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

Question

Trying to undestand new record?,changed ? and persisted ? on the example below.

How, this code has this result:

 # 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

Trying to come to this result:

# 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

*Question is: *

How to do it?. Want to record the number of changed and new records.

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"

---

*UPDATE*

code according to answer: - attempt to change only 1 record, not 2.

# 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

Solution 1

You can try first_or_initialize along with 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

Solution 2

I might not answer your question directly but I will try explain the Activerecord lifecyle methods.

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

Comments

[NBSamar]

Car.new_record?, here we need to check for Car's instance, which is stored in car variable here. So, the correct way would be car.new_record?

[Kaka Ruto]

You were right @NBSamar. Updated!