diff --git a/src/main/java/com/example/springdatamongodb/Activity.java b/src/main/java/com/example/springdatamongodb/Activity.java
index 0b717a2..e640961 100644
--- a/src/main/java/com/example/springdatamongodb/Activity.java
+++ b/src/main/java/com/example/springdatamongodb/Activity.java
@@ -2,17 +2,22 @@
 
 import lombok.Builder;
 import lombok.Data;
+import lombok.NonNull;
 import org.bson.types.ObjectId;
 import org.springframework.data.annotation.Id;
 import org.springframework.data.mongodb.core.mapping.Document;
+import org.springframework.data.mongodb.core.mapping.DocumentReference;
+import org.springframework.data.mongodb.core.mapping.Field;
 
 @Data
-@Builder
 @Document(collection = "activities")
 public class Activity {
     @Id
     private ObjectId id;
 
-    private ObjectId engagementId;
+    @NonNull
+    @DocumentReference
+    @Field("engagementId")
+    private Engagement engagement;
 
 }
diff --git a/src/main/java/com/example/springdatamongodb/Engagement.java b/src/main/java/com/example/springdatamongodb/Engagement.java
index 8716bae..1c3ce07 100644
--- a/src/main/java/com/example/springdatamongodb/Engagement.java
+++ b/src/main/java/com/example/springdatamongodb/Engagement.java
@@ -2,23 +2,27 @@
 
 import lombok.Builder;
 import lombok.Data;
+import lombok.NonNull;
 import org.bson.types.ObjectId;
 import org.springframework.data.annotation.Id;
 import org.springframework.data.annotation.ReadOnlyProperty;
 import org.springframework.data.mongodb.core.mapping.Document;
 import org.springframework.data.mongodb.core.mapping.DocumentReference;
 
+import java.util.ArrayList;
 import java.util.List;
 
 @Data
-@Builder
 @Document(collection = "engagements")
 public class Engagement {
 
     @Id
     private ObjectId id;
 
+    @NonNull
+    private String name;
+
     @ReadOnlyProperty
     @DocumentReference(lookup="{'engagementId':?#{#self._id}}")
-    private List<Activity> activities;
+    private List<Activity> activities = new ArrayList<>();
 }
diff --git a/src/main/resources/application.properties b/src/main/resources/application.properties
index 98c5cc4..9406e67 100644
--- a/src/main/resources/application.properties
+++ b/src/main/resources/application.properties
@@ -1 +1,2 @@
 spring.mongodb.embedded.version=3.3.1
+logging.level.root=debug
\ No newline at end of file
diff --git a/src/test/java/com/example/springdatamongodb/EngagementRepositoryTest.java b/src/test/java/com/example/springdatamongodb/EngagementRepositoryTest.java
index 1190d08..5f92a66 100644
--- a/src/test/java/com/example/springdatamongodb/EngagementRepositoryTest.java
+++ b/src/test/java/com/example/springdatamongodb/EngagementRepositoryTest.java
@@ -1,5 +1,6 @@
 package com.example.springdatamongodb;
 
+import org.bson.types.ObjectId;
 import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.data.mongo.DataMongoTest;
@@ -19,15 +20,33 @@ public class EngagementRepositoryTest {
 
     @Test
     void should_return_engagement_with_activities() {
-        Engagement engagement = Engagement.builder().build();
+        Engagement engagement = new Engagement("Foo");
+        Engagement saved = engagementRepository.save(engagement);
+        Activity activity = new Activity(saved);
+        activityRepository.save(activity);
 
-        engagementRepository.save(engagement);
+        Optional<Engagement> byId = engagementRepository.findById(engagement.getId());
 
-        Activity activity = Activity.builder().engagementId(engagement.getId()).build();
+        assertThat(byId.get().getActivities()).isNotEmpty();
+    }
+
+    @Test
+    void tryCascadeTheParentWithManualId() {
+        Engagement engagement = new Engagement("Foo");
+        Activity activity = new Activity(engagement);
         activityRepository.save(activity);
 
         Optional<Engagement> byId = engagementRepository.findById(engagement.getId());
 
-        assertThat(byId.get().getActivities()).isNotEmpty();
+        assertThat(byId.get().getActivities()).isEmpty();
+    }
+
+    @Test
+    void tryCascadeTheParentWithoutId() {
+        Engagement engagement = new Engagement("Foo");
+        Activity activity = new Activity(engagement);
+        activityRepository.save(activity);
+
+        Optional<Engagement> byId = engagementRepository.findById(engagement.getId());
     }
 }