Clean up associations before Preload, close #3345

callbacks/preload.go

@@ -107,6 +107,16 @@ func preload(db *gorm.DB, rels []*schema.Relationship, conds []interface{}) {
 
 	fieldValues := make([]interface{}, len(relForeignFields))
 
+	// clean up old values before preloading
+	switch reflectValue.Kind() {
+	case reflect.Struct:
+		rel.Field.Set(reflectValue, reflect.New(rel.Field.FieldType).Interface())
+	case reflect.Slice, reflect.Array:
+		for i := 0; i < reflectValue.Len(); i++ {
+			rel.Field.Set(reflectValue.Index(i), reflect.New(rel.Field.FieldType).Interface())
+		}
+	}
+
 	for i := 0; i < reflectResults.Len(); i++ {
 		elem := reflectResults.Index(i)
 		for idx, field := range relForeignFields {

tests/helper_test.go

@@ -115,7 +115,7 @@ func CheckUser(t *testing.T, user User, expect User) {
 
 	t.Run("Pets", func(t *testing.T) {
 		if len(user.Pets) != len(expect.Pets) {
-			t.Errorf("pets should equal, expect: %v, got %v", len(expect.Pets), len(user.Pets))
+			t.Fatalf("pets should equal, expect: %v, got %v", len(expect.Pets), len(user.Pets))
 		}
 
 		sort.Slice(user.Pets, func(i, j int) bool {
@@ -137,7 +137,7 @@ func CheckUser(t *testing.T, user User, expect User) {
 
 	t.Run("Toys", func(t *testing.T) {
 		if len(user.Toys) != len(expect.Toys) {
-			t.Errorf("toys should equal, expect: %v, got %v", len(expect.Toys), len(user.Toys))
+			t.Fatalf("toys should equal, expect: %v, got %v", len(expect.Toys), len(user.Toys))
 		}
 
 		sort.Slice(user.Toys, func(i, j int) bool {
@@ -177,7 +177,7 @@ func CheckUser(t *testing.T, user User, expect User) {
 
 	t.Run("Team", func(t *testing.T) {
 		if len(user.Team) != len(expect.Team) {
-			t.Errorf("Team should equal, expect: %v, got %v", len(expect.Team), len(user.Team))
+			t.Fatalf("Team should equal, expect: %v, got %v", len(expect.Team), len(user.Team))
 		}
 
 		sort.Slice(user.Team, func(i, j int) bool {
@@ -195,7 +195,7 @@ func CheckUser(t *testing.T, user User, expect User) {
 
 	t.Run("Languages", func(t *testing.T) {
 		if len(user.Languages) != len(expect.Languages) {
-			t.Errorf("Languages should equal, expect: %v, got %v", len(expect.Languages), len(user.Languages))
+			t.Fatalf("Languages should equal, expect: %v, got %v", len(expect.Languages), len(user.Languages))
 		}
 
 		sort.Slice(user.Languages, func(i, j int) bool {
@@ -212,7 +212,7 @@ func CheckUser(t *testing.T, user User, expect User) {
 
 	t.Run("Friends", func(t *testing.T) {
 		if len(user.Friends) != len(expect.Friends) {
-			t.Errorf("Friends should equal, expect: %v, got %v", len(expect.Friends), len(user.Friends))
+			t.Fatalf("Friends should equal, expect: %v, got %v", len(expect.Friends), len(user.Friends))
 		}
 
 		sort.Slice(user.Friends, func(i, j int) bool {

tests/preload_test.go

@@ -31,6 +31,20 @@ func TestPreloadWithAssociations(t *testing.T) {
 	var user2 User
 	DB.Preload(clause.Associations).Find(&user2, "id = ?", user.ID)
 	CheckUser(t, user2, user)
+
+	var user3 = *GetUser("preload_with_associations_new", Config{
+		Account:   true,
+		Pets:      2,
+		Toys:      3,
+		Company:   true,
+		Manager:   true,
+		Team:      4,
+		Languages: 3,
+		Friends:   1,
+	})
+
+	DB.Preload(clause.Associations).Find(&user3, "id = ?", user.ID)
+	CheckUser(t, user3, user)
 }
 
 func TestNestedPreload(t *testing.T) {