With this I get an error by doctrine : "The association Advercity\AdminBundle\Entity\TaxStamp#process refers to the owning side field Advercity\AdminBundle\Entity\Process#taxStamp which does not exist."

Process.php

<?php

/**
 * @ORM\Entity(repositoryClass="ProcessRepository")
 * @ORM\InheritanceType("JOINED")
 * @ORM\DiscriminatorColumn(name="discr", type="string")
 */
class Process
{
  // ...
}

ProcessCadaster.php

<?php

/**
 * @ORM\Entity(repositoryClass="ProcessCadasterRepository")
 */
class ProcessCadaster extends Process implements EntityWithTaxStampInterface
{
  use TaxStampTrait;
  // ...
}

ProcessIdentityCard.php

<?php

/**
 * @ORM\Entity(repositoryClass="ProcessIdentityCardRepository")
 */
class ProcessIdentityCard extends Process implements EntityWithTaxStampInterface
{
  use TaxStampTrait;
  // ...
}

ProcessPassport.php

<?php

/**
 * @ORM\Entity(repositoryClass="ProcessPassportRepository")
 */
class ProcessPassport extends Process implements EntityWithTaxStampInterface
{
  use TaxStampTrait;
  // ...
}

TaxStamp.php

<?php

/**
 * @ORM\Entity(repositoryClass="TaxStampRepository")
 */
class TaxStamp
{
    /**
     * @ORM\OneToOne(targetEntity="Advercity\AdminBundle\Entity\Process", mappedBy="taxStamp")
     */
    private $process;
}

TaxStampTrait.php

<?php

trait TaxStampTrait
{
  /**
   * @ORM\OneToOne(targetEntity="TaxStamp", cascade={"persist"})
   * @ORM\JoinColumn(name="tax_stamp_id", referencedColumnName="id")
   */
  private $taxStamp;
  
  // ...
}