✅ Test sample_relationshp model

dataservice/api/sample_relationship/models.py

@@ -115,10 +115,22 @@ def validate_sample_relationship(target):
     if not target:
         return
 
+    # Ensure relationship includes existing Samples
+    try:
+        parent_id = target.child.kf_id
+        child_id = target.parent.kf_id
+    except AttributeError:
+        raise DatabaseValidationError(
+            SampleRelationship.__tablename__,
+            "modify",
+            "Both parent sample and child sample must point to existing"
+            f" samples"
+        )
+
     # Check for reverse relation
     sr = SampleRelationship.query.filter_by(
-        parent_id=target.child.kf_id,
-        child_id=target.parent.kf_id,
+        parent_id=parent_id,
+        child_id=child_id,
     ).first()
 
     if sr:
@@ -130,7 +142,7 @@ def validate_sample_relationship(target):
             f"Parent: {sr.parent_id} -> Child: {sr.child_id}, already exists"
         )
 
-    # Check for parent = child 
+    # Check for parent = child
     if target.parent.kf_id == target.child.kf_id:
         raise DatabaseValidationError(
             SampleRelationship.__tablename__,