Cannot add foreign key constraint when value is NULL? - mysql

Question

I using CodeIgniter for develop my application, I have insert a constraint for this table:
Appointments
CREATE TABLE IF NOT EXISTS `appointments` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`GroupID` int(11) NOT NULL,
`book_datetime` datetime DEFAULT NULL,
`start_datetime` datetime DEFAULT NULL,
`end_datetime` datetime DEFAULT NULL,
`notes` text,
`hash` text,
`is_unavailable` tinyint(4) DEFAULT '0',
`guid_users_provider` char(36) DEFAULT NULL,
`guid_users_customer` char(36) DEFAULT NULL,
`guid_services` char(36) DEFAULT NULL,
`id_google_calendar` text,
`resources_guid` char(36) DEFAULT NULL,
`data` int(11) NOT NULL,
`lastUpdated` varchar(36),
PRIMARY KEY (`id`),
KEY `guid_users_customer` (`guid_users_customer`),
KEY `guid_services` (`guid_services`),
KEY `guid_users_provider` (`guid_users_provider`),
KEY `resources_guid` (`resources_guid`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
Resources
CREATE TABLE IF NOT EXISTS `resources` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`GUID` char(36) NOT NULL UNIQUE,
`descrizione` varchar(255) NOT NULL,
`sigla` varchar(255) NOT NULL,
`planning` varchar(255) NOT NULL,
`hex_color` varchar(255) NOT NULL,
`data` int(11) NOT NULL,
`lastUpdated` varchar(36),
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;
This is the constraint:
ALTER TABLE `appointments`
ADD CONSTRAINT `appointments_ibfk_5` FOREIGN KEY (`resources_guid`) REFERENCES `resources` (`GUID`) ON DELETE CASCADE ON UPDATE CASCADE;
The schema is builded correctly, but the problem is when I try to insert a record through my application, in particular the field resource_guid sometimes is NULL. Now, if I insert a record in PhpMyAdmin for test, in the appointments table and set the resource_guid as empty the record is added succesfully, but when I insert the record from my application on CodeIgniter I get this error:
Cannot add or update a child row: a foreign key constraint fails (scheduler.appointments, CONSTRAINT appointments_ibfk_5 FOREIGN KEY (resources_guid) REFERENCES resources (GUID) ON DELETE CASCADE ON UPDATE CASCADE)\",\"previous\":null,\
Now this is the content array of the query:
array(12) {
["guid_users_provider"]=>
string(36) "EE36D621-5E29-4674-81CB-B98622153E0C"
["start_datetime"]=>
string(19) "2015-12-30 23:19:00"
["end_datetime"]=>
string(19) "2015-12-31 00:45:00"
["notes"]=>
string(0) ""
["resources_guid"]=>
string(4) "null"
["is_unavailable"]=>
bool(false)
["guid_users_customer"]=>
string(36) "CDB8C010-7E51-4478-A341-F077E0460C88"
["guid_services"]=>
string(36) "31C40686-D72C-4361-B211-DCB2223552A9"
["book_datetime"]=>
string(19) "2015-12-31 01:12:39"
["hash"]=>
string(32) "5a9882faec12ab5bacb3445382176463"
["lastUpdated"]=>
string(27) "31-12-2015 10:12:39.5659760"
["GroupID"]=>
int(1)
}
How you can see the field resource_guid is NULL. Now the thing that I don't understand is (If I insert this in PhpMyAdmin as resource_guid set to NUll, so empty field, no error will be displayed, also from my application the error above appear).
This array is passed to the insert method of CodeIgniter like this:
if(!$this->db->insert('appointments', $appointment))
{
throw new Exception("Can't add record=> " . $this->db->_error_message());
}
How I can insert the resource also when is NULL? I mean, in my db table structure there is no renstriction for null value, infact in the appointments table is set with DEFAULT NULL. Someone could help me?

Answer 1

In your Appointments Table, you have given default value as NULL
Instead, give empty value as DEFAULT.
resources_guid` char(36) NOT NULL DEFAULT ''
To make an Existing Column as NOT NULL use MODIFY
ALTER TABLE Appointments MODIFY resources_guid char(36) NOT NULL DEFAULT ''

Answer 2

Look at your input resources_guid
["resources_guid"]=> string(4) "null"
It's a string with value "null", not a boolean NULL.
Pls check how you created that input. Make sure that is returning an actual NULL value. If you don't have control on that, you may need to change it manually by this way: (assuming the array as $appointment)
if($appointment["resources_guid"] == "null") {
$appointment["resources_guid"] = NULL;
}
Regarding the FOREIGN KEY, it should work as you have set it. There should be no problem for NULL values in the child field (unless the field is set as NOT NULL).