fix(update): support updating array embedded discriminator props if d…

…iscriminator key in $elemMatch

Fix #8063

lib/helpers/query/getEmbeddedDiscriminatorPath.js

@@ -22,21 +22,29 @@ module.exports = function getEmbeddedDiscriminatorPath(schema, update, filter, p
     if (schematype == null) {
       continue;
     }
+
     type = schema.pathType(subpath);
     if ((schematype.$isSingleNested || schematype.$isMongooseDocumentArrayElement) &&
         schematype.schema.discriminators != null) {
       const discriminators = schematype.schema.discriminators;
-      const discriminatorValuePath = subpath + '.' +
-        get(schematype, 'schema.options.discriminatorKey');
+      const key = get(schematype, 'schema.options.discriminatorKey');
+      const discriminatorValuePath = subpath + '.' + key;
       const discriminatorFilterPath =
         discriminatorValuePath.replace(/\.\d+\./, '.');
       let discriminatorKey = null;
+
       if (discriminatorValuePath in filter) {
         discriminatorKey = filter[discriminatorValuePath];
       }
       if (discriminatorFilterPath in filter) {
         discriminatorKey = filter[discriminatorFilterPath];
       }
+      const wrapperPath = subpath.replace(/\.\d+$/, '');
+      if (schematype.$isMongooseDocumentArrayElement &&
+          get(filter[wrapperPath], '$elemMatch.' + key) != null) {
+        discriminatorKey = filter[wrapperPath].$elemMatch[key];
+      }
+
       if (discriminatorKey == null || discriminators[discriminatorKey] == null) {
         continue;
       }