Merge pull request #2243 from marcpicaud/patch-3

docs(mikroorm): add a caveat about serialization

Author: kamilmysliwiec

content/recipes/mikroorm.md

@@ -182,6 +182,27 @@ object.
 > still need CLI config with the full list of entities. On the other hand, we can
 > use globs there, as the CLI won't go thru webpack.
 
+
+#### Serialization
+
+> warning **Note** MikroORM wraps every single entity relation in a `Reference<T>` or a `Collection<T>` object, in order to provide better type-safety. This will make [Nest's built-in serializer](/techniques/serialization) blind to any wrapped relations. In other words, if you return MikroORM entities from your HTTP or WebSocket handlers, all of their relations will NOT be serialized.
+
+Luckily, MikroORM provides a [serialization API](https://mikro-orm.io/docs/serializing) which can be used in lieu of `ClassSerializerInterceptor`.
+
+```typescript
+@Entity()
+export class Book {
+  @Property({ hidden: true }) // Equivalent of class-transformer's `@Exclude`
+  hiddenField = Date.now();
+  
+  @Property({ persist: false }) // Similar to class-transformer's `@Expose()`. Will only exist in memory, and will be serialized.
+  count?: number;
+  
+  @ManyToOne({ serializer: value => value.name, serializedName: 'authorName' }) // Equivalent of class-transformer's `@Transform()`
+  author: Author;
+}
+```
+
 #### Request scoped handlers in queues
 
 > info **info** `@UseRequestContext()` decorator was added in v4.1.0