fix: handle casting $or within $elemMatch

Fix #13974

Author: vkarpov15

lib/schema/array.js

@@ -623,8 +623,8 @@ function cast$elemMatch(val, context) {
       discriminators[val[discriminatorKey]] != null) {
     return cast(discriminators[val[discriminatorKey]], val, null, this && this.$$context);
   }
-
-  return cast(this.casterConstructor.schema, val, null, this && this.$$context);
+  const schema = this.casterConstructor.schema ?? context.schema;
+  return cast(schema, val, null, this && this.$$context);
 }
 
 const handle = SchemaArray.prototype.$conditionalHandlers = {};

test/model.query.casting.test.js

@@ -754,7 +754,7 @@ describe('model query casting', function() {
         assert.strictEqual(doc.outerArray[0].innerArray[0], 'onetwothree');
       });
   });
-  it('should not throw a cast error when dealing with an array of an array of strings in combination with $elemMach and $not (gh-13880)', async function() {
+  it('should not throw a cast error when dealing with an array of an array of strings in combination with $elemMatch and $not (gh-13880)', async function() {
     const testSchema = new Schema({
       arr: [[String]]
     });
@@ -766,6 +766,31 @@ describe('model query casting', function() {
     assert(res);
     assert(res[0].arr);
   });
+  it('should not throw a cast error when dealing with an array of objects in combination with $elemMatch (gh-13974)', async function() {
+    const testSchema = new Schema({
+      arr: [Object]
+    });
+
+    const Test = db.model('Test', testSchema);
+    const obj1 = new Test({ arr: [{ id: 'one' }, { id: 'two' }] });
+    await obj1.save();
+
+    const obj2 = new Test({ arr: [{ id: 'two' }, { id: 'three' }] });
+    await obj2.save();
+
+    const obj3 = new Test({ arr: [{ id: 'three' }, { id: 'four' }] });
+    await obj3.save();
+
+    const res = await Test.find({
+      arr: {
+        $elemMatch: {
+          $or: [{ id: 'one' }, { id: 'two' }]
+        }
+      }
+    }).sort({ _id: 1 });
+    assert.ok(res);
+    assert.deepStrictEqual(res.map(doc => doc.arr[1].id), ['two', 'three']);
+  });
 });
 
 function _geojsonPoint(coordinates) {