feat(model): add recompileSchema() function to models to allow appl…

…ying schema changes after compiling

Fix #14296

lib/model.js

@@ -4861,6 +4861,34 @@ Model.__subclass = function subclass(conn, schema, collection) {
   return Model;
 };
 
+/**
+ * Apply changes made to this model's schema after this model was compiled.
+ * By default, adding virtuals and other properties to a schema after the model is compiled does nothing.
+ * Call this function to apply virtuals and properties that were added later.
+ *
+ * #### Example:
+ *     const schema = new mongoose.Schema({ field: String });
+ *     const TestModel = mongoose.model('Test', schema);
+ *     TestModel.schema.virtual('myVirtual').get(function() {
+ *       return this.field + ' from myVirtual';
+ *     });
+ *     const doc = new TestModel({ field: 'Hello' });
+ *     doc.myVirtual; // undefined
+ *
+ *     TestModel.recompileSchema();
+ *     doc.myVirtual; // 'Hello from myVirtual'
+ *
+ * @return {Model}
+ * @api public
+ * @memberOf Model
+ * @static
+ * @method recompileSchema
+ */
+
+Model.recompileSchema = function recompileSchema() {
+  this.prototype.$__setSchema(this.schema);
+};
+
 /**
  * Helper for console.log. Given a model named 'MyModel', returns the string
  * `'Model { MyModel }'`.

test/model.test.js

@@ -7302,6 +7302,19 @@ describe('Model', function() {
       /First argument to `Model` constructor must be an object/
     );
   });
+
+  it('supports recompiling model with new schema additions (gh-14296)', function() {
+    const schema = new mongoose.Schema({ field: String });
+    const TestModel = db.model('Test', schema);
+    TestModel.schema.virtual('myVirtual').get(function() {
+      return this.field + ' from myVirtual';
+    });
+    const doc = new TestModel({ field: 'Hello' });
+    assert.strictEqual(doc.myVirtual, undefined);
+
+    TestModel.recompileSchema();
+    assert.equal(doc.myVirtual, 'Hello from myVirtual');
+  });
 });