Can this Ruby on Rails code be optimized or improved at all?

Question

The code:

user = ... #pretend it has a value :)
instances = Array.new
Product.all.each do |product|
    productInstance = ProductInstance.new
    productInstance.user = user
    productInstance.product = product
    instances.push(productInstance)
end

Product and ProductInstance are both Rails models. Is a for-each loop on Product.all going to be slow? Just wondering if there is a better way of doing this...

Answer 1

Never iterate on your whole collection at one time.

Maybe this will work fine on your development box, and maybe on you fresh production.

But when your application gets popular and your DB will have serious amount of records, you will get time and memory problems with your code.

Use for example http://apidock.com/rails/ActiveRecord/Batches/ClassMethods/find_in_batches and learn how garbage collection works http://timetobleed.com/garbage-collection-slides-from-la-ruby-conference/

Product.find_in_batches do |products|
  products.each do |product|
    productInstance = ProductInstance.new
    productInstance.user = user
    productInstance.product = product
    instances.push(productInstance)  
  end
end

Answer 2

I'd only change each to map (it's more idiomatic).

instances = Product.all.map do |product|
    productInstance = ProductInstance.new
    productInstance.user = user
    productInstance.product = product
    productInstance
end

Answer 3

Somthing like this should work.

instances = Product.all.map do |product|
    productInstance = ProductInstance.new(:user => user,:product => product)
end

or even

instances = Product.all.map do |product|
    ProductInstance.new(:user => user,:product => product)
end

For Mass assignment restriction you can try something like

instances = Product.all.map do |product|
    ProductInstance.new {|instance| instance.user = user;instance.product = product}
end

Answer 4

first in your ProductInstance model add

attr_accessible :user, :product 

and then

instances = Product.all.map {|product| ProductInstance.create(:user => user, :product => product)}

should work.

Answer 5

也可以这样做

 instances = Product.all.map {|product| ProductInstance.new(:user => user, :product => product)}