Add a cursor for the current page. (#43)

* Add a cursor for the current page.

* add a line in CHANGELOG

* fix Changelog

* add for mongo view

* Update CHANGELOG.md

Co-authored-by: Daniel (dB.) Doubrovkine <[email protected]>

* minor change

* try to fix specs on CI

* Update README.md

Co-authored-by: Daniel (dB.) Doubrovkine <[email protected]>

* remove extra spaces in the README

---------

Co-authored-by: Daniel (dB.) Doubrovkine <[email protected]>

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 * [#38](https://github.com/mongoid/mongoid-scroll/pull/38): Add `previous_cursor` - [@GCorbel](https://github.com/GCorbel).
 * [#42](https://github.com/mongoid/mongoid-scroll/pull/42): Add `first_cursor` - [@GCorbel](https://github.com/GCorbel).
+* [#43](https://github.com/mongoid/mongoid-scroll/pull/43): Add `current_cursor` - [@GCorbel](https://github.com/GCorbel).
 * Your contribution here.
 
 ### 1.0.1 (2023/03/15)

README.md

@@ -95,7 +95,7 @@ Feed::Item.desc(:position).limit(5).scroll(saved_iterator.previous_cursor) do |r
 end
 ```
 
-Use `saved_iterator.first_cursor` to loop over the first records.
+Use `saved_iterator.first_cursor` to loop over the first records or `saved_iterator.current_cursor` to loop over the same records again.
 
 The iteration finishes when no more records are available. You can also finish iterating over the remaining records by omitting the query limit.
 
@@ -161,7 +161,7 @@ end
 
 ## Cursors
 
-You can use `Mongoid::Scroll::Cursor.from_record` to generate a cursor. A cursor points at the last record of the previous iteration and unlike MongoDB cursors will not expire.
+You can use `Mongoid::Scroll::Cursor.from_record` to generate a cursor. A cursor points at the last record of the iteration and unlike MongoDB cursors will not expire.
 
 ```ruby
 record = Feed::Item.desc(:position).limit(3).last

lib/mongo/scrollable.rb

@@ -41,11 +41,14 @@ def scroll(cursor_or_type = nil, options = nil, &_block)
       # scroll
       if block_given?
         previous_cursor = nil
+        current_cursor = nil
         records.each do |record|
           previous_cursor ||= cursor_type.from_record(record, cursor_options.merge(type: :previous))
+          current_cursor ||= cursor_type.from_record(record, cursor_options.merge(include_current: true))
           iterator = Mongoid::Criteria::Scrollable::Iterator.new(
             previous_cursor: previous_cursor,
-            next_cursor: cursor_type.from_record(record, cursor_options)
+            next_cursor: cursor_type.from_record(record, cursor_options),
+            current_cursor: current_cursor
           )
           yield record, iterator
         end

lib/mongoid/criteria/scrollable.rb

@@ -15,11 +15,14 @@ def scroll(cursor_or_type = nil, &_block)
         records = find_records(criteria, cursor)
         if block_given?
           previous_cursor = nil
+          current_cursor = nil
           records.each do |record|
             previous_cursor ||= cursor_from_record(cursor_type, record, cursor_options.merge(type: :previous))
+            current_cursor ||= cursor_from_record(cursor_type, record, cursor_options.merge(include_current: true))
             iterator = Mongoid::Criteria::Scrollable::Iterator.new(
               previous_cursor: previous_cursor,
-              next_cursor: cursor_from_record(cursor_type, record, cursor_options)
+              next_cursor: cursor_from_record(cursor_type, record, cursor_options),
+              current_cursor: current_cursor
             )
             yield record, iterator
           end

lib/mongoid/criteria/scrollable/iterator.rb

@@ -2,10 +2,11 @@ module Mongoid
   class Criteria
     module Scrollable
       class Iterator
-        attr_accessor :previous_cursor, :next_cursor
+        attr_accessor :previous_cursor, :current_cursor, :next_cursor
 
-        def initialize(previous_cursor:, next_cursor:)
+        def initialize(previous_cursor:, current_cursor:, next_cursor:)
           @previous_cursor = previous_cursor
+          @current_cursor = current_cursor
           @next_cursor = next_cursor
         end
 

spec/mongo/collection_view_spec.rb

@@ -127,6 +127,17 @@
                 expect(Mongoid.default_client['feed_items'].find.sort(field_name => 1).limit(2).scroll(second_iterator.previous_cursor, field_type: field_type).to_a).to eq(records.limit(2).to_a)
                 expect(Mongoid.default_client['feed_items'].find.sort(field_name => 1).limit(2).scroll(third_iterator.previous_cursor, field_type: field_type).to_a).to eq(records.skip(2).limit(2).to_a)
               end
+              it 'can loop over the same records with the current cursor' do
+                current_cursor = nil
+                records = Mongoid.default_client['feed_items'].find.sort(field_name => 1)
+                cursor = cursor_type.from_record records.skip(4).first, field_name: field_name, field_type: field_type, include_current: true
+
+                records.limit(2).scroll(cursor, field_type: field_type) do |record, iterator|
+                  current_cursor = iterator.current_cursor
+                end
+
+                expect(records.limit(2).scroll(current_cursor, field_type: field_type).to_a).to eq(records.skip(4).limit(2).to_a)
+              end
               it 'can loop over the first records with the first cursor' do
                 first_cursor = nil
                 records = Mongoid.default_client['feed_items'].find.sort(field_name => 1)

spec/mongoid/criteria_spec.rb

@@ -181,6 +181,16 @@
               expect(Feed::Item.asc(field_name).limit(2).scroll(second_iterator.previous_cursor)).to eq(records.limit(2))
               expect(Feed::Item.asc(field_name).limit(2).scroll(third_iterator.previous_cursor)).to eq(records.skip(2).limit(2))
             end
+            it 'can loop over the same records with the current cursor' do
+              current_cursor = nil
+              cursor = cursor_type.from_record Feed::Item.skip(4).first, field_name: field_name, field_type: field_type, include_current: true
+
+              Feed::Item.asc(field_name).limit(2).scroll(cursor) do |_, iterator|
+                current_cursor = iterator.current_cursor
+              end
+
+              expect(Feed::Item.asc(field_name).limit(2).scroll(current_cursor).to_a).to eq(Feed::Item.asc(field_name).skip(4).limit(2).to_a)
+            end
             it 'can loop over the first records with the first page cursor' do
               first_cursor = nil