service = fields.Many2One('product.product', 'Service',
        required=True, select=True, depends=['service_categories'],
        domain=[
            ('type','=','service'),
            ('category','in',Eval('service_categories')),
            ],
        )

    service_categories = fields.Function(
        fields.One2Many('product.category',None,'All service categories'),
        'get_service_categories')


    def get_service_categories(self,name=''):
        print 'get_service_categories'

        Category = Pool().get('product.category')

        # TODO MODIFY THE CLAUSE
        clause = []
        categories = Category.search(clause)
        return [i.id for i in categories]