Symfony relational mapping many to one - php

Question

In my application I have a cigar humidor entity that has 8 slots. I would like each slot to hold an instance of any given of the hundreds of cigars there are to pick from.I can add a cigar to the cigar slot once for one humidor but I can not swap to a different humidor and add the same cigar to the slot1. I was thinking that with being in different humidors that it would surely not be an issue but I am now getting the exception "An exception occurred while executing 'UPDATE humidor SET slot_1 = ? WHERE id = ?' with params [2, 8]:SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry '2' for key 'UNIQ_4AE64E7F3CF622F8'"' I'm not exactly an expert with doctrine and am not totally sure on how I should go about modeling this. Any advice would be fantastic.
Here is the humidor with the slots
/**
* Humidor
*
* #ORM\Table(name="humidor")
* #ORM\Entity(repositoryClass="AppBundle\Repository\HumidorRepository")
*/
class Humidor
{
/**
* #var int
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #var string
*
* #ORM\Column(name="name", type="string", length=255, nullable=true)
*/
private $name;
/**
* #ORM\ManyToOne(targetEntity="UserBundle\Entity\User", inversedBy="humidors")
* #ORM\JoinColumn(name="user_id", referencedColumnName="id")
*/
private $user;
/**
* #ORM\OneToOne(targetEntity="Cigar")
* #ORM\JoinColumn(name="slot_1", referencedColumnName="id")
*/
private $slot1;
/**
* #ORM\OneToOne(targetEntity="Cigar")
* #ORM\JoinColumn(name="slot_2", referencedColumnName="id")
*/
private $slot2;
/**
* #ORM\OneToOne(targetEntity="Cigar")
* #ORM\JoinColumn(name="slot_3", referencedColumnName="id")
*/
private $slot3;
/**
* #ORM\OneToOne(targetEntity="Cigar")
* #ORM\JoinColumn(name="slot_4", referencedColumnName="id")
*/
private $slot4;
/**
* #ORM\OneToOne(targetEntity="Cigar")
* #ORM\JoinColumn(name="slot_5", referencedColumnName="id")
*/
private $slot5;
/**
* #ORM\OneToOne(targetEntity="Cigar")
* #ORM\JoinColumn(name="slot_6", referencedColumnName="id")
*/
private $slot6;
/**
* #ORM\OneToOne(targetEntity="Cigar")
* #ORM\JoinColumn(name="slot_7", referencedColumnName="id")
*/
private $slot7;
/**
* #ORM\OneToOne(targetEntity="Cigar")
* #ORM\JoinColumn(name="slot_8", referencedColumnName="id")
*/
private $slot8;
and then my cigar entity
/**
* Cigar
*
* #ORM\Table(name="cigar")
* #ORM\Entity(repositoryClass="AppBundle\Repository\CigarRepository")
* #ORM\HasLifecycleCallbacks()
*/
class Cigar
{
/**
* #ORM\PrePersist()
*/
public function onPrePersist(){
$this->setName($this->getManufacturer()->getName() . " " . $this->getVariant());
}
/**
* #var int
*
* #ORM\Column(name="id", type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
private $id;
/**
* #var int
*
* #ORM\Column(name="gauge", type="integer")
*/
private $gauge;
/**
* #var string
*
* #ORM\Column(name="body", type="string", length=255)
*/
private $body;
/**
* #var string
*
* #ORM\Column(name="wrapper_country", type="string", length=255)
*/
private $wrapperCountry;
/**
* #var string
*
* #ORM\Column(name="variant", type="string", length=255)
*/
private $variant;
/**
* #var string
*
* #ORM\Column(name="description", type="text")
*/
private $description;
/**
* #var string
*
* #ORM\Column(name="filler_country", type="string", length=255)
*/
private $fillerCountry;
/**
* #ORM\ManyToOne(targetEntity="Manufacturer", inversedBy="cigars")
* #JoinColumn(name="manufacturer_id", referencedColumnName="id")
*/
private $manufacturer;
/**
* #ORM\ManyToOne(targetEntity="Wrapper", inversedBy="cigars")
* #JoinColumn(name="wrapper_id", referencedColumnName="id")
*/
private $wrapper;
/**
* #ORM\ManyToOne(targetEntity="Shape", inversedBy="cigars")
* #JoinColumn(name="shape_id", referencedColumnName="id")
*/
private $shape;
/**
* #ORM\Column(type="string")
*
*/
private $image;
/**
* #var string
* #ORM\Column(type="string")
*/
private $name;

Answer 1

As you have one-to-one mapping, doctrine creates unique index for those columns. Let's consider this example (I've left only single slot as it's enough for this example):
id slot_1
1 11
2 12
This means that you have 2 cigars with IDs 11 and 12 assigned to humidor 1 and 2 respectively. There is unique index on slot_1 column here - this guarantees that any single cigar does not belong to two different humidors.
If you try to switch them, following SQL statements are generated:
UPDATE humidors SET slot_1 = 12 WHERE id = 1;
UPDATE humidors SET slot_1 = 11 WHERE id = 2;
Unfortunately, first statement cannot be executed, as database does not allow cigar 12 to be in both humidor 1 and 2 at once.
Simplest solution would be to change one-to-one relations to many-to-one (in your $slotX fields) - this would remove unique constraints, otherwise it would work the same in your example as there is no reverse relation. Furthermore, as there are 8 slots and cigars cannot belong to several of these (if I correctly understand), rules are already not strictly controlled by the database itself.
Another way would be to switch those with temporary null values etc. but it's even harder with doctrine, as you would need two separate flush statements and, optionally, manually wrapping these in a transaction to avoid inconsistent state in the database.