Symfony2 simple many-to-many issue - symfony

Question

I have a simple question,
I have two tables in relation many to many, Post and Category,
in an intact form PostType a collection of form CategoryType, but here the problems begin ..
I followed the instructions on the cookbook collection form to persist the data, I just do not get the desired result ..
Here's the code:
class Post
{
/**
*
* #ORM\ManyToMany(targetEntity="Categories", inversedBy="posts", cascade={"persist", "remove"})
* #ORM\JoinTable(name="AnCat",
* joinColumns={
* #ORM\JoinColumn(name="post_id", referencedColumnName="id")
* },
* inverseJoinColumns={
* #ORM\JoinColumn(name="categories_id", referencedColumnName="id")
* }
* )
**/
protected $categories;
public function __construct()
{
$this->categories = new \Doctrine\Common\Collections\ArrayCollection();
}
public function addCategory($categories)
{
foreach ($categories as $category) {
$category->addPosts($this);
}
$this->categories[] = $categories;
}
class Categories
{
/**
*
* #ORM\ManyToMany(targetEntity="Post", mappedBy="categories")
*/
protected $posts;
public function __construct()
{
$this->posts = new ArrayCollection();
}
/**
*
* #param Post $post
* #return Categories
*/
public function addPosts(Post $posts)
{
// I tried it but I get the same result!
/*if (!$this->posts->contains($posts)) {
$this->posts->add($posts);
}*/
$posts->addCategory($this);
$this->posts[] = $posts;
}
class PostType extends AbstractType
{
->add('Categories', 'collection', array('type' => new CategoriesType(),
'allow_add' => true,
'allow_delete' => true,
'prototype' => true,
'prototype_name' => '__categ__',
'by_reference' => false
))
class CategoriesType extends AbstractType
{
->add('category', 'entity', array(
'attr' => array('class' => 'cat'),
'class' => 'MyBusinessBundle:Categories',
'property' => 'category',
'label' => 'Categories'
))
The problem is that inserts a new field Category, instead of creating a simple relationship Post-Category.
I don't understand where I'm wrong ..

Answer 1

In your postType, change collection type into entity Type
class PostType extends AbstractType
{
$builder->add('Categories', 'entity',
array( 'label' => 'Categories',
'required' => false,
'expanded' => true,
'class' => 'xxx\xxxBundle\Entity\Categories',
'property' => 'title',
'multiple' => true,
));
In your post creation form you will have checkboxes with categories. If you want a multi select field, change expanded by false