ruby-on-rails - 如何使用new_record？，改变了？并坚持？本例中 Rails 中的方法

Question

试图理解new record? , changed ?和 persisted ?在下面的例子中。

如何，这段代码有这样的结果:

 # NOW
 # there is 0 new record after running new_data array
 # there is 0 changed record(s) after running new_data array
 # there is 3 persisted record(s) after running new_data array

试图得出这样的结果:

# WANT
#there is 1 new record(s) after running new_data array
#there is 1 changed record(s) after running new_data array
#there is 2 persisted record(s) after running new_data array

*问题是:*

怎么做？想记录更改和新增记录的数量。

Cars.delete_all

original_data = [
    {:brand => 'Mercedes', :used => false, :year => 2000 },
    {:brand => 'Honda',    :used => true , :year => 2000 },
    {:brand => 'Nissan',   :used => false, :year => 2000 }
]

new_data = [
    # updating year to 2013
    {:brand => 'Mercedes', :used => false, :year => 2013 },
    # new record
    {:brand => 'Tesla', :used => false, :year => 2013  },
    # same data
    {:brand => 'Nissan', :used => false, :year => 2000 }
]


# create new cars
original_data.each do |c|
  Cars.create(c)
end

# updates
persisted =   0
new_records = 0
changed_records = 0
new_data.each do |c|
 car =  Cars.where(:brand => c[:brand]).first_or_create
 persisted   +=1 if car.persisted?
 new_records +=1 if car.new_record?
 changed_records +=1 if car.changed?
end

puts "there is #{new_records} new record(s) after running new_data array"
puts "there is #{changed_records} changed record(s) after running new_data array"
puts "there is #{persisted} persisted record(s) after running new_data array"

---

*更新*

代码根据答案:- 尝试仅更改 1 条记录，而不是 2 条记录。

# updates
persisted =   0
new_records = 0
changed_records = 0
new_data.each do |c|
 car =  Cars.where(:brand => c[:brand]).first_or_initialize
 car.assign_attributes(c)
 persisted   +=1 if car.persisted?
 new_records +=1 if car.new_record?
 changed_records +=1 if car.changed?
 car.save
end

there is 1 new record(s) after running new_data array
there is 2 changed record(s) after running new_data array
there is 2 persisted record(s) after running new_data array

Answer 1

我可能不会直接回答您的问题，但我会尝试解释 Activerecord 生命周期方法。

new_record?

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

坚持？

car.save
car.persisted? # => true

改变了吗？

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

毁了？

car.destroy
car.destroyed? # => true