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I inherit the _inherit='purchase.order, and create new object with name _name='job.order' and use its view but when i am going to save it showing error (odoo warning) in pic.
Blockquote
I inherit the _inherit='purchase.order, and create new object with name _name='job.order' and use its view but when i am going to save it showing error (odoo warning) in pic.

use _inherits instead of _inherit this way you will create new object with with all field of 'purchase.order plus new field you declare in your model that won't affect original model.