My Rant

Sadly, this isn’t really documented (at time of writing).

Adding new protected variables to your User.php entity will not actually create database entries when you try to do a doctrine:schema:update.

While one still needs to have the protected variables in this entity class, along with getters and setters, the actual creation work is within UserBundle/Resources/config/doctrine/User.orm.xml

Here is an example for adding a foreign key:

<?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">

    <entity name="Application\Sonata\UserBundle\Entity\User" table="fos_user_user">

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

        <many-to-one field="client" target-entity="Myvendor\MyBundle\Entity\Client" orphan-removal="">
            <join-columns>
                <join-column name="client_id" referenced-column-name="id" nullable="1"/>
            </join-columns>
        </many-to-one>

    </entity>

</doctrine-mapping>