config.yml

# Doctrine Configuration
doctrine:
    orm:
        auto_generate_proxy_classes: "%kernel.debug%"
        entity_managers:
            default:
                mappings:
                    FOSUserBundle: ~
                    SonataMediaBundle: ~
                    ApplicationSonataMediaBundle: ~
                    CoreBundle: ~
                    TadiumPromotionBundle:
                        prefix: 'Tadium\Component\Promotion\Model'

Promotion.xml

<?xml version="1.0" encoding="UTF-8" ?>
<doctrine-mapping
        xmlns="http://doctrine-project.org/schemas/orm/doctrine-mapping"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://doctrine-project.org/schemas/orm/doctrine-mapping
                  http://doctrine-project.org/schemas/orm/doctrine-mapping.xsd"
        xmlns:gedmo="http://gediminasm.org/schemas/orm/doctrine-extensions-mapping">


    <entity name="Tadium\Component\Promotion\Model\Promotion"
            repository-class="Tadium\Bundle\PromotionBundle\Repository\PromotionRepository"
            table="promotion">

        <id name="id" type="integer" column="id">
            <generator strategy="AUTO"/>
        </id>

        <field name="name" column="name" type="string" length="255"/>

        <field name="description" column="description" type="text"/>

        <field name="discount" column="discount" type="decimal" scale="2"/>

        <field name="isActive" column="is_active" type="boolean"/>

        <field name="startsAt" column="starts_at" type="datetime" nullable="true"/>

        <field name="endsAt" column="ends_at" type="datetime" nullable="true"/>

        <field name="createdAt" type="datetime">
            <gedmo:timestampable on="create"/>
        </field>

        <field name="updatedAt" type="datetime">
            <gedmo:timestampable on="update"/>
        </field>

        <one-to-many field="coupons" target-entity="Tadium\Component\Promotion\Model\Coupon"
                     mapped-by="promotion"/>
    </entity>
</doctrine-mapping>

TadiumPromotionBundle.php

<?php

namespace Tadium\Bundle\PromotionBundle;

use Doctrine\ORM\EntityManager;
use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\HttpKernel\Bundle\Bundle;
use Doctrine\Bundle\DoctrineBundle\DependencyInjection\Compiler\DoctrineOrmMappingsPass;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * Class TadiumPromotionBundle
 */
class TadiumPromotionBundle extends Bundle
{
    /**
     * @param ContainerBuilder $container
     */
    public function build(ContainerBuilder $container)
    {
        $this->addRegisterMappingsPass($container);
    }

    /**
     * {@inheritDoc}
     */
    public function boot()
    {
        $this->addEntityNamespace($this->container);
    }

    /**
     * @param ContainerInterface $container
     */
    protected function addEntityNamespace(ContainerInterface $container)
    {
        /** @var \Doctrine\ORM\Configuration $configuration */
        $configuration = $container->get('doctrine')->getManager()->getConfiguration();
        $configuration->addEntityNamespace('TadiumPromotionBundle', 'Tadium\\Component\\Promotion\\Model');
    }

    /**
     * @param ContainerBuilder $container
     */
    protected function addRegisterMappingsPass(ContainerBuilder $container)
    {
        $mappings = [
            realpath(__DIR__ . '/Resources/config/doctrine/model') => 'Tadium\Component\Promotion\Model',
        ];

        $container->addCompilerPass(
            DoctrineOrmMappingsPass::createXmlMappingDriver(
                $mappings,
                ['doctrine.orm.entity_manager']
            )
        );
    }
}