fix: address code review comments

Author: vkarpov15

lib/model.js

@@ -5009,8 +5009,7 @@ Model.recompileSchema = function recompileSchema() {
     }
   }
 
-  const overwriteExisting = true;
-  applyEmbeddedDiscriminators(this.schema, new WeakSet(), overwriteExisting);
+  applyEmbeddedDiscriminators(this.schema, new WeakSet(), true);
 };
 
 /**

test/model.test.js

@@ -7432,28 +7432,31 @@ describe('Model', function() {
 
     // Define discriminated class before model is compiled
     class Deco1 extends Decorator { whoAmI() { return 'I am Test1'; }}
-    const deco1Schema = new Schema({}).loadClass(Deco1);
+    const deco1Schema = new Schema({});
     deco1Schema.loadClass(Deco1);
     decoratorSchema.discriminator('Test1', deco1Schema);
 
     // Define model that uses discriminated schema
     const shopSchema = new Schema({
       item: { type: decoratorSchema, required: true }
     });
-
-    class Shop {}
-    shopSchema.loadClass(Shop);
     const shopModel = db.model('Test', shopSchema);
 
     // Define another discriminated class after the model is compiled
     class Deco2 extends Decorator { whoAmI() { return 'I am Test2'; }}
-    const deco2Schema = new Schema({}).loadClass(Deco2);
+    const deco2Schema = new Schema({});
     deco2Schema.loadClass(Deco2);
     decoratorSchema.discriminator('Test2', deco2Schema);
 
+    let instance = new shopModel({ item: { type: 'Test1' } });
+    assert.equal(instance.item.whoAmI(), 'I am Test1');
+
+    instance = new shopModel({ item: { type: 'Test2' } });
+    assert.equal(instance.item.whoAmI(), 'I am BaseDeco');
+
     shopModel.recompileSchema();
 
-    let instance = new shopModel({ item: { type: 'Test1' } });
+    instance = new shopModel({ item: { type: 'Test1' } });
     assert.equal(instance.item.whoAmI(), 'I am Test1');
 
     instance = new shopModel({ item: { type: 'Test2' } });