Fatal error: Uncaught exception 'Doctrine\ORM\Mapping\MappingException' with message 'The column id must be mapped to a field in class Entity\Bar since it is referenced by a join column of another class.' in C:\...\vendor\doctrine\orm\lib\Doctrine\ORM\Mapping\MappingException.php:203
Stack trace:
#0 C:\...\vendor\doctrine\orm\lib\Doctrine\ORM\Persisters\BasicEntityPersister.php(734): Doctrine\ORM\Mapping\MappingException::joinColumnMustPointToMappedField('Entity\Bar', 'id')
#1 C:\...\vendor\doctrine\orm\lib\Doctrine\ORM\UnitOfWork.php(2509): Doctrine\ORM\Persisters\BasicEntityPersister->loadOneToOneEntity(Array, Object(Entity\Bar))
#2 C:\...\vendor\doctrine\orm\lib\Doctrine\ORM\Internal\Hydration\ObjectHydrator.php(245): Doctrine\ORM\UnitOfWork->createEntity('Entity\Bar', Array, Array)
#3 C:\...\vendor\doctrine\orm\lib\Doctrine\ORM\Internal\Hydration\ObjectHydrator.php(424): Doctrine\ORM\Internal\Hydration\Ob in C:\...\vendor\doctrine\orm\lib\Doctrine\ORM\Mapping\MappingException.php on line 203

//Entity/Foo.php

/** @Entity @Table(name="foos") */
class Foo
{
    /** @Id @Column(type="integer") @GeneratedValue */
    protected $id;

    /** @OneToOne(targetEntity="Bar", mappedBy="foo") */
    protected $bar;

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

    public function getBar()
    {
        return $this->bar;
    }

    public function setBar($bar)
    {
        $bar->setFoo($this);
        $this->bar = $bar;
    }
}

//Entity/Bar.php

/** @Entity @Table(name="bars") */
class Bar
{
    /** @Id @OneToOne(targetEntity="Foo", inversedBy="bar")
     * @JoinColumn(name="id", referencedColumnName="id") */
    protected $foo;

    /** @OneToOne(targetEntity="Baz", mappedBy="bar") */
    protected $baz;

    public function __construct($foo)
    {
        $this->foo = $foo;
    }

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

    public function getFoo()
    {
        return $this->foo;
    }

    public function setFoo($foo)
    {
        $this->foo = $foo;
    }

    public function getBaz()
    {
        return $this->baz;
    }

    public function setBaz($baz)
    {
        $bar->setBar($this);
        $this->baz = $baz;
    }
}

//Entity/Baz.php

/** @Entity @Table(name="bazes") */
class Baz
{
    /** @Id @OneToOne(targetEntity="Bar", inversedBy="baz")
     * @JoinColumn(name="id", referencedColumnName="id") */
    protected $bar;

    public function __construct($bar)
    {
        $this->bar = $bar;
    }

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

    public function getBar()
    {
        return $this->bar;
    }

    public function setBar($bar)
    {
        $this->bar = $bar;
    }
}

$fooRepository = $em->getRepository('Entity\Foo');
$foos = $fooRepository->findAll();