Rails 4: find all records

Question

According to the Rails Guide on Active Record Query Interface, the correct way to iterate through all records is by using find_each.

Using Foo.all.each will load the entire table into memory, instantiating all the rows; then iterate through the instances. find_each does this in batches, which is more efficient in terms of memory usage.

From the guide:

The find_each method retrieves a batch of records and then yields each record to the block individually as a model. In the following example, find_each will retrieve 1000 records (the current default for both find_each and find_in_batches) and then yield each record individually to the block as a model. This process is repeated until all of the records have been processed:

User.find_each do |user|
  NewsLetter.weekly_deliver(user)
end

References:

• Active Record Query Interface
• ActiveRecord::Batches

yes, Foo.all.

all is deprecated on an ActiveRecord::Relation (eg. Foo.where(true)), not on ActiveRecord::Base.

http://api.rubyonrails.org/classes/ActiveRecord/Scoping/Named/ClassMethods.html#method-i-all

Release notes for Rails 4:

Model.all now returns an ActiveRecord::Relation, rather than an array of records. Use Relation#to_a if you really want an array.

So your code will look like this:

Foo.all.to_a.each do |foo|
  # whatever
end

See http://guides.rubyonrails.org/4_0_release_notes.html#active-record