Specific form with two enities with Symfony - forms

Question

I have a Category entity, this entity allow me to create a tree of my data :
I would like to create a DiscountGrid entity. A DiscountGrid is composed by a textfield name, and an array containing the discount percentage by category ($discount[idCategory] = $percentage).
In fact, I would like a form like this :
The output would be $discount[ 1 ] = 25, $discount[ 2 ] = 30,.....
I have no idea how handle this behavior with Symfony framework. Here is the declaration of my entities
class Category{
/**
* #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)
*/
private $name;
/**
* #var string
*
* #ORM\Column(name="slug", type="string", length=255, nullable=true)
*/
private $slug;
/**
* #var int
* #Gedmo\TreeLeft
* #ORM\Column(name="lft", type="integer")
*/
private $lft;
/**
* #var int
* #Gedmo\TreeLevel
* #ORM\Column(name="lvl", type="integer")
*/
private $lvl;
/**
* #var int
* #Gedmo\TreeRight
* #ORM\Column(name="rgt", type="integer")
*/
private $rgt;
/**
* #Gedmo\TreeRoot
* #ORM\ManyToOne(targetEntity="Category")
* #ORM\JoinColumn(name="root", referencedColumnName="id", onDelete="CASCADE")
*/
private $root;
/**
* #Gedmo\TreeParent
* #ORM\ManyToOne(targetEntity="Category", inversedBy="children")
* #ORM\JoinColumn(name="parent", referencedColumnName="id", onDelete="CASCADE")
*/
private $parent;
/**
* #ORM\OneToMany(targetEntity="Category", mappedBy="parent")
* #ORM\OrderBy({"lft" = "ASC"})
*/
private $children;
class DiscountGrid{
/**
* #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)
*/
private $name;
/**
* #var string
*
* #ORM\Column(name="slug", type="string", length=255)
*/
private $slug;
/**
* #var array
*
* #ORM\Column(name="grid", type="array")
*/
private $grid;

Answer 1

First of all, what you are trying to do will be a nightmare if you keep storing DiscountGrid::$grid as an array. Not only this will make your form creation extremely hard, but what will happen if someday you have to add a Category? Will you drag all the indexes to match the new Categories list? This was not your question, and I may be downvoted for suggesting that, but I definitely recommend you build your model a bit cleaner, since having a clean model is mandatory to use FormTypes properly.
What I would suggest is the following model:
DiscountGrid::$grid (rename it to $discounts) is a ManyToOne of a new entity called Discount.
Discount has an attribute $category which is a OneToMany towards Category and an attribute $reduction which is a float.
Once you have this, create a DiscountFormType with a single field reduction which is a PercentType.
Then, create another form DiscountGridFormType with a single field discounts as a CollectionType. This CollectionType should have the option entry_type set as DiscountFormType.
Finally, when you create your form in Controller, bind it a DiscountGrid entity with some Discounts in your discounts attribute. You should see a series of text boxes with percents at the end. That's the list of discounts where you can change values of the reductions.
After that, some form theming will help you display the category name next to the textbox. But I guess you already have some way to go before being at this point.