Warning: spl_object_hash() expects parameter 1 to be object - symfony

Question

Warning: spl_object_hash() expects parameter 1 to be object, string given in
/var/www/sitetwo/vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php line 1367
I created MainBlogBundle with Category.php and Product.php using yml mapping annotation via php app/console commands. After using CRUD actions for add/edit/delete/show actions I tried to add a category and after submitting Add category form I get the
Warning: spl_object_hash() expects parameter 1 to be object, string given in
/var/www/sitetwo/vendor/doctrine/orm/lib/Doctrine/ORM/UnitOfWork.php line 1367
I posted my sample code on github and below is the script of database.
git#github.com:veerpartap/ProblemSymfony.git
/****************************************************************************/
-- phpMyAdmin SQL Dump
-- version 3.4.10.1deb1
-- http://www.phpmyadmin.net
--
-- Host: localhost
-- Generation Time: Oct 26, 2013 at 01:56 PM
-- Server version: 5.5.32
-- PHP Version: 5.5.3-1+debphp.org~precise+2
SET SQL_MODE="NO_AUTO_VALUE_ON_ZERO";
SET time_zone = "+00:00";
--
-- Database: `sitetwo`
--
-- --------------------------------------------------------
--
-- Table structure for table `category`
--
CREATE TABLE IF NOT EXISTS `category` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=1 ;
-- --------------------------------------------------------
--
-- Table structure for table `Company`
--
CREATE TABLE IF NOT EXISTS `Company` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`company_name` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`address` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`owner_name` varchar(150) COLLATE utf8_unicode_ci NOT NULL,
`status` tinyint(1) NOT NULL,
`created` datetime NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=3 ;
--
-- Dumping data for table `Company`
--
INSERT INTO `Company` (`id`, `company_name`, `address`, `owner_name`, `status`, `created`) VALUES
(1, 'My First Company', 'Street 5A Sector 85 Chandigarh 1665588', 'Mr. Prateek Kumar', 1, '2013-09-06 00:00:00'),
(2, 'My Second Private Company', 'Street 34N Sector 89, Chandigarh 165898', 'Mr. Saurabh Shuja', 1, '2013-09-07 00:00:00');
-- --------------------------------------------------------
--
-- Table structure for table `Post`
--
CREATE TABLE IF NOT EXISTS `Post` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`title` varchar(250) COLLATE utf8_unicode_ci NOT NULL,
`body` longtext COLLATE utf8_unicode_ci NOT NULL,
`published` datetime NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=1 ;
-- --------------------------------------------------------
--
-- Table structure for table `posts`
--
CREATE TABLE IF NOT EXISTS `posts` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`title` varchar(250) COLLATE utf8_unicode_ci NOT NULL,
`body` longtext COLLATE utf8_unicode_ci NOT NULL,
`published` datetime NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=1 ;
-- --------------------------------------------------------
--
-- Table structure for table `products`
--
CREATE TABLE IF NOT EXISTS `products` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`category_id` int(11) DEFAULT NULL,
`name` varchar(100) COLLATE utf8_unicode_ci NOT NULL,
`price` decimal(10,0) NOT NULL,
`description` longtext COLLATE utf8_unicode_ci NOT NULL,
PRIMARY KEY (`id`),
KEY `IDX_B3BA5A5A12469DE2` (`category_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=1 ;
-- --------------------------------------------------------
--
-- Table structure for table `User`
--
CREATE TABLE IF NOT EXISTS `User` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`first_name` varchar(150) NOT NULL,
`last_name` varchar(150) NOT NULL,
`sex` tinyint(1) DEFAULT NULL,
`date_of_birth` datetime DEFAULT NULL,
`education` varchar(10) NOT NULL,
`mobile` varchar(10) NOT NULL,
`email` varchar(100) NOT NULL,
`address` varchar(200) NOT NULL,
`status` tinyint(1) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ;
--
-- Dumping data for table `User`
--
INSERT INTO `User` (`id`, `first_name`, `last_name`, `sex`, `date_of_birth`, `education`, `mobile`, `email`, `address`, `status`) VALUES
(1, 'Veerpartap', 'Singh', 1, '2008-11-24 00:00:00', 'MCA', '71505897', 'metveerpartapsingh#gmail.com', 'hl 99 phase 2 sas nagar mohali', 1),
(2, 'Vicky', 'Sharma', 1, '2008-05-09 00:00:00', 'MCA', '88754257', 'vicky.sharma#gmail.com', 'Village Burari, Jila Nawanshar', 1);
--
-- Constraints for dumped tables
--
--
-- Constraints for table `products`
--
ALTER TABLE `products`
ADD CONSTRAINT `FK_B3BA5A5A12469DE2` FOREIGN KEY (`category_id`) REFERENCES `category` (`id`);
/****************************************************************************/

Answer 1

As stated in the above comment, the issue was about that I am not including the Arrarycollection namespace in the controller file. But after including the namespace I get another error while adding new products.
Below is the error message :
"__toString()" method was not foudn on the object of type Main\BlogBundle\Enity\Category to the choice field.
For this error, We need to add a __toString() method to your Category entity. For example:
public function __toString() { return $this->name; }
The PHP magic-method __toString() is used to present a textual representation of the object. In this case, the Category name will be used when selecting a Category in a Form of a related entity.

Answer 2

if you getthe __toString() error in a class XxxxxType extends AbstractType
you can add the fiel definition in the builder, like this. No need to modify your entity.
$builder
->add('enquete','entity',array('class' => 'AdequatSipBundle:Enquete',
'property' => 'Id', 'read_only'=>true))
->add('produit','entity',array('class' => 'AdequatSipBundle:Produit',
'property' => 'Name', 'read_only'=>true))