="DELETE RECORD" /></form>
_END;
}
mysql_close($db_server);
function get_post($var)
{
return mysql_real_escape_string($_POST[$var]);
}
?>
When you refer to an element in $_POST with if (isset($_POST['delete']) && isset($_POST['isbn'])), where delete and isbn are used as names multiple times, how does $_POST know which element to reference to delete? I assume that since you can only delete one record at a time, the element in the array will automatically point to the one that's already set. However, how does the second condition of isset($_POST['isbn']) know which "isbn" element to check for? Does the && make the $_POST['isbn'] "inherit" the correct row?
Thanks for the help! And apologies for any possible misuse of the vocab. Still getting used to everything.

Answer 1

Your question is actually well thought out. And the example given in the book seems quite sloppy to me. I am assuming in later chapters he will delve into the use of arrays in $_POST values. But anyway, here is the key to the functionality of the whole script:
for ($j = 0 ; $j < $rows ; ++$j)
{
$row = mysql_fetch_row($result);
echo <<<_END
<pre>
Author $row[0]
Title $row[1]
Category $row[2]
Year $row[3]
ISBN $row[4]
</pre>
<form action="sqltest.php" method="post">
<input type="hidden" name="delete" value="yes" />
<input type="hidden" name="isbn" value="$row[4]" />
<input type="submit" value="DELETE RECORD" /></form>
_END;
}
See that <form action="sqltest.php" method="post">? And see that closing </form>? And note that they are being rendered each time the for ($j = 0 ; $j < $rows ; ++$j) loop happens? There is one individual form element for each line. That is messy code, but it works. When one clicks submit on each individual listing, the wrapping form responds & parses the variables nested inside it.
Like I said, sloppy code. But works. And it’s because if you have 30 ISBNs listed this program will spit out 30 individually wrapped <form> items. Uggh! Seriously if the book does not address arrays later on in a way that addresses this face-palm of a coding mess find a new book.

Answer 2

Since there are multiple forms, the input elements of only one form are submitted.
So basically, sqltest.php receives only one array of $_POST containing ['delete'] and ['isbn'] with the corresponding values only once.
You can check this out by using print_r($_POST) in sqltest.php.