Django admin——如何根据其他模型字段值计算字段值。

I have this scenario: A Service repair that might include repair/installation of multiple spare Parts in a machine. For every spare part involved in the service repair, the technician can select its state (new, used, refurbished). In a separate table called PartCostRate, I map a cost percentage for a state:I have this scenario: A Service repair that mig