class Header{
    /**
     *
     * @ORM\Id
     * @ORM\Column(name="UH1", type="integer", nullable=false)
     */
    protected $key1;

    /**
     *
     * @ORM\Id
     * @ORM\Column(name="UH2", type="integer", nullable=false)
     */
    protected $key2;

    /**
     * @ORM\OneToOne(targetEntity="Detail", mappedBy="header")
     * @ORM\JoinColumns={@ORM\JoinColumn(name="UH1", referencedColumnName="UD1"),
     *                   @ORM\JoinColumn(name="UH2", referencedColumnName="UD2")},
     */
    protected $detail;
}

class Detail{
/**
     *
     * @ORM\Id
     * @ORM\Column(name="UD1", type="integer", nullable=false)
     */
    protected $key1;

    /**
     *
     * @ORM\Id
     * @ORM\Column(name="UD2", type="integer", nullable=false)
     */
    protected $key2;

    /**
     * @ORM\OneToOne(targetEntity="Header", inversedBy="detail")
     * @ORM\JoinColumns={@ORM\JoinColumn(name="UD1", referencedColumnName="UH1"),
     *                   @ORM\JoinColumn(name="UD2", referencedColumnName="UH2")},
     */
    protected $header;
}