This is not what I want exactly, Your method will give category_id by default based on function. But I want to set type of model.category based on active object(e.g. test.test).

so you can try on_change function based on the change object(test.test) field value model.category value set in the on change method

on change method will be called while I enter some value in some field. If I directly create record, and then create category from test.test default type should come. Is it possible to do ? For example: Create product, then create Contract from product form, by default employee should come as Administrator.

Thanks Prakash, great example!