Product and Sizes symfony2 doctrine example - php

Question

I'm new to symfony2 and I'm building my first online store with it. I have products and I want to add product sizes, one product can have many sizes and one size can have many products. For example: two products cat have 'M' size.
class Product {
...
/**
* #ORM\ManyToMany(targetEntity="Size", inversedBy="products", cascade={"persist", "merge"})
* #ORM\JoinTable(name="sizes")
*/
private $sizes;
}
//in another file
class Size {
/**
* #ORM\ManyToMany(targetEntity="Product", mappedBy="sizes")
*/
protected $products;
}
ProductController.php
...
->add('sizes', CollectionType::class, [
'entry_type' => SizeType::class,
'label' => 'Sizes',
'allow_add' => true,
])
...
SizeType.php
public function buildForm(FormBuilderInterface $builder, array $options) {
$repo = $this->em->getRepository('AppBundle:Size');
$q = $repo->createQueryBuilder('c')
->getQuery();
$sizes = $q->getResult();
$builder->add('name', EntityType::class, array(
'class' => 'AppBundle:Size',
'choice_label' => 'name',
));
}
Right now I'm getting
Catchable Fatal Error: Object of class AppBundle\Entity\Size could not be converted to string I can fix if I implement __toString() but I don't know if this is the right thing to do, and if I do this, when editing the product, the dropdown doesn't select the right size.
My question is, is this the right way to implement product - sizes function to online store?

Answer 1

Try with this code:
$builder->add('name', EntityType::class, array(
'class' => 'AppBundle:Size',
'choice_label' => 'name',
'property' => 'needed_property_name' //just write the needed property name there
));

Answer 2

So I've figured out better way to do it, 'entity' type with multiple => true
->add('sizes', 'entity', [
'class' => Size::class,
'label' => 'Размери',
'choice_label' => 'name',
'multiple' => true,
'expanded' => false,
//'allow_add' => true,
])
This way multiple sizes can be selected, with bootstrap-multiselect I've made it good looking and perfectly works for me now.
I'd love to hear if there is a better way.

Answer 3

Product annotations looks wrong. The JoinTable is a lookup table for many-to-many relation:
The convention is to name it after linked tables: products_sizes in your case:
class Product {
...
/**
* #ORM\ManyToMany(targetEntity="Size", inversedBy="products", cascade={"persist", "merge"})
* #ORM\JoinTable(name="products_sizes")
*/
private $sizes;
}