Added support for reindexing the index documents into new index

Added a `Tire::Index#reindex` method which uses the "scan/scroll" API to retrieve
documents from index A and import them into index B.

If the new index does not exists, it is created: you may pass settings as an options hash.

You may pass a Tire DSL query as a block to the method.

Example:
--------

    require 'tire'

    Tire.configure { logger STDERR }

    Tire.index('scantest-new') { delete }

    documents = (1..100).map do |i|
      { id: i, type: 'test', title: "Document #{i}" }
    end

    puts "", "Importing data into ElasticSearch..."

    Tire.index 'scantest' do
      delete and create :settings => { :number_of_shards => 1, :number_of_replicas => 0 }
      import documents
      refresh
    end

    Tire.index('scantest').reindex 'scantest-new', settings: { number_of_shards: 3 } do
      query { string '10*' }
    end

lib/tire.rb

@@ -6,6 +6,7 @@
 
 require 'active_support/core_ext/object/to_param'
 require 'active_support/core_ext/object/to_query'
+require 'active_support/core_ext/hash/except.rb'
 
 # Ruby 1.8 compatibility
 require 'tire/rubyext/ruby_1_8' if defined?(RUBY_VERSION) && RUBY_VERSION < '1.9'

lib/tire/index.rb

@@ -129,6 +129,17 @@ def import(klass_or_collection, options={})
       end
     end
 
+    def reindex(name, options={}, &block)
+      new_index = Index.new(name)
+      new_index.create(options) unless new_index.exists?
+
+      Search::Scan.new(self.name, &block).each do |results|
+        new_index.bulk_store results.map do |document|
+          document.to_hash.except(:type, :_index, :_explanation, :_score, :_version, :highlight, :sort)
+        end
+      end
+    end
+
     def remove(*args)
       if args.size > 1
         type, document = args

test/integration/reindex_test.rb

@@ -0,0 +1,46 @@
+require 'test_helper'
+
+module Tire
+
+  class ReindexIntegrationTest < Test::Unit::TestCase
+    include Test::Integration
+
+    context "Reindex" do
+      setup do
+        Tire.index('reindex-test-new').delete
+
+        documents = (1..100).map { |i| { id: i, type: 'test', title: "Document #{i}" } }
+
+        Tire.index 'reindex-test' do
+          delete
+          create :settings => { :number_of_shards => 1, :number_of_replicas => 0 }
+          import documents
+          refresh
+        end
+      end
+
+      teardown do
+        Index.new('reindex-test').delete
+        Index.new('reindex-test-new').delete
+      end
+
+      should "reindex the index into a new index with different settings" do
+        Tire.index('reindex-test').reindex 'reindex-test-new', settings: { number_of_shards: 3 }
+
+        Tire.index('reindex-test-new').refresh
+        assert_equal 100, Tire.search('reindex-test-new').results.total
+        assert_equal '3', Tire.index('reindex-test-new').settings['index.number_of_shards']
+      end
+
+      should "reindex a portion of an index into a new index" do
+        Tire.index('reindex-test').reindex('reindex-test-new') { query { string '10*' } }
+
+        Tire.index('reindex-test-new').refresh
+        assert_equal 2, Tire.search('reindex-test-new').results.total
+      end
+
+    end
+
+  end
+
+end

test/unit/index_test.rb

@@ -720,6 +720,53 @@ def self.count;          DATA.size;        end
 
       end
 
+      context "reindexing" do
+        setup do
+          @results = {
+            "_scroll_id" => "abc123",
+            "took" => 3,
+            "hits" => {
+              "total" => 10,
+              "hits" => [
+                { "_id" => "1", "_source" => { "title" => "Test" } }
+              ]
+            }
+          }
+        end
+
+        should "perform bulk store in the new index" do
+          Index.any_instance.stubs(:exists?).returns(true)
+          Search::Scan.any_instance.stubs(:__perform)
+          Search::Scan.any_instance
+                      .expects(:results)
+                      .returns(Results::Collection.new(@results))
+                      .then
+                      .returns(Results::Collection.new(@results.merge('hits' => {'hits' => []})))
+                      .at_least_once
+
+          Index.any_instance.expects(:bulk_store).once
+
+          @index.reindex 'whammy'
+        end
+
+        should "create the new index if it does not exist" do
+          options = { :settings => { :number_of_shards => 1 } }
+
+          Index.any_instance.stubs(:exists?).returns(false)
+          Search::Scan.any_instance.stubs(:__perform)
+          Search::Scan.any_instance
+                      .expects(:results)
+                      .returns(Results::Collection.new(@results))
+                      .then
+                      .returns(Results::Collection.new(@results.merge('hits' => {'hits' => []})))
+                      .at_least_once
+
+          Index.any_instance.expects(:create).with(options).once
+
+          @index.reindex 'whammy', options
+        end
+
+      end
     end
 
   end