symfony2嵌入式表单集合和实体映射

我学习了symfony2教程中关于如何创建嵌入式表单集合的内容，但由于它只创建了一个连接表，因此无法实现。

根据doctrine2文件："为什么多对多关联不太常见？因为通常你想将附加属性与关联关联关联，在这种情况下，你会引入一个关联类。因此，直接的多对多的关联消失了，取而代之的是3个参与类之间的一对多/多对一关联。"

以下是我的代码片段：

src/AppBundle/Entity/Ingradient.php

/**
* Defines the properties of the Ingredient entity to represent the portal ingredients.
*
* @author furious_snail
*
* @ORM'Entity()
* @ORM'Table(name="ingredients")
* @UniqueEntity("name")
*/
class Ingredient
{
/**
 * @ORM'Id()
 * @ORM'Column(type="integer")
 * @ORM'GeneratedValue(strategy="AUTO")
 */
private $id;
/**
 * @ORM'ManyToOne(targetEntity="IngredientCategory")
 * @ORM'JoinColumn(name="category_id", referencedColumnName="id", nullable=true)
 */
private $category;
/**
 * @ORM'Column(type="string", unique=true)
 */
private $name;
/**
 * @ORM'OneToMany(targetEntity="IngredientNutrient", mappedBy="ingredient", cascade={"persist", "remove"})
 */
private $nutrientsPer100G;
public function __construct()
{
    $this->substitute = new ArrayCollection();
    $this->nutrientsPer100G = new ArrayCollection();
}
public function getId()
{
    return $this->id;
}
public function setName($name)
{
    $this->name = $name;
}
public function getName()
{
    return $this->name;
}
/**
 * @param mixed $nutrientsPer100G
 */
public function setNutrientsPer100G($nutrientsPer100G)
{
    $this->nutrientsPer100G = $nutrientsPer100G;
}
/**
 * @return array
 */
public function getNutrientsPer100G()
{
    return $this->nutrientsPer100G;
}
}

src/AppBundle/Entity/IngradientNutrient.php

/**
 * @ORM'Entity()
 * @ORM'Table(name="ingredient_nutrient")
 */
class IngredientNutrient
{
/**
 * @ORM'Id()
 * @ORM'Column(type="integer")
 * @ORM'GeneratedValue(strategy="AUTO")
 */
private $id;
/**
 * @var integer
 *
 * @ORM'ManyToOne(targetEntity="Ingredient", inversedBy="nutrientsPer100G")
 * @ORM'JoinColumn(name="ingredient_id", referencedColumnName="id", nullable=true)
 */
protected $ingredient;
/**
 * @var integer
 *
 * @ORM'ManyToOne(targetEntity="Nutrient")
 * @ORM'JoinColumn(name="nutrient_id", referencedColumnName="id", nullable=true)
 */
protected $nutrient;
/**
 * @ORM'Column(type="float")
 */
private $quantity;
/**
 * @ORM'ManyToOne(targetEntity="Unit")
 * @ORM'JoinColumn(name="unit_id", referencedColumnName="id", nullable=true)
 */
private $unit;
/**
 * @return mixed
 */
public function getId()
{
    return $this->id;
}
/**
 * @return mixed
 */
public function getIngredient()
{
    return $this->ingredient;
}
/**
 * @param mixed $ingredient
 */
public function setIngredient($ingredient)
{
    $this->ingredient = $ingredient;
}
/**
 * @return mixed
 */
public function getNutrient()
{
    return $this->nutrient;
}
/**
 * @param mixed $nutrient
 */
public function setNutrient($nutrient)
{
    $this->nutrient = $nutrient;
}
/**
 * @return mixed
 */
public function getQuantity()
{
    return $this->quantity;
}
/**
 * @param mixed $quantity
 */
public function setQuantity($quantity)
{
    $this->quantity = $quantity;
}
/**
 * @return mixed
 */
public function getUnit()
{
    return $this->unit;
}
/**
 * @param mixed $unit
 */
public function setUnit($unit)
{
    $this->unit = $unit;
}
}

src/AppBundle/Form/Type/IngradientNutrientType.php

class IngredientNutrientType extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('nutrient', 'entity', array(
            'class' => 'AppBundle'Entity'Nutrient',
            'choice_label' => 'name',
            'label' => 'Nutrient',
        ))
        ->add('quantity', null, array('label' => 'Cantitate'))
        ->add('unit', 'entity', array(
            'class' => 'AppBundle'Entity'Unit',
            'choice_label' => 'unit',
            'label' => 'Unitate de masura'
        ));
}
public function configureOptions(OptionsResolver $resolver)
{
    $resolver->setDefaults(array(
        'data_class' => 'AppBundle'Entity'IngredientNutrient',
    ));
}
public function getName()
{
    return 'app_ingredient_nutrient';
}
}

src/AppBundle/Form/Type/IngradientType.php

class IngredientType extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
    $builder
        ->add('name', null, array('label' => 'Name'))
        ->add('nutrients_per_100_g', 'collection', array(
            'type' => new IngredientNutrientType(),
            'allow_add' => true,
            'label' => 'Nutrient quantity per 100g',
            'options' => array('label' => false),
        ));
}
public function configureOptions(OptionsResolver $resolver)
{
    $resolver->setDefaults(array(
        'data_class' => 'AppBundle'Entity'Ingredient',
    ));
}
public function getName()
{
    return 'app_ingredient';
}
}

这是可行的，我确实得到了一个嵌入的表单集合，但问题是ingredient_nutient表中的ingredient_id为null。如何用正确的ID填写表格？

这些是我在页面上得到的字段：

名称：

营养成分：

数量：

单位：

这个想法是，如果我有IngredientNutrient表格和Ingredient表格，用户不应该两次指定成分名称。

谢谢。