From b3d60253658d9c6d27361e6ed06032c9c699d773 Mon Sep 17 00:00:00 2001
From: Jinzhu <wosmvp@gmail.com>
Date: Mon, 2 Mar 2015 10:52:18 +0800
Subject: [PATCH] Fix preload error when result is empty

---
 preload.go | 98 +++++++++++++++++++++++++++++-------------------------
 1 file changed, 52 insertions(+), 46 deletions(-)

diff --git a/preload.go b/preload.go
index 02e9eb38..7ca8ca55 100644
--- a/preload.go
+++ b/preload.go
@@ -34,62 +34,68 @@ func Preload(scope *Scope) {
 
 					switch relation.Kind {
 					case "has_one":
-						condition := fmt.Sprintf("%v IN (?)", scope.Quote(relation.ForeignDBName))
-						scope.NewDB().Where(condition, scope.getColumnAsArray(primaryName)).Find(results, conditions...)
+						if primaryKeys := scope.getColumnAsArray(primaryName); len(primaryKeys) > 0 {
+							condition := fmt.Sprintf("%v IN (?)", scope.Quote(relation.ForeignDBName))
+							scope.NewDB().Where(condition, primaryKeys).Find(results, conditions...)
 
-						resultValues := reflect.Indirect(reflect.ValueOf(results))
-						for i := 0; i < resultValues.Len(); i++ {
-							result := resultValues.Index(i)
-							if isSlice {
-								value := getRealValue(result, relation.ForeignFieldName)
-								objects := scope.IndirectValue()
-								for j := 0; j < objects.Len(); j++ {
-									if equalAsString(getRealValue(objects.Index(j), primaryName), value) {
-										reflect.Indirect(objects.Index(j)).FieldByName(field.Name).Set(result)
-										break
+							resultValues := reflect.Indirect(reflect.ValueOf(results))
+							for i := 0; i < resultValues.Len(); i++ {
+								result := resultValues.Index(i)
+								if isSlice {
+									value := getRealValue(result, relation.ForeignFieldName)
+									objects := scope.IndirectValue()
+									for j := 0; j < objects.Len(); j++ {
+										if equalAsString(getRealValue(objects.Index(j), primaryName), value) {
+											reflect.Indirect(objects.Index(j)).FieldByName(field.Name).Set(result)
+											break
+										}
 									}
+								} else {
+									scope.SetColumn(field, result)
 								}
-							} else {
-								scope.SetColumn(field, result)
 							}
 						}
 					case "has_many":
-						condition := fmt.Sprintf("%v IN (?)", scope.Quote(relation.ForeignDBName))
-						scope.NewDB().Where(condition, scope.getColumnAsArray(primaryName)).Find(results, conditions...)
-						resultValues := reflect.Indirect(reflect.ValueOf(results))
-						if isSlice {
-							for i := 0; i < resultValues.Len(); i++ {
-								result := resultValues.Index(i)
-								value := getRealValue(result, relation.ForeignFieldName)
-								objects := scope.IndirectValue()
-								for j := 0; j < objects.Len(); j++ {
-									object := reflect.Indirect(objects.Index(j))
-									if equalAsString(getRealValue(object, primaryName), value) {
-										f := object.FieldByName(field.Name)
-										f.Set(reflect.Append(f, result))
-										break
-									}
-								}
-							}
-						} else {
-							scope.SetColumn(field, resultValues)
-						}
-					case "belongs_to":
-						scope.NewDB().Where(scope.getColumnAsArray(relation.ForeignFieldName)).Find(results, conditions...)
-						resultValues := reflect.Indirect(reflect.ValueOf(results))
-						for i := 0; i < resultValues.Len(); i++ {
-							result := resultValues.Index(i)
+						if primaryKeys := scope.getColumnAsArray(primaryName); len(primaryKeys) > 0 {
+							condition := fmt.Sprintf("%v IN (?)", scope.Quote(relation.ForeignDBName))
+							scope.NewDB().Where(condition, primaryKeys).Find(results, conditions...)
+							resultValues := reflect.Indirect(reflect.ValueOf(results))
 							if isSlice {
-								value := getRealValue(result, associationPrimaryKey)
-								objects := scope.IndirectValue()
-								for j := 0; j < objects.Len(); j++ {
-									object := reflect.Indirect(objects.Index(j))
-									if equalAsString(getRealValue(object, relation.ForeignFieldName), value) {
-										object.FieldByName(field.Name).Set(result)
+								for i := 0; i < resultValues.Len(); i++ {
+									result := resultValues.Index(i)
+									value := getRealValue(result, relation.ForeignFieldName)
+									objects := scope.IndirectValue()
+									for j := 0; j < objects.Len(); j++ {
+										object := reflect.Indirect(objects.Index(j))
+										if equalAsString(getRealValue(object, primaryName), value) {
+											f := object.FieldByName(field.Name)
+											f.Set(reflect.Append(f, result))
+											break
+										}
 									}
 								}
 							} else {
-								scope.SetColumn(field, result)
+								scope.SetColumn(field, resultValues)
+							}
+						}
+					case "belongs_to":
+						if primaryKeys := scope.getColumnAsArray(relation.ForeignFieldName); len(primaryKeys) > 0 {
+							scope.NewDB().Where(primaryKeys).Find(results, conditions...)
+							resultValues := reflect.Indirect(reflect.ValueOf(results))
+							for i := 0; i < resultValues.Len(); i++ {
+								result := resultValues.Index(i)
+								if isSlice {
+									value := getRealValue(result, associationPrimaryKey)
+									objects := scope.IndirectValue()
+									for j := 0; j < objects.Len(); j++ {
+										object := reflect.Indirect(objects.Index(j))
+										if equalAsString(getRealValue(object, relation.ForeignFieldName), value) {
+											object.FieldByName(field.Name).Set(result)
+										}
+									}
+								} else {
+									scope.SetColumn(field, result)
+								}
 							}
 						}
 					case "many_to_many":