From 2a28986c8de6b3796b21a928fdb4b167b699577a Mon Sep 17 00:00:00 2001
From: Iosebyte <4988743+iosebyte@users.noreply.github.com>
Date: Wed, 14 Aug 2019 22:47:02 +0200
Subject: [PATCH] Fixes System.ArgumentException when GetAncestor returns the
 root node (#1125)

---
 src/EntityFramework/Hierarchy/HierarchyId.cs                  | 4 ++++
 .../UnitTests/Hierarchy/HierarchyIdUnitTests.cs               | 1 +
 2 files changed, 5 insertions(+)

diff --git a/src/EntityFramework/Hierarchy/HierarchyId.cs b/src/EntityFramework/Hierarchy/HierarchyId.cs
index 02b84d2ee2..f42b9d8fb9 100644
--- a/src/EntityFramework/Hierarchy/HierarchyId.cs
+++ b/src/EntityFramework/Hierarchy/HierarchyId.cs
@@ -97,6 +97,10 @@ public HierarchyId GetAncestor(int n)
             {
                 return new HierarchyId(null);
             }
+            else if (GetLevel() == n)
+            {
+                return new HierarchyId(PathSeparator);
+            }
             string hierarchyStr = PathSeparator +
                                   string.Join(PathSeparator, _nodes.Take(GetLevel() - n).Select(IntArrayToStirng))
                                   + PathSeparator;
diff --git a/test/EntityFramework/UnitTests/Hierarchy/HierarchyIdUnitTests.cs b/test/EntityFramework/UnitTests/Hierarchy/HierarchyIdUnitTests.cs
index 41a30246d2..bfce17aa27 100644
--- a/test/EntityFramework/UnitTests/Hierarchy/HierarchyIdUnitTests.cs
+++ b/test/EntityFramework/UnitTests/Hierarchy/HierarchyIdUnitTests.cs
@@ -21,6 +21,7 @@ public void Check_hierarchyid_functions()
             Assert.Equal(new HierarchyId("/1/2.1/3/").GetAncestor(2), new HierarchyId("/1/"));
             Assert.Equal(new HierarchyId("/1/").GetAncestor(2) == null, true);
             Assert.Equal(new HierarchyId("/1/").GetAncestor(2) == new HierarchyId(null), true);
+            Assert.Equal(new HierarchyId("/1/").GetAncestor(1), new HierarchyId("/"));
             Assert.Equal(new HierarchyId("/1/").IsDescendantOf(null), true);
             Assert.Equal(new HierarchyId("/1/").IsDescendantOf(new HierarchyId(null)), true);
             Assert.Equal(new HierarchyId("/1/2/").IsDescendantOf(new HierarchyId("/")), true);