optional multiple oneToMany relation in symfony2 - php

Question

I have entities in Doctrine Symfony2: User, Channel, Video and Comment; user can report one of them. I designed Report entity with these fields:
userId
status
reportTime
description
how can I reference to reported Entity ?? because all reported fields are similar for all entities I want to use just one table for Report and add these fields to Report Entity:
referenceEntityName(a string and may be one of these: User, Channel, Video, Comment)
Channel(ManytoOne relation to Channel entity)
Video(ManytoOne relation to Video entity)
Comment(ManytoOne relation to Comment entity)
User(ManytoOne relation to User entity)
Is this best practice or I should create separate tables for each kind of report ??
Edit:
based on #Alex answer, I improved Report class and add these methods:
setEntity($entity){
if ($obj instanceof Video){
$this->referenceEntityName = 'Video';
$this->setVideo();
}
elseif($obj instanceof Comment){
$this->referenceEntityName == 'Comment'
$this->setComment();
}
//...
}
getEntity(){
if($this->referenceEntityName == 'Video'){
$this->getVideo()
}// ifelse statements for other entities ...
}
I till have 4 relation that just one of them is used for each instance, isn't it a bit messy!?
and again is this best practice or I should do something else?
what if I want to use FormBuilder class, isn't there any problem??

Answer 1

In a simple solution, whereby for example you only had Users (and not Videos, Comments and Channels), the solution would be simple; each User can have many Reports, and each Report must belong to only one User. This is a one-to-many relationship - one User has many Reports. In Symfony 2 and Doctrine, this would be modelled as such:
// src/Acme/DemoBundle/Entity/User.php
// ...
use Doctrine\Common\Collections\ArrayCollection;
class User
{
// ...
/**
* #ORM\OneToMany(targetEntity="Report", mappedBy="user")
*/
protected $reports;
public function __construct()
{
$this->reports = new ArrayCollection();
}
// ...
}
and
// src/Acme/DemoBundle/Entity/Report.php
// ...
class Report
{
// ...
/**
* #ORM\ManyToOne(targetEntity="User", inversedBy="reports")
* #ORM\JoinColumn(name="user_id", referencedColumnName="id")
*/
protected $user;
// ...
}
In this instance, to create a Report and associate it with a User, we would:
// get the User the Report will belong to
$user = $em->getRepository('AcmeDemoBundle:User')->find(1);
// create the Report
$report = new Report();
// add the User to the Report
$report->setUser($user);
// then persist it, etc ...
Note, the setUser() method is available because the console command was run to generate them automatically. This is highly recommended as it created the necessary type hinting for you. For pre Symfony 2.5 installations, the command is:
php app/console doctrine:generate:entities Acme
>= 2.5 installations, the command is:
php bin/console doctrine:generate:entities Acme
Your requirements complicate this simple example somewhat, as Reports can also belong to Comments and Videos etc. For the sake of the example, let's call these things Entities. A bad approach would be to simply add 3 new properties to the Report, one for each of the new Entities, and then add 3 new setter methods for the Entities. This is bad for 2 reasons: a Report will only ever belong to one of the Entities, and therefore 3 of the properties and setter methods will never be used for each Report entity. Secondly, if you add a new Entity to your business model, or remove one, you need to edit your Report entity, and also the database schema.
A better method is to simply have one property and set method in your Report, that can be applied to all of your Entities. So instead of calling setUser, we could call a setEntity, and have it accept any of the 4. With this approach in mind, let's look back at the first example, and take note of the type hinting in the function signature that would have been produced for the setUser method:
public function setUser(Acme\DemoBundle\Entity\User $user)
See that it requires to be of type Acme\DemoBundle\Entity\User. How do we overcome this, and have it accept any of the 4 Entities? The solution is to have all Entities be derived from a parent class. Then make the function type hint at the base class:
public function setUser(Acme\DemoBundle\Entity\Base $entity)
The base class will contain all common elements, notably a 'name', and as array collection of Reports:
// src/Acme/DemoBundle/Entity/Base.php
// ...
use Doctrine\Common\Collections\ArrayCollection;
class Base
{
// ...
/**
* #ORM\Column(name="name", type="text")
*/
protected $name
/**
* #ORM\OneToMany(targetEntity="Report", mappedBy="baseEntity")
*/
protected $reports;
public function __construct()
{
$this->reports = new ArrayCollection();
}
// ...
}
and then for each child, for example a User and a Video:
// src/Acme/DemoBundle/Entity/User.php
// ...
use AcmeDemoBundle\Entity\Base;
class User extends Base
{
/**
* #ORM\Column(name="firstname", type="text")
*/
protected $firstName;
// ...
}
and the Video
// src/Acme/DemoBundle/Entity/Video.php
// ...
use AcmeDemoBundle\Entity\Base;
class Video extends Base
{
/**
* #ORM\Column(name="title", type="text")
*/
protected $title;
// ...
and change our Report Entity:
// src/Acme/DemoBundle/Entity/Report.php
// ...
class Report
{
// ...
/**
* #ORM\ManyToOne(targetEntity="Base", inversedBy="reports")
* #ORM\JoinColumn(name="base_id", referencedColumnName="id")
*/
protected $baseEntity;
// ...
}
Remember to run the doctrine command to generate the setBaseEntity method. When you do, notice that it will now accept any class derived of Base
Then, to put on a Report on a Video for example, we get the Video, create a Report, and add the Video to the Report:
$video = // get the video you want
$report = new Report();
$report->setBaseEntity($video);
To retrieve all Reports belonging to a Comment, we get the Comment, and get the Reports:
$video = // get the video you want
$reports = $video->getReports();
foreach($reports as $report){
$reportText = $report->getText(); // assuming the Report has a `text` field
}
Update:
The inheritance relationship between these Entities can be modelled in the database with Doctrine using Single Table Inheritance:
/**
* #ORM\Entity
* #ORM\Table(name="base_entities")
* #ORM\InheritanceType("SINGLE_TYPE")
* #ORM\Discriminator(name="entity_type", type="string")
* #ORM\DiscriminatorMap({"user" = "User", "comment" = "Comment", "video" = "Video", "channel" = "Channel"})
*/