Mad Max

@sttc

Please edit the post and mvoe your code to a place like pastebin.com, then post a link to the code.

The steps you’ve listed are ok. Double check function name: name used in the add_filter call must match with the defined function name.
If it seems all ok, there should be some erro in the logic of your code. Just to start, try to invert the condition you are using to check for duplicates, to see if something happens or use firefox+firebug to debug.

Well, just for the sake of completeness, here is the same code but using Michael’s API to access form data in the db:

// Add custom validation for CF7 form fields
function is_coupon_already_requested($email){ // Check if a customer has already request a discount coupon
	define ('FORM_NAME', 'Coupon');
	define ('FIELD_NAME', 'coupon_email');
	if (empty($email)) return false;
	$findit=false;
	require_once(ABSPATH . 'wp-content/plugins/contact-form-7-to-database-extension/CFDBFormIterator.php');
	$exp = new CFDBFormIterator();
	$exp->export(FORM_NAME, array('show' => FIELD_NAME, 'search' => $email));
	while ($row = $exp->nextRow()) {
		$findit=true;
	}
	return $findit;
}
function duplicate_email_validation_filter($result,$tag){
	define ('FIELD_NAME', 'coupon_email');
	$type = $tag['type'];
	$name = $tag['name'];
	if($name == FIELD_NAME){ // Only apply to fields with the form field name of "coupon_email"
		$the_value = $_POST[$name];
		if( !empty($the_value) && is_coupon_already_requested($the_value)){ //An user with this email has already received a coupon)
			$result['valid'] = false;
			$result['reason'][$name] = 'Email address already used.';
		}
	}
	return $result;
}
add_filter('wpcf7_validate_email','duplicate_email_validation_filter', 10, 2); // Email field
add_filter('wpcf7_validate_email*', 'duplicate_email_validation_filter', 10, 2); // Req. Email field

N.B.: Please note that if you pass an empty string as search value to the API, it returns all unfiltered rows for that query.
This is the reason why I added a check to see if the email field is empty or not.

Don’t know if someone is interested in this isssue any more, but I’ve find a way to make data validation against db submissions.

Thanks to this post, I’ve created a custom email validation function to avoid customers of one of my sites, to request more than one discount coupon with the same email address.

PLEASE NOTE: there’s no way to apply this custom validation to a particular form (i.e form id) cause the form id is not a parameter we can check using those validation filters.
So, if you have more then one form and you want to apply the custom validation only to a particular form, the only way I know is to use a univocal field name, or programmaticaly create a new type of field to use in your form and for your custom validation.
Obviously, every form using that field-id or that field-name, will make use of the custom validation function.

So, here is my code:

// Add custom validation for CF7 form fields
function is_coupon_already_requested($email){ // Check if a customer has already request a discount coupon
	global $wpdb;
	define ('FORM_NAME', 'Coupon');
	define ('FIELD_NAME', 'coupon_email');
	$query="SELECT
			submit_time,
				if(field_name='".FIELD_NAME."', field_value, null ) AS '".FIELD_NAME."'
		FROM ss_cf7dbplugin_submits
		WHERE form_name = '".FORM_NAME."' AND field_value='".$email."'
		";
	$myrows = $wpdb->get_results( $query, ARRAY_A );
	if (is_array($myrows) && count($myrows)){
		return true; //email already exists in the db
	}else{
		return false; // first time with this email
	}
}
function duplicate_email_validation_filter($result,$tag){
	define ('FIELD_NAME', 'coupon_email');
	$type = $tag['type'];
	$name = $tag['name'];
	if($name == FIELD_NAME){ // Only apply to fields with the form field name of "coupon_email"
		$the_value = $_POST[$name];
		if(is_coupon_already_requested($the_value)){ //An user with this email has already received a coupon)
			$result['valid'] = false;
			$result['reason'][$name] = 'Email address already used.';
		}
	}
	return $result;
}
add_filter('wpcf7_validate_email','duplicate_email_validation_filter', 10, 2); // Email field
add_filter('wpcf7_validate_email*', 'duplicate_email_validation_filter', 10, 2); // Req. Email field

Hope it can be useful

Graet Zack!! Thanks a lot!

Found this problem too.
There’s already a ticket open in the Trac here with its solution.
Just patch the core file if you are in a hurry and can’t wait for the next WP release.

I’ve added a few lines of code to take care of youtu.be urls. Just add the code below in vipers-vide-quicktags.php on line #2871

// Short/Share url ( http://youtu.be/videoid[?whatever=xx] )
elseif ( FALSE !== stristr( $content, 'youtu.be' ) ) {
	$parsed_url=parse_url($content);
	$videoid=basename($parsed_url['path']);
	$embedpath = 'v/' . $videoid;
	$fallbacklink = 'http://www.youtube.com/watch?v=' . $videoid;
	$fallbackcontent = '<img src="http://img.youtube.com/vi/' . $videoid . '/0.jpg" alt="' . __('YouTube Preview Image', 'vipers-video-quicktags') . '" />';
}

It also ignores query string parameters like t=xx added by youtube when a user selects a start time in the video.

Hope the plugin author could add those patch to the source code.