Hi,

There is only one object "res.partner" which manage customer and supplier.

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Customer, supplier and user (and maybe other 'persons') use the same model 'res.partner'. In order for your model to only do something different for customer, you should ask in your write and your create, if the res.partner you are in, is a customer.

Some quick and dirty code:

def create(.....):
    partner = pool.get(id)
    if partner.is_customer and not partner.supplier:
        do your code here
    else:
        res = super(self, res.partner).create(.....)

The same goes for write.