Update populate.md

Author: vkarpov15

docs/populate.md

@@ -554,67 +554,43 @@ comments[0].product.name; // "The Count of Monte Cristo"
 comments[1].blogPost.title; // "Top 10 French Novels"
 ```
 
-You could also assign a function to `refPath`, making it so that it
-selects a refpath depending on a value on the document being populated. For example.
+Defining separate `blogPost` and `product` properties works for this simple
+example. But, if you decide to allow users to also comment on articles or
+other comments, you'll need to add more properties to your schema. You'll
+also need an extra `populate()` call for every property, unless you use
+[mongoose-autopopulate](https://www.npmjs.com/package/mongoose-autopopulate).
+Using `refPath` means you only need 2 schema paths and one `populate()` call
+regardless of how many models your `commentSchema` can point to.
+
+You could also assign a function to `refPath`, which means Mongoose selects a refPath depending on a value on the document being populated.
 
 ```javascript
 const commentSchema = new Schema({
   body: { type: String, required: true },
-  verifiedBuyer: Boolean,
-  doc: {
+  commentType: {
+    type: String,
+    enum: ['comment', 'review']
+  },
+  entityId: {
     type: Schema.Types.ObjectId,
     required: true,
     refPath: function () {
-      return this.verifiedBuyer ? this.otherOption : this.docModel; // 'this' refers to the document being populated
+      return this.commentType === 'review' ? this.reviewEntityModel : this.commentEntityModel; // 'this' refers to the document being populated
     }
   },
-  docModel: {
+  commentEntityModel: {
     type: String,
     required: true,
     enum: ['BlogPost', 'Review']
   },
-  otherOption: {
+  reviewEntityModel: {
     type: String,
     required: true,
     enum: ['Vendor', 'Product']
   }
 });
-
-const Product = mongoose.model('Product', new Schema({ name: String }));
-const BlogPost = mongoose.model('BlogPost', new Schema({ title: String }));
-const Vendor = mongoose.model('Vendor', new Schema({ productType: String }));
-const Review = mongoose.model('Review', new Schema({ rating: String }));
-const Comment = mongoose.model('Comment', commentSchema);
-
-const book = await Product.create({ name: 'The Count of Monte Cristo' });
-const post = await BlogPost.create({ title: 'Top 10 French Novels' });
-
-const commentOnBook = await Comment.create({
-  body: 'Great read',
-  verifiedBuyer: true
-  doc: book._id,
-  docModel: 'Review',
-  otherOption: 'Product'
-});
-
-const commentOnPost = await Comment.create({
-  body: 'Very informative',
-  verifiedBuyer: false,
-  doc: post._id,
-  docModel: 'BlogPost',
-  otherOption: 'Vendor'
-});
-
 ```
 
-Defining separate `blogPost` and `product` properties works for this simple
-example. But, if you decide to allow users to also comment on articles or
-other comments, you'll need to add more properties to your schema. You'll
-also need an extra `populate()` call for every property, unless you use
-[mongoose-autopopulate](https://www.npmjs.com/package/mongoose-autopopulate).
-Using `refPath` means you only need 2 schema paths and one `populate()` call
-regardless of how many models your `commentSchema` can point to.
-
 <h2 id="dynamic-ref"><a href="#dynamic-ref">Dynamic References via <code>ref</code></a></h2>
 
 Just like `refPath`, `ref` can also be assigned a function.
@@ -631,10 +607,6 @@ const commentSchema = new Schema({
     }
   },
 });
-
-const Product = mongoose.model('Product', new Schema({ name: String }));
-const BlogPost = mongoose.model('BlogPost', new Schema({ title: String }));
-const Comment = mongoose.model('Comment', commentSchema);
 ```
 
 <h2 id="populate-virtuals"><a href="#populate-virtuals">Populate Virtuals</a></h2>