if i have model project that have one or more from model unit , then i have another model that i want to select project then on change the project want to populate the units according to project selection 

example 

have project 1 have units 1,2 ,3 

project 2 have units 1,4,5 

when select project want to populate the units 1,2,3 if changed to project 2 populate  the units 1,4,5

i have written my own code to get the list of related units, just want to know how i can set this list to the units 

here is the code

class rsproject(models.Model):
    _name = 'rs.project'
    units = fields.One2many('rs.unit','name',string ='Units', ondelete='cascade')

class rs_unit(models.Model):
    _name="rs.unit"
project = fields.Many2one('rs.project', ondelete='cascade', string="Project", required=True)

class rsreservation(models.Model):
    _name = 'rs.reservation'
    project = fields.Many2one('rs.project', ondelete='cascade', string="Project", required=True)
    unit = fields.Many2one('rs.unit', ondeletel='cascade', string="Unit Number", required=True)

    @api.one
    @api.onchange('project')
    def on_change_project(self):
	    units_obj = self.pool.get('rs.unit') 
		project_id =  self.project.id
        #get units list according to selected project 		
		unit_list = units_obj.search(self._cr,self._uid,[('id','=',project_id)])
		# what is the correct syntax to set the unit field with unit_list