Merge branch 'getTobiasNielsen-patch-5'

Author: kamilmysliwiec

content/techniques/mongo.md

@@ -89,6 +89,27 @@ In case there are multiple owners, your property configuration should look as fo
 owners: Owner[];
 ```
 
+If you don’t intend to always populate a reference to another collection, consider using `mongoose.Types.ObjectId` as the type instead:
+
+```typescript
+@Prop({ type: { type: mongoose.Schema.Types.ObjectId, ref: 'Owner' } })
+// This ensures the field is not confused with a populated reference
+owner: mongoose.Types.ObjectId;
+```
+
+Then, when you need to selectively populate it later, you can use a repository function that specifies the correct type:
+
+```typescript
+import { Owner } from './schemas/owner.schema';
+
+// e.g. inside a service or repository
+async findAllPopulated() {
+  return this.catModel.find().populate<{ owner: Owner }>("owner");
+}
+```
+
+> info **Hint** If there is no foreign document to populate, the type could be `Owner | null`, depending on your [Mongoose configuration](https://mongoosejs.com/docs/populate.html#doc-not-found). Alternatively, it might throw an error, in which case the type will be `Owner`.
+
 Finally, the **raw** schema definition can also be passed to the decorator. This is useful when, for example, a property represents a nested object which is not defined as a class. For this, use the `raw()` function from the `@nestjs/mongoose` package, as follows:
 
 ```typescript