Update Only Changed Values to Database - php

Question

I have a form that I am trying to use to track batches of beer. Because the process of brewing takes several weeks or even months, I cannot complete the form all at once. When I first create a record for a beer, most of my values are set as NULL. When I retrieve the record and attempt to update it, it also updates all my NULL values to zeros. How can I send only changed values to the database from my form so the rest will be left as NULL?
Below is a sample of my update code (please forgive any PDO transgressions - it is my first foray into using PDO).
<?php
//Connect to Database
try {
$DBH = new PDO('mysql:host=localhost; dbname=dbname', 'user', 'password');
}
catch (PDOException $e) {
echo $e->getMessage();
exit();
}
//Build Update SQL Query
$update = "UPDATE brewlog
SET
BrewDate = :BrewDate,
EndOfPrimary = :EndOfPrimary,
EndOfSecondary = :EndOfSecondary,
PackagingDate = :PackagingDate,
AnticipatedOG = :AnticipatedOG,
WHERE ID = :ID";
//Prepare Query, Bind Parameters, Excute Query
$STH = $DBH->prepare($update);
$STH->bindParam(':ID', $_POST['ID'],PDO::PARAM_INT);
$STH->bindParam(':BrewDate', $_POST['BrewDate'],PDO::PARAM_STR,10);
$STH->bindParam(':EndOfPrimary', $_POST['EndOfPrimary'],PDO::PARAM_STR,10);
$STH->bindParam(':EndOfSecondary', $_POST['EndOfSecondary'],PDO::PARAM_STR,10);
$STH->bindParam(':PackagingDate', $_POST['PackagingDate'],PDO::PARAM_STR,10);
$STH->bindParam(':AnticipatedOG', $_POST['AnticipatedOG'],PDO::PARAM_INT);
$STH->execute();
?>

Answer 1

You would want to validate your data before you bind it. Say something like
if(!empty($_POST['EndOfPrimary'])) {
$eop = $_POST['EndOfPrimary'];
} else {
$eop = NULL;
}
Then bind
$STH->bindParam(':EndOfPrimary', $eop,PDO::PARAM_STR,10);
Edit:
You would also use this validation to check more than if the field was left blank. It looks like you probably want a date to be entered, so perhaps your would check if the user actually entered a date, and if not then send them back to the form with some type of helpful message about where they made the mistake. This is the regexp I use to validate a date.
function pcre_date($subject) {
return preg_match('/^[0-9]{1,2}\/[0-9]{1,2}\/[0-9]{4}$/', $subject);
/*
* matches 01/01/1984, 1/1/1984, but NOT 1/1/84
* wants mm/dd/yyyy
*/
} // returns 0 for non valid, 1 for valid
Then I would use this for the validation
if(!empty($_POST['EndOfPrimary'])) {
if(pcre_date($_POST['EndOfPrimary'])) {
$eop = $_POST['EndOfPrimary'];
} else {
$form_errors[] = "Please format date as mm/dd/yyyy.";
}
} else {
$eop = NULL;
}

Answer 2

To accomplish this cleanly, use two steps:
In the form presented to the user, maintain a list of changed fields. For example, when a user modifies the data in an input field, use Javascript to copy the contents of that field into a hidden form to be submitted. Then when the user clicks "submit", send only the contents of the hidden form, not the contents of the original form with all fields.
In your PHP script, build your query based on the fields provided. Your query will now include only the fields that were modified. This way, when you perform your UPDATE statement, the unchanged fields will be untouched.

Answer 3

Sorry george, I guess you are way far complicated of what he is trying to do.
Actually, when you use _POST['somevar'], if the field is blank, you get and EMPTY string.
and the empty string is saved to the database so the field is not NULL anymore
The simplest way to ensure the fields stay NULL in the database if there is no value captured is:
$STH->bindParam(':EndOfPrimary', isset($_POST['EndOfPrimary'])?$_POST['EndOfPrimary']:null ,PDO::PARAM_STR,10);