如何使用new_record ？，变了吗？并坚持吗？本例中的rails中的方法

user2107733 发表于 Dev

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如何，此代码具有以下结果：

 # 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

尝试得出以下结果：

# 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？。要记录更改和新记录的数量。

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*

根据答案的代码：-尝试仅更改1条记录，而不是2条。

# 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

交换

您可以尝试first_or_initialize沿assign_attributes

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

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