fix(model): make diffIndexes() avoid trying to drop default timeseries collection index

lib/helpers/indexes/isTimeseriesIndex.js

@@ -0,0 +1,16 @@
+'use strict';
+
+/**
+ * Returns `true` if the given index matches the schema's `timestamps` options
+ */
+
+module.exports = function isTimeseriesIndex(dbIndex, schemaOptions) {
+  if (schemaOptions.timeseries == null) {
+    return false;
+  }
+  const { timeField, metaField } = schemaOptions.timeseries;
+  if (typeof timeField !== 'string' || typeof metaField !== 'string') {
+    return false;
+  }
+  return Object.keys(dbIndex.key).length === 2 && dbIndex.key[timeField] === 1 && dbIndex.key[metaField] === 1;
+};

lib/model.js

@@ -51,6 +51,7 @@ const immediate = require('./helpers/immediate');
 const internalToObjectOptions = require('./options').internalToObjectOptions;
 const isDefaultIdIndex = require('./helpers/indexes/isDefaultIdIndex');
 const isIndexEqual = require('./helpers/indexes/isIndexEqual');
+const isTimeseriesIndex = require('./helpers/indexes/isTimeseriesIndex');
 const {
   getRelatedDBIndexes,
   getRelatedSchemaIndexes
@@ -1418,6 +1419,10 @@ function getIndexesToDrop(schema, schemaIndexes, dbIndexes) {
     if (isDefaultIdIndex(dbIndex)) {
       continue;
     }
+    // Timeseries collections have a default index on { timeField: 1, metaField: 1 }.
+    if (isTimeseriesIndex(dbIndex, schema.options)) {
+      continue;
+    }
 
     for (const [schemaIndexKeysObject, schemaIndexOptions] of schemaIndexes) {
       const options = decorateDiscriminatorIndexOptions(schema, clone(schemaIndexOptions));
@@ -1429,9 +1434,11 @@ function getIndexesToDrop(schema, schemaIndexes, dbIndexes) {
       }
     }
 
-    if (!found) {
-      toDrop.push(dbIndex.name);
+    if (found) {
+      continue;
     }
+
+    toDrop.push(dbIndex.name);
   }
 
   return toDrop;

test/model.test.js

@@ -8147,6 +8147,52 @@ describe('Model', function() {
       assert.ok(obj.post.updatedAt.valueOf(), new Date('2023-06-01T18:00:00.000Z').valueOf());
     });
   });
+
+  describe('diffIndexes()', function() {
+    it('avoids trying to drop timeseries collections (gh-14984)', async function() {
+      const version = await start.mongodVersion();
+      if (version[0] < 5) {
+        this.skip();
+        return;
+      }
+
+      const schema = new mongoose.Schema(
+        {
+          time: {
+            type: Date
+          },
+          deviceId: {
+            type: String
+          }
+        },
+        {
+          timeseries: {
+            timeField: 'time',
+            metaField: 'deviceId',
+            granularity: 'seconds'
+          },
+          autoCreate: false
+        }
+      );
+
+      const TestModel = db.model(
+        'TimeSeriesTest',
+        schema,
+        'gh14984'
+      );
+
+      await db.dropCollection('gh14984').catch(err => {
+        if (err.codeName === 'NamespaceNotFound') {
+          return;
+        }
+        throw err;
+      });
+      await TestModel.createCollection();
+
+      const { toDrop } = await TestModel.diffIndexes();
+      assert.deepStrictEqual(toDrop, []);
+    });
+  });
 });