From d13623ca46c82120c398f4634e206422fc3ad7ea Mon Sep 17 00:00:00 2001
From: David Heinemeier Hansson <david@loudthinking.com>
Date: Mon, 23 Feb 2009 12:10:24 +0100
Subject: Added ActiveRecord::Base.each and ActiveRecord::Base.find_in_batches
 for batch processing [DHH/Jamis Buck]

---
 activerecord/lib/active_record/base.rb    |  2 +-
 activerecord/lib/active_record/batches.rb | 70 +++++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+), 1 deletion(-)
 create mode 100644 activerecord/lib/active_record/batches.rb

(limited to 'activerecord/lib/active_record')

diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 78c6ac2ba8..982342e509 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -3147,7 +3147,7 @@ module ActiveRecord #:nodoc:
     # #save_with_autosave_associations to be wrapped inside a transaction.
     include AutosaveAssociation, NestedAttributes
 
-    include Aggregations, Transactions, Reflection, Calculations, Serialization
+    include Aggregations, Transactions, Reflection, Batches, Calculations, Serialization
   end
 end
 
diff --git a/activerecord/lib/active_record/batches.rb b/activerecord/lib/active_record/batches.rb
new file mode 100644
index 0000000000..7747655984
--- /dev/null
+++ b/activerecord/lib/active_record/batches.rb
@@ -0,0 +1,70 @@
+module ActiveRecord
+  module Batches # :nodoc:
+    def self.included(base)
+      base.extend(ClassMethods)
+    end
+
+    # When processing large numbers of records, it's often a good idea to do so in batches to prevent memory ballooning.
+    module ClassMethods
+      # Yields each record that was found by the find +options+. The find is performed by find_in_batches
+      # with a batch size of 1000 (or as specified by the +limit+ option).
+      #
+      # Example:
+      #
+      #   Person.each(:conditions => "age > 21") do |person|
+      #     person.party_all_night!
+      #   end
+      #
+      # Note: This method is only intended to use for batch processing of large amounts of records that wouldn't fit in
+      # memory all at once. If you just need to loop over less than 1000 records, it's probably better just to use the
+      # regular find methods.
+      def each(options = {})
+        find_in_batches(options) do |records|
+          records.each { |record| yield record }
+        end
+
+        self
+      end
+
+      # Yields each batch of records that was found by the find +options+ as an array. The size of each batch is
+      # set by the +limit+ option; the default is 1000.
+      #
+      # You can control the starting point for the batch processing by supplying the +start+ option. This is especially
+      # useful if you want multiple workers dealing with the same processing queue. You can make worker 1 handle all the
+      # records between id 0 and 10,000 and worker 2 handle from 10,000 and beyond (by setting the +start+ option on that
+      # worker).
+      #
+      # It's not possible to set the order. That is automatically set to ascending on the primary key ("id ASC") 
+      # to make the batch ordering work. This also mean that this method only works with integer-based primary keys.
+      # You can't set the limit either, that's used to control the the batch sizes.
+      #
+      # Example:
+      #
+      #   Person.find_in_batches(:conditions => "age > 21") do |group|
+      #     sleep(50) # Make sure it doesn't get too crowded in there!
+      #     group.each { |person| person.party_all_night! }
+      #   end
+      def find_in_batches(options = {})
+        raise "You can't specify an order, it's forced to be #{batch_order}" if options[:order]
+        raise "You can't specify a limit, it's forced to be the batch_size"  if options[:limit]
+
+        start = options.delete(:start).to_i
+
+        with_scope(:find => options.merge(:order => batch_order, :limit => options.delete(:batch_size) || 1000)) do
+          records = find(:all, :conditions => [ "#{table_name}.#{primary_key} >= ?", start ])
+
+          while records.any?
+            yield records
+            records = find(:all, :conditions => [ "#{table_name}.#{primary_key} > ?", records.last.id ])
+          end
+        end
+      end
+      
+      
+      private
+        def batch_order
+          "#{table_name}.#{primary_key} ASC"
+        end
+    end
+  end
+end
\ No newline at end of file
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