diff --git a/lib/hydration/ObjectHydrator.ts b/lib/hydration/ObjectHydrator.ts
index 2f935e93e6fd..9090b77823ab 100644
--- a/lib/hydration/ObjectHydrator.ts
+++ b/lib/hydration/ObjectHydrator.ts
@@ -1,6 +1,6 @@
 import { AnyEntity, EntityData, EntityProperty, Primary } from '../typings';
 import { Hydrator } from './Hydrator';
-import { Collection, EntityAssigner, ReferenceType, wrap } from '../entity';
+import { Collection, EntityAssigner, ReferenceType } from '../entity';
 import { Utils } from '../utils';
 
 export class ObjectHydrator extends Hydrator {
@@ -75,18 +75,21 @@ export class ObjectHydrator extends Hydrator {
     }
   }
 
-  private createCollectionItem<T extends AnyEntity<T>>(prop: EntityProperty, value: Primary<T> | EntityData<T>): T {
-    if (Utils.isPrimaryKey(value)) {
-      return this.factory.createReference(prop.type, value);
-    }
+  private createCollectionItem<T extends AnyEntity<T>>(prop: EntityProperty, value: Primary<T> | EntityData<T> | T): T {
+    const meta = this.em.getMetadata().get(prop.type);
+
+    if (Utils.isPrimaryKey(value, meta.compositePK)) {
+      const ref = this.factory.createReference<T>(prop.type, value);
+      this.em.merge(ref);
 
-    const child = this.factory.create(prop.type, value as EntityData<T>);
+      return ref;
+    }
 
-    if (wrap(child).__primaryKey) {
-      this.em.merge(child);
+    if (Utils.isEntity<T>(value)) {
+      return value;
     }
 
-    return child;
+    return this.factory.create(prop.type, value as EntityData<T>);
   }
 
 }
diff --git a/lib/typings.ts b/lib/typings.ts
index f4dcf196c3e8..503331c64568 100644
--- a/lib/typings.ts
+++ b/lib/typings.ts
@@ -94,7 +94,7 @@ export type MongoEntity<T extends { _id: IPrimaryKey; id: string }> = AnyEntity<
 export type EntityClass<T extends AnyEntity<T>> = Function & { prototype: T };
 export type EntityClassGroup<T extends AnyEntity<T>> = { entity: EntityClass<T>; schema: EntityMetadata<T> | EntitySchema<T> };
 export type EntityName<T extends AnyEntity<T>> = string | EntityClass<T>;
-export type EntityData<T extends AnyEntity<T>> = { [K in keyof T]?: T[K] | Primary<T[K]> | CollectionItem<T[K]>[] } & Dictionary;
+export type EntityData<T extends AnyEntity<T>> = { [K in keyof T]?: T[K] | Primary<T[K]> | EntityData<T[K]> | CollectionItem<T[K]>[] } & Dictionary;
 
 export interface EntityProperty<T extends AnyEntity<T> = any> {
   name: string & keyof T;
diff --git a/tests/EntityManager.mongo.test.ts b/tests/EntityManager.mongo.test.ts
index 9740f98f00ab..d0dff315102d 100644
--- a/tests/EntityManager.mongo.test.ts
+++ b/tests/EntityManager.mongo.test.ts
@@ -789,10 +789,10 @@ describe('EntityManagerMongo', () => {
     const cachedAuthor = orm.em.merge(Author, cache);
     expect(cachedAuthor).toBe(cachedAuthor.favouriteBook.author);
     expect(Object.keys(orm.em.getUnitOfWork().getIdentityMap())).toEqual([
-      'BookTag-' + tag1.id,
-      'BookTag-' + tag3.id,
       'Author-' + author.id,
       'Book-' + book1.id,
+      'BookTag-' + tag1.id,
+      'BookTag-' + tag3.id,
     ]);
     expect(author).not.toBe(cachedAuthor);
     expect(author.id).toBe(cachedAuthor.id);