I want to create Model (car) name like, Telsa / Model X, and I found this piece of code of Fleet module doing that.

FleetVehicleModel class (models.Model) 
    _name = 'fleet.vehicle.model' 
    _description = 'Model of a vehicle' 
    _order = 'desc' 

    name = fields.Char ('Model name', required = True) 
    brand_id = fields. Many2one ('fleet.vehicle.model.brand', 'Make', required = True, help = 'Make of the vehicle') 
    vendors fields.Many2many = ('res.partner', 'fleet_vehicle_model_vendors',' model_id '' partner_id ', string =' Vendors') 
    image = fields.Binary (related = 'brand_id.image', string = "Logo", readonly = False) 
    image_medium = fields.Binary (related = 'brand_id.image_medium', string = "Logo (medium) ",
    image_small = fields.Binary (related = 'brand_id.image_small', string = "Logo (small)", readonly = False) 

    @ api.multi 
    @ api.depends ('name', 'brand_id') 
    def name_get (self): 
        res = [] 
        for record in self: 
            name = record.name 
            if record.brand_id.name: 
                name = record.brand_id.name + '/' + name 
            res.append ((record.id, name)) 
        return res

I do not understand how this code works when I choose the model then press Save button, it will create a new name under the form "Brand / Model" and replace the old name I filled. 
And I did not see any 'computed field' in this model. 
I figure out by 'print (res)', but I do not understand how this can link 'record.id' in 'res []' to find the new name. 
I also can not find any new fields in Database too.

I will appreciate if someone can explain it. 
Many thanks