Add decorator functionality

.rubocop.yml

@@ -3,7 +3,7 @@ AllCops:
   NewCops: enable
 
 Metrics/AbcSize:
-  Max: 25
+  Max: 30
 
 # DSLs inheritly uses long blocks, like describe and contexts in RSpec,
 # therefore disable this rule for specs and for the gemspec file
@@ -13,22 +13,22 @@ Metrics/BlockLength:
   - spec/**/*
 
 Metrics/ClassLength:
-  Max: 200
+  Max: 205
 
 Metrics/CyclomaticComplexity:
   Max: 15
 
 Metrics/MethodLength:
-  Max: 25
+  Max: 30
 
 Metrics/ParameterLists:
-  Max: 7
+  Max: 8
 
 Metrics/PerceivedComplexity:
-  Max: 13
+  Max: 14
 
 Layout/LineLength:
-  Max: 80
+  Max: 95
 
 Naming/VariableNumber:
   EnforcedStyle: snake_case

lib/rails_cursor_pagination/paginator.rb

@@ -42,15 +42,19 @@ class InvalidCursorError < ParameterError; end
     #   ```
     # @param order [Symbol, nil]
     #   Ordering to apply, either `:asc` or `:desc`. Defaults to `:asc`.
+    # @param record_decorator [Object, proc { |obj| obj.itself }]
+    #   Object to which each paginated record will be passed to. Default behavior
+    #   simply returns the record itself. Object must be callable.
     #
     # @raise [RailsCursorPagination::Paginator::ParameterError]
     #   If any parameter is not valid
     def initialize(relation, first: nil, after: nil, last: nil, before: nil,
-                   order_by: nil, order: nil)
+                   order_by: nil, order: nil, record_decorator: :itself.to_proc)
       order_by ||= :id
       order ||= :asc
 
-      ensure_valid_params!(relation, first, after, last, before, order)
+      ensure_valid_params!(relation, first, after, last, before, order,
+                           record_decorator)
 
       @order_field = order_by
       @order_direction = order
@@ -64,6 +68,8 @@ def initialize(relation, first: nil, after: nil, last: nil, before: nil,
         last ||
         RailsCursorPagination::Configuration.instance.default_page_size
 
+      @record_decorator = record_decorator
+
       @memos = {}
     end
 
@@ -99,10 +105,12 @@ def fetch(with_total: false)
     #   Optional, cannot be combined with `after`
     # @param order [Symbol]
     #   Optional, must be :asc or :desc
+    # @param record_decorator [Object, proc { |obj| obj.itself }]
+    #   Optional, must respond to `.call`
     #
     # @raise [RailsCursorPagination::Paginator::ParameterError]
     #   If any parameter is not valid
-    def ensure_valid_params!(relation, first, after, last, before, order)
+    def ensure_valid_params!(relation, first, after, last, before, order, record_decorator)
       unless relation.is_a?(ActiveRecord::Relation)
         raise ParameterError,
               'The first argument must be an ActiveRecord::Relation, but was '\
@@ -127,6 +135,9 @@ def ensure_valid_params!(relation, first, after, last, before, order)
       if last.present? && last.negative?
         raise ParameterError, "`last` cannot be negative, but was `#{last}`"
       end
+      unless record_decorator.respond_to?(:call)
+        raise ParameterError, '`record_decorator` must respond to .call'
+      end
 
       true
     end
@@ -143,15 +154,16 @@ def page_info
       }
     end
 
-    # Get the records for the given page along with their cursors
+    # Get the records for the given page along with their cursors.
+    # Returned data will have been passed to record_decorator.
     #
     # @return [Array<Hash>] List of hashes, each with a `cursor` and `data`
     def page
       memoize :page do
         records.map do |item|
           {
             cursor: cursor_for_record(item),
-            data: item
+            data: @record_decorator.call(item)
           }
         end
       end
@@ -393,9 +405,7 @@ def relation_with_cursor_fields
 
       relation = @relation
 
-      unless @relation.select_values.include?(:id)
-        relation = relation.select(:id)
-      end
+      relation = relation.select(:id) unless @relation.select_values.include?(:id)
 
       if custom_order_field? && !@relation.select_values.include?(@order_field)
         relation = relation.select(@order_field)

spec/rails_cursor_pagination/paginator_spec.rb

@@ -124,6 +124,13 @@
         include_examples 'for a ParameterError with the right message',
                          '`last` cannot be negative, but was `-4`'
       end
+
+      context 'passing an invalid `record_decorator`' do
+        let(:params) { super().merge(record_decorator: 'no') }
+
+        include_examples 'for a ParameterError with the right message',
+                         '`record_decorator` must respond to .call'
+      end
     end
   end
 
@@ -274,6 +281,28 @@
           expect(subject[:total]).to eq expected_total
         end
       end
+
+      context 'when passing a valid proc as `&record_decorator`' do
+        let(:params) { { record_decorator: :class.to_proc } }
+
+        it 'returns decorated records' do
+          expect(subject[:page].pluck(:data)).to all be Post
+        end
+      end
+
+      context 'when passing a valid lambda as `&record_decorator`' do
+        let(:id_incrementer) { ->(item) { { next_id: item.id + 1 } } }
+        let(:params) { super().merge(record_decorator: id_incrementer) }
+        let(:expected_decorated_response) do
+          expected_posts.map do |post|
+            id_incrementer.call(post)
+          end
+        end
+
+        it 'returns decorated records' do
+          expect(subject[:page].pluck(:data)).to eq expected_decorated_response
+        end
+      end
     end
 
     shared_examples_for 'a well working query that also supports SELECT' do