Rapsys\UserBundle\Entity\Group:
    type: mappedSuperclass
#   table: groups
    id:
        id:
            type: integer
            generator: 
                strategy: AUTO
            options:
                unsigned: true
    fields:
        title:
            type: string
            length: 16
        created:
            type: datetime
        updated:
            type: datetime
#    manyToMany:
#        users:
#            targetEntity: User
#            mappedBy: groups
    lifecycleCallbacks:
        preUpdate: ['preUpdate']