From e0b9eed58461769e054fc8d5eac7bf34bdef73be Mon Sep 17 00:00:00 2001
From: Christopher Peplin <chris.peplin@rhubarbtech.com>
Date: Tue, 12 Dec 2023 19:28:34 -0500
Subject: [PATCH] Allow defining index on base model that applies to all
 discriminators

---
 lib/helpers/indexes/getRelatedIndexes.js      |  4 ++-
 .../helpers/indexes.getRelatedIndexes.test.js | 36 +++++++++++++++++++
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/lib/helpers/indexes/getRelatedIndexes.js b/lib/helpers/indexes/getRelatedIndexes.js
index 42d5798c623..b323be84c16 100644
--- a/lib/helpers/indexes/getRelatedIndexes.js
+++ b/lib/helpers/indexes/getRelatedIndexes.js
@@ -46,7 +46,9 @@ function getRelatedIndexes({
 
   return indexes.filter(index => {
     const partialFilterExpression = getPartialFilterExpression(index, indexesType);
-    return !partialFilterExpression || !partialFilterExpression[discriminatorKey];
+    return !partialFilterExpression
+      || !partialFilterExpression[discriminatorKey]
+      || partialFilterExpression[discriminatorKey]['$exists'];
   });
 }
 
diff --git a/test/helpers/indexes.getRelatedIndexes.test.js b/test/helpers/indexes.getRelatedIndexes.test.js
index 3eb597f883d..f6100888de2 100644
--- a/test/helpers/indexes.getRelatedIndexes.test.js
+++ b/test/helpers/indexes.getRelatedIndexes.test.js
@@ -92,6 +92,42 @@ describe('getRelatedIndexes', () => {
         ]
       );
     });
+    it('with base model that has discriminator, it includes discriminator indexes that only checks for existence', () => {
+      // Arrange
+      const eventSchema = new Schema(
+        { actorId: { type: Schema.Types.ObjectId } },
+        { autoIndex: false }
+      );
+      eventSchema.index({ actorId: 1 },
+        { unique: true,
+          partialFilterExpression: {
+            __t: { $exists: true }
+          }
+        });
+
+      const Event = db.model('Event', eventSchema);
+
+      const clickEventSchema = new Schema(
+        {
+          clickedAt: Date,
+          productCategory: String
+        },
+        { autoIndex: false }
+      );
+      Event.discriminator('ClickEvent', clickEventSchema);
+
+      // Act
+      const filteredSchemaIndexes = getRelatedSchemaIndexes(Event, Event.schema.indexes());
+
+      // Assert
+      assert.deepStrictEqual(
+        filteredSchemaIndexes,
+        [
+          [{ actorId: 1 },
+            { background: true, unique: true, partialFilterExpression: { __t: {$exists: true} } }]
+        ]
+      );
+    });
     it('with discriminator model, it only gets discriminator indexes', () => {
       // Arrange
       const eventSchema = new Schema(