Reflect the latest changes of Symfony2 and Doctrine2's Annotations (http://bit.ly/cGZbjw)

User.php

<?php

namespace Application\MyBundle\Entity;

use Doctrine\Common\Collections\ArrayCollection;

/**
 * @orm:Entity(repositoryClass="Application\MyBundle\Entity\UserRepository")
 * @orm:Table(name="user",
 *     uniqueConstraints={
 *         @orm:UniqueConstraint(name="username_idx", columns={"username"}),
 *         @orm:UniqueConstraint(name="email_idx", columns={"email"})
 *     }
 * )
 * @orm:HasLifecycleCallbacks
 */
class User
{
    /**
     * @orm:Column(name="id", type="integer")
     * @orm:Id
     * @orm:GeneratedValue(strategy="AUTO")
     * @var integer
     */
    protected $id;

    /**
     * @orm:Column(name="username", type="string", length="32")
     * @validation:Min(3)
     * @validation:Max(32)
     * @validation:NotBlank
     * @var string
     */
    protected $username;

    /**
     * @orm:Column(name="email", type="string", length="256")
     * @validation:Email
     * @validation:NotBlank
     * @var string
     */
    protected $email;

    /**
     * @orm:Column(name="password", type="string", length="32")
     * @validation:NotBlank
     * @var string
     */
    protected $password;

    /**
     * @orm:Column(name="activation_key", type="string", length="32")
     * @var \DateTime
     */
    protected $activationKey;

    /**
     * @orm:Column(name="activation", type="datetime", nullable="true")
     * @var \DateTime
     */
    protected $activation;

    /**
     * @orm:Column(name="last_login", type="datetime", nullable="true")
     * @var \DateTime
     */
    protected $lastLogin;

    /**
     * @orm:Column(type="datetime")
     * @validation:NotBlank
     * @var \DateTime
     */
    protected $created;

    /**
     * @orm:Column(type="datetime")
     * @validation:NotBlank
     * @var \DateTime
     */
    protected $updated;

    /**
     * Constructor.
     */
    public function __construct()
    {
        $this->created = $this->updated = new \DateTime('now');
    }

    /**
     * @return integer
     */
    public function getId()
    {
        return $this->id;
    }

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

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

    /**
     * @param string $username
     */
    public function setUsername($username)
    {
        $this->username = $username;
    }

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

    /**
     * @param string $email
     */
    public function setEmail($email)
    {
        $this->email = $email;
    }

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

    /**
     * @param string $password
     */
    public function setPassword($password)
    {
        $this->password = md5($password);
    }

    /**
     * @param string $password
     * @return boolean
     */
    public function checkPassword($password)
    {
        return md5($password) == $this->password;
    }

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

    /**
     * @param string $activationKey
     */
    public function setActivationKey($activationKey)
    {
        $this->activationKey = $activationKey;
    }

    /**
     * @return string
     */
    public function generateActivationKey()
    {
        return md5(sprintf('%s_%d_%s_%f',
            $this->getUsername(),
            rand(0, 99999),
            $this->getEmail(),
            microtime(true)
        ));
    }

    /**
     * @return \DateTime
     */
    public function getActivation()
    {
        return $this->activation;
    }

    /**
     * @param \DateTime $activation
     */
    public function setActivation(\DateTime $activation)
    {
        $this->activation = $activation;
    }

    /**
     * @return \DateTime
     */
    public function isActivated()
    {
        return (boolean) $this->activation;
    }

    /**
     * @return \DateTime
     */
    public function getLastLogin()
    {
        return $this->lastLogin;
    }

    /**
     * @param \DateTime $lastLogin
     */
    public function setLastLogin(\DateTime $lastLogin)
    {
        $this->lastLogin = $lastLogin;
    }

    /**
     * @return \DateTime
     */
    public function getLast_login()
    {
        return $this->lastLogin;
    }

    /**
     * @param \DateTime $last_login
     */
    public function setLast_login(\DateTime $last_login)
    {
        $this->lastLogin = $last_login;
    }

    /**
     * @return \DateTime
     */
    public function getCreated()
    {
        return $this->created;
    }

    /**
     * @param \DateTime $created
     */
    public function setCreated(\DateTime $created)
    {
        $this->created = $created;
    }

    /**
     * @return \DateTime
     */
    public function getUpdated()
    {
        return $this->updated;
    }

    /**
     * @param \DateTime $updated
     */
    public function setUpdated(\DateTime $updated)
    {
        $this->updated = $updated;
    }

    /**
     * @orm:PreUpdate
     */
    public function update()
    {
        $this->updated = new \DateTime('now');
    }
}