M:N relation with more fields - symfony

Question

So far the relations M:N I've built are simple intermediate tables where Doctrine does not need to create an entity for this table.
I have two entities Product and ingredient, they have a relationship M:N easily describe with Doctrine as follows. but the real problem is when i need store a amount field in the relation (I need to list the ingredients and also the amount).
How can solve this?
class Product {
//...
/**
* #var \Doctrine\Common\Collections\Collection
*
* #ORM\ManyToMany(targetEntity="MyBundle\Entity\Ingredient", inversedBy="product")
* #ORM\JoinTable(name="product_ingredient",
* joinColumns={
* #ORM\JoinColumn(name="product_id", referencedColumnName="id")
* },
* inverseJoinColumns={
* #ORM\JoinColumn(name="ingredient_id", referencedColumnName="id")
* }
* )
*/
private $ingredient;
//...
class Ingredient {
// ...
/**
* #var \Doctrine\Common\Collections\Collection
*
* #ORM\ManyToMany(targetEntity="MyBundle\Entity\Product", mappedBy="ingredient")
*/
private $product;
// ...

Answer 1

You can't do it without intermediate entity really, that's why doctrine docs says that ManyToMany relationships are rare.
It's also the easiest thing to do, just add RecipeItem entity which will store information about Ingredient and amount and link it with relationship of ManyToOne to Product
Edit
Since I was asked to provide an example:
class Product {
//...
/**
* #ORM\OneToMany(targetEntity="RecipeItem", mappedBy="product")
*/
private $ingredients;
//...
class RecipeItem {
// ...
/**
* #ManyToOne(targetEntity="Product", inversedBy="ingredients")
**/
private $product;
/**
* #ManyToOne(targetEntity="Ingridient")
**/
private $ingredient;
/**
* #Column(type="decimal")
**/
private $amount;
}
class Ingredient {
// Don't use bidirectional relationships unless you need to
// it impacts performance
}
Now having a product you can simply:
foreach($product->getIngridients() as $item){
echo "{$item->getAmount()} of {$item->getIngridient()->getName()}";
}