One to One Relationship embed form

gistfile1.txt

Im getting this error:

 Notice: Undefined index: userId in /var/www/html/symfony2/vendor/doctrine/orm/lib/Doctrine/ORM/Persisters/BasicEntityPersister.php line 688 


class UsersType extends AbstractType
{
    /**
     * @param FormBuilderInterface $builder
     * @param array $options
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('username')
            ->add('password')
            ->add('user', new UserFieldsType())
        ;
    }

gistfile2.txt

Acme\DemoBundle\Entity\Users:
    type: entity
    table: users
    uniqueConstraints:
        user_id_UNIQUE:
            columns:
                - user_id
    id:
        user_id:
            type: integer
            generator:
                strategy: AUTO
    fields:
        username:
            type: text
            nullable: true
            length: null
            fixed: false
            comment: ''
        password:
            type: text
            nullable: true
            length: null
            fixed: false
            comment: ''
    oneToOne:
        user:
            targetEntity: UserFields
            cascade:
                - all
            mappedBy: null
            inversedBy: null
            joinColumns:
                user_id:
                    referencedColumnName: user_id
            orphanRemoval: false
    lifecycleCallbacks: {  }

gistfile3.txt

Acme\DemoBundle\Entity\UserFields:
    type: entity
    table: user_fields
    uniqueConstraints:
        user_id_UNIQUE:
            columns:
                - user_id
    id:
        id:
            type: integer
            nullable: false
            unsigned: false
            comment: ''
            id: true
            generator:
                strategy: IDENTITY
    fields:
        userId:
            type: integer
            nullable: true
            unsigned: false
            comment: ''
            column: user_id
        age:
            type: text
            nullable: true
            length: null
            fixed: false
            comment: ''
    lifecycleCallbacks: {  }