一对多双向

这种双向映射需要 OneToMany 关联的 mappedBy 属性和 ManyToOne 关联的 inversedBy 属性。

双向关系既有拥有也有反向 。OneToMany 关系可以使用连接表，因此你必须指定拥有方。OneToMany 关联始终是双向关联的反面。

<?php

namespace AppBundle\Entity;

use Doctrine\ORM\Mapping as ORM;

/**
 * @ORM\Entity
 * @ORM\Table(name="users")
 */
class User
{
    /**
     * @var int
     *
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    protected $id;
     
     /**
     * @var string
     *
     * @ORM\Column(name="username", type="string", length=255)
     */
    protected $username;

    /**
     * @var Group|null
     *
     * @ORM\ManyToOne(targetEntity="AppBundle\Entity\Group", inversedBy="users")
     * @ORM\JoinColumn(name="group_id", referencedColumnName="id", nullable=true)
     */
    protected $group;

    /**
     * @param string $username
     * @param Group|null $group
     */
    public function __construct($username, Group $group = null)
    {
        $this->username = $username;
        $this->group = $group;
    }

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

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

    /**
     * @param Group|null $group
     */
    public function setGroup(Group $group = null)
    {
        if($this->group !== null) {
            $this->group->removeUser($this);
        }

        if ($group !== null) {
            $group->addUser($this);
        }

        $this->group = $group;
    }

    /**
     * Get group
     *
     * @return Group|null
     */
    public function getGroup()
    {
        return $this->group;
    }
}

<?php

namespace AppBundle\Entity;

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

/**
 * @ORM\Entity
 * @ORM\Table(name="groups")
 */
class Group
{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    protected $id;

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

    /**
     * @ORM\OneToMany(targetEntity="AppBundle\Entity\User", mappedBy="group")
     */
    protected $users;

    /**
     * @param string $name
     */
    public function __construct($name)
    {
        $this->name = $name;
        $this->users = new ArrayCollection();
    }

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

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

    public function addUser(User $user)
    {
        if (!$this->getUsers()->contains($user)) {
            $this->getUsers()->add($user);
        }
    }

    public function removeUser(User $user)
    {
        if ($this->getUsers()->contains($user)) {
            $this->getUsers()->removeElement($user);
        }
    }

    public function getUsers()
    {
        return $this->users;
    }

    public function __toString()
    {
        return (string) $this->getName();
    }
}