add validation "is_in_db"

application/helpers/hlp_common_helper.php

@@ -515,3 +515,31 @@ function has_permissions_for_stg($studiengang_kz, $permissions = '')
 
 	return false;
 }
+
+/**
+ * check if an entry exists in the database
+ */
+function is_in_db($key, $model = '')
+{
+	if (!$model)
+		return false;
+
+	$field = strstr($model, ":");
+	if ($field) {
+		$model = strstr($model, ":", true);
+		$field = substr($field, 1);
+	}
+
+	$CI =& get_instance();
+	$CI->load->model($model, $model);
+
+	if ($field) {
+		$result = $CI->$model->loadWhere([
+			$field => $key
+		]);
+	} else {
+		$result = $CI->$model->load($key);
+	}
+
+	return (isSuccess($result) && hasData($result));
+}

application/language/english/form_validation_lang.php

@@ -41,3 +41,4 @@ if (!defined('BASEPATH')) exit('No direct script access allowed');
 $lang['form_validation_has_write_permissions']	= 'You have no rights to edit {field} field.';
 $lang['form_validation_is_valid_date']	= 'The date format is invalid or out of range.';
 $lang['form_validation_has_permissions_for_stg']	= 'You have no rights for stg {field}.';
+$lang['form_validation_is_in_db']	= '{field} does not exist.';