Merge pull request #1171 from transitland/keyset-pagination

Implement keyset pagination
transitland · Aug 22, 2017 · b7c1984 · b7c1984
2 parents 8e83a74 + 95ce2ef
commit b7c1984
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Showing 2 changed files with 33 additions and 3 deletions.
diff --git a/app/controllers/concerns/json_collection_pagination.rb b/app/controllers/concerns/json_collection_pagination.rb
@@ -7,10 +7,10 @@ def paginated_collection(collection)
     per_page = sort_per_page
     offset = sort_offset
     include_total = sort_total
+    min_id = sort_min_id
     meta = {
       sort_key: sort_key,
       sort_order: sort_order,
-      offset: offset,
       per_page: per_page,
     }
     qps = params.permit(query_params.keys)
@@ -22,12 +22,21 @@ def paginated_collection(collection)
     # Setup prev/next links
     if ['false', '∞'].include?(per_page)
       data_on_page = collection.to_a
+    elsif min_id
+      # Get the current page of results, +1 to limit to check next page
+      data = collection.where('id > ?', min_id).limit(per_page+1).to_a
+      data_on_page = data[0...per_page]
+      meta[:sort_min_id] = data_on_page.last.id
+      meta_next = url_for(qps.merge(meta))
+      (meta[:next] = meta_next) if data.size > per_page
     else
       # Get the current page of results.
       #  Add +1 to limit to see if there is a next page.
       #  This will be dropped in the return.
       data = collection.offset(offset).limit(per_page+1).to_a
+      data_on_page = data[0...per_page]
       # Previous and next page
+      meta[:offset] = offset
       meta_prev = url_for(qps.merge(meta).merge({
         offset: (offset - per_page) >= 0 ? (offset - per_page) : 0,
       }))
@@ -36,8 +45,6 @@ def paginated_collection(collection)
       }))
       (meta[:prev] = meta_prev) if offset > 0
       (meta[:next] = meta_next) if data.size > per_page
-      # Slice data
-      data_on_page = data[0...per_page]
     end
 
     if include_total
@@ -74,6 +81,10 @@ def sort_key
     (params[:sort_key].presence || :id).to_sym
   end
 
+  def sort_min_id
+    params[:sort_min_id].presence ? params[:sort_min_id].to_i : nil
+  end
+
   def sort_order
     params[:sort_order].to_s == 'desc' ? :desc : :asc
   end

diff --git a/spec/controllers/json_collection_pagination_spec.rb b/spec/controllers/json_collection_pagination_spec.rb
@@ -84,6 +84,25 @@ def url_for(params)
       })
     end
 
+    it 'sort_min_id' do
+      idx = 1
+      per_page = 5
+      sort_min_id = @issue_ids[idx]
+      next_sort_min_id = @issue_ids[idx+per_page]
+      get :index, sort_min_id: sort_min_id, per_page: per_page
+      expect_json({
+        changesets: -> (changesets) {
+          expect(changesets.map { |i| i[:id] }).to eq(@issue_ids[idx+1...idx+1+per_page])
+        },
+        meta: {
+          sort_key: 'id',
+          sort_order: 'asc',
+          sort_min_id: next_sort_min_id,
+          per_page: per_page
+        }
+      })
+    end
+
     it 'raises ArgumentError on invalid sort_key' do
       expect {
         get :index, sort_key: :unknown_key