Merge pull request #81 from outgrow/outgrow-fix-totalCount-for-aggreg…

…ates Fix `totalCount` on `getPaginatedResponseFromAggregate`
reactioncommerce · Jun 8, 2021 · 58817a8 · 58817a8
2 parents 700bcee + df31453
commit 58817a8
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Showing 2 changed files with 74 additions and 4 deletions.
diff --git a/lib/graphql/getPaginatedResponseFromAggregate.js b/lib/graphql/getPaginatedResponseFromAggregate.js
@@ -39,11 +39,43 @@ async function getPaginatedResponseFromAggregate(collection, pipeline, args, {
   let totalCount = null;
   if (includeTotalCount) {
     pipeline.push({
-      "$addFields": {
+      /**
+       * This stage gathers all of the objects that the pipeline has returned into a single array in one document.
+       * Because we have all the documents in a single array, we can now count them using $sum. Unfortunately the only
+       * way to count the number of returned objects with aggregates, as `.count()` is not available on aggregates.
+       */
+      $group: {
+        _id: null,
+        objects: {
+          $addToSet: "$$ROOT"
+        },
         totalCount: {
-          "$sum": 1
+          $sum: 1
         }
       }
+    }, {
+      /**
+       * Now that we've calculated the total count of objects, we can $unwind our array in our single object to get
+       * individual objects again.
+       */
+      $unwind: {
+        path: "$objects"
+      }
+    }, {
+      /**
+       * Set `totalCount` inside of our objects, since we'll replace the root in the next stage.
+       */
+      $set: {
+        "$objects.totalCount": "$totalCount"
+      }
+    }, {
+      /**
+       * Replace the root. We now have all the objects that were returned by the pipeline originally, but with a new
+       * `totalCount` field in each of them that contains the total count of objects returned.
+       */
+      $replaceRoot: {
+        newRoot: "$objects"
+      }
     });
   }
 

diff --git a/lib/graphql/getPaginatedResponseFromAggregate.test.js b/lib/graphql/getPaginatedResponseFromAggregate.test.js
@@ -56,12 +56,31 @@ test("includes sort param in pipeline and returns correct result", async () => {
         "$someOperator": "someParameter"
       },
       {
-        "$addFields": {
+        "$group": {
+          _id: null,
+          objects: {
+            "$addToSet": "$$ROOT"
+          },
           totalCount: {
             "$sum": 1
           }
         }
       },
+      {
+        $unwind: {
+          path: "$objects"
+        }
+      },
+      {
+        $set: {
+          "$objects.totalCount": "$totalCount"
+        }
+      },
+      {
+        $replaceRoot: {
+          newRoot: "$objects"
+        }
+      },
       {
         "$sort": "SORT"
       },
@@ -84,12 +103,31 @@ test("returns totalCount == 0 when there are no documents", async () => {
         "$someOperator": "someParameter"
       },
       {
-        "$addFields": {
+        "$group": {
+          _id: null,
+          objects: {
+            "$addToSet": "$$ROOT"
+          },
           totalCount: {
             "$sum": 1
           }
         }
       },
+      {
+        $unwind: {
+          path: "$objects"
+        }
+      },
+      {
+        $set: {
+          "$objects.totalCount": "$totalCount"
+        }
+      },
+      {
+        $replaceRoot: {
+          newRoot: "$objects"
+        }
+      },
       {
         "$limit": 20
       }