From 8dfcab0f7fb829e70c6bf28743a99fa881e63cd4 Mon Sep 17 00:00:00 2001
From: Richard Knop <risoknop@gmail.com>
Date: Tue, 24 May 2016 00:54:51 +0800
Subject: [PATCH] Fixed an occurence of a panic while preloading non existent
 fields.

---
 callback_query_preload.go |  8 ++++-
 preload_test.go           | 64 +++++++++++++++++++++++++++++++++++----
 2 files changed, 65 insertions(+), 7 deletions(-)

diff --git a/callback_query_preload.go b/callback_query_preload.go
index a4b1cf1f..14cae907 100644
--- a/callback_query_preload.go
+++ b/callback_query_preload.go
@@ -28,6 +28,10 @@ func preloadCallback(scope *Scope) {
 		for idx, preloadField := range preloadFields {
 			var currentPreloadConditions []interface{}
 
+			if currentScope == nil {
+				continue
+			}
+
 			// if not preloaded
 			if preloadKey := strings.Join(preloadFields[:idx+1], "."); !preloadedMap[preloadKey] {
 
@@ -67,7 +71,9 @@ func preloadCallback(scope *Scope) {
 			// preload next level
 			if idx < len(preloadFields)-1 {
 				currentScope = currentScope.getColumnAsScope(preloadField)
-				currentFields = currentScope.Fields()
+				if currentScope != nil {
+					currentFields = currentScope.Fields()
+				}
 			}
 		}
 	}
diff --git a/preload_test.go b/preload_test.go
index 5c49ecc2..e2fb35ff 100644
--- a/preload_test.go
+++ b/preload_test.go
@@ -1288,17 +1288,23 @@ func TestNilPointerSlice(t *testing.T) {
 		t.Error(err)
 	}
 
-	want := Level1{Value: "Bob", Level2: &Level2{
-		Value: "en",
-		Level3: &Level3{
-			Value: "native",
+	want := Level1{
+		Value: "Bob",
+		Level2: &Level2{
+			Value: "en",
+			Level3: &Level3{
+				Value: "native",
+			},
 		},
-	}}
+	}
 	if err := DB.Save(&want).Error; err != nil {
 		t.Error(err)
 	}
 
-	want2 := Level1{Value: "Tom", Level2: nil}
+	want2 := Level1{
+		Value:  "Tom",
+		Level2: nil,
+	}
 	if err := DB.Save(&want2).Error; err != nil {
 		t.Error(err)
 	}
@@ -1321,6 +1327,52 @@ func TestNilPointerSlice(t *testing.T) {
 	}
 }
 
+func TestNilPointerSlice2(t *testing.T) {
+	type (
+		Level4 struct {
+			ID uint
+		}
+		Level3 struct {
+			ID       uint
+			Level4ID sql.NullInt64 `sql:"index"`
+			Level4   *Level4
+		}
+		Level2 struct {
+			ID      uint
+			Level3s []*Level3 `gorm:"many2many:level2_level3s"`
+		}
+		Level1 struct {
+			ID       uint
+			Level2ID sql.NullInt64 `sql:"index"`
+			Level2   *Level2
+		}
+	)
+
+	DB.DropTableIfExists(new(Level4))
+	DB.DropTableIfExists(new(Level3))
+	DB.DropTableIfExists(new(Level2))
+	DB.DropTableIfExists(new(Level1))
+
+	if err := DB.AutoMigrate(new(Level4), new(Level3), new(Level2), new(Level1)).Error; err != nil {
+		t.Error(err)
+	}
+
+	want := new(Level1)
+	if err := DB.Save(want).Error; err != nil {
+		t.Error(err)
+	}
+
+	got := new(Level1)
+	err := DB.Preload("Level2.Level3s.Level4").Last(&got).Error
+	if err != nil {
+		t.Error(err)
+	}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %s; want %s", toJSONString(got), toJSONString(want))
+	}
+}
+
 func toJSONString(v interface{}) []byte {
 	r, _ := json.MarshalIndent(v, "", "  ")
 	return r