Method: ActiveRecord::Batches#find_each

Defined in:
lib/active_record/relation/batches.rb

#find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, cursor: primary_key, order: DEFAULT_ORDER, &block) ⇒ Object

Looping through a collection of records from the database (using the Scoping::Named::ClassMethods.all method, for example) is very inefficient since it will try to instantiate all the objects at once.

In that case, batch processing methods allow you to work with the records in batches, thereby greatly reducing memory consumption.

The #find_each method uses #find_in_batches with a batch size of 1000 (or as specified by the :batch_size option).

Person.find_each do |person|
  person.do_awesome_stuff
end

Person.where("age > 21").find_each do |person|
  person.party_all_night!
end

If you do not provide a block to #find_each, it will return an Enumerator for chaining with other methods:

Person.find_each.with_index do |person, index|
  person.award_trophy(index + 1)
end

Options

  • :batch_size - Specifies the size of the batch. Defaults to 1000.

  • :start - Specifies the cursor column value to start from, inclusive of the value.

  • :finish - Specifies the cursor column value to end at, inclusive of the value.

  • :error_on_ignore - Overrides the application config to specify if an error should be raised when an order is present in the relation.

  • :cursor - Specifies the column to use for batching (can be a column name or an array of column names). Defaults to primary key.

  • :order - Specifies the cursor column order (can be :asc or :desc or an array consisting of :asc or :desc). Defaults to :asc.

    class Order < ActiveRecord::Base
  self.primary_key = [:id_1, :id_2]
end

Order.find_each(order: [:asc, :desc])

    In the above code, id_1 is sorted in ascending order and id_2 in descending order.

Limits are honored, and if present there is no requirement for the batch size: it can be less than, equal to, or greater than the limit.

The options start and finish are especially useful if you want multiple workers dealing with the same processing queue. You can make worker 1 handle all the records between id 1 and 9999 and worker 2 handle from 10000 and beyond by setting the :start and :finish option on each worker.

# In worker 1, let's process until 9999 records.
Person.find_each(finish: 9_999) do |person|
  person.party_all_night!
end

# In worker 2, let's process from record 10_000 and onwards.
Person.find_each(start: 10_000) do |person|
  person.party_all_night!
end

NOTE: Order can be ascending (:asc) or descending (:desc). It is automatically set to ascending on the primary key (“id ASC”). This also means that this method only works when the cursor column is orderable (e.g. an integer or string).

NOTE: When using custom columns for batching, they should include at least one unique column (e.g. primary key) as a tiebreaker. Also, to reduce the likelihood of race conditions, all columns should be static (unchangeable after it was set).

NOTE: By its nature, batch processing is subject to race conditions if other processes are modifying the database.



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# File 'lib/active_record/relation/batches.rb', line 85

def find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil, cursor: primary_key, order: DEFAULT_ORDER, &block)
  if block_given?
    find_in_batches(start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore, cursor: cursor, order: order) do |records|
      records.each(&block)
    end
  else
    enum_for(:find_each, start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore, cursor: cursor, order: order) do
      relation = self
      cursor = Array(cursor)
      apply_limits(relation, cursor, start, finish, build_batch_orders(cursor, order)).size
    end
  end
end