rails开发 之 active record

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How to use new_record?, changed? and persisted? methods in rails in this example

参考： https://stackoverflow.com/a/50512456

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# new_record?

car = Car.new # => initialize a new Car object
Car.new_record? # => true

# persisted?

car.save
car.persisted? # => true

# changed?

car.model = 'New release model S'
car.changed? # => true

# destroyed?

car.destroy
car.destroyed? # => true