Error

gistfile1.txt

$entityClass = $this->getEntityClass();//API\V1\Entity\Site
$entity = new $entityClass;
$hydrator = $this->getHydrator();//DoctrineModule\Stdlib\Hydrator\DoctrineObject
$hydrator->hydrate((array)$data, $entity);

//data
object(stdClass)#658 (2) {
  ["id"]=>
  string(7) "testing"
  ["userId"]=>
  string(8) "mshwalbe"
}

Entity of type API\\V1\\Entity\\Site is missing an assigned ID for field  'id'. The identifier generation strategy for this entity requires the ID field to be populated before EntityManager#persist() is called. If you want automatically generated identifiers instead you need to adjust the metadata mapping accordingly.

hydrated entity

API\V1\Entity\Site Object
(
    [id:protected] => 
    [hashtags:protected] => Doctrine\Common\Collections\ArrayCollection Object
        (
            [_elements:Doctrine\Common\Collections\ArrayCollection:private] => Array
                (
                )

        )

    [userId:protected] => 
    [backgroundColor:protected] => 
    [headerBackgroundColor:protected] => 
)

siteentity

<?php

namespace API\V1\Entity;

use Doctrine\ORM\Mapping AS ORM;
use Doctrine\Common\Collections\ArrayCollection;

/**
 * @package    Model
 * @version
 * @ORM\Entity
 * @ORM\Table(name="site")
 * @ORM\ChangeTrackingPolicy("DEFERRED_EXPLICIT")
 */
class Site
{
    /**
     * @var String
     * @ORM\Id @ORM\Column(name="id", type="string", length=128)
     * 
     */
    protected $id;

    /**
     * @var \Doctrine\Common\Collections\ArrayCollection
     * @ORM\OneToMany(targetEntity="API\V1\Entity\HashTag", mappedBy="idSite")
     **/
    protected $hashtags;

    /** @ORM\Column(name="user_id", type="string", length=255, nullable=false) */
    protected $userId;

    /** @ORM\Column(name="background_color", type="string", length=7, nullable=true) */
    protected $backgroundColor;

    /** @ORM\Column(name="header_background_color", type="string", length=7, nullable=true) */
    protected $headerBackgroundColor;

    public function __construct() {
        $this->hashtags = new ArrayCollection();
    }

    public function getId()
    {
        return $this->id;
    }

    public function setId($id)
    {
        $this->id = $id;
    }

    public function setHashtags($hashtags)
    {
        $this->hashtags = $hashtags;
    }

    public function getHashtags()
    {
        return $this->hashtags;
    }

    /**
     * @return string $userId
     */
    public function getUserId()
    {
        return $this->userId;
    }

    /**
     * @param  string      $userId
     * @return Site
     */
    public function setUserId($userId)
    {
        echo 'set user id';
        exit;
        $this->userId = $userId;

        return $this;
    }

    /**
     * @return string $backgroundColor
     */
    public function getBackgroundColor()
    {
        return $this->backgroundColor;
    }

    /**
     * @param  string      $backgroundColor
     * @return Site
     */
    public function setBackgroundColor($backgroundColor)
    {
        $this->backgroundColor = $backgroundColor;

        return $this;
    }

    /**
     * @return string $headerBackgroundColor
     */
    public function getHeaderBackgroundColor()
    {
        return $this->headerBackgroundColor;
    }

    /**
     * @param  string      $headerBackgroundColor
     * @return Site
     */
    public function setHeaderBackgroundColor($headerBackgroundColor)
    {
        $this->headerBackgroundColor = $headerBackgroundColor;

        return $this;
    }
}