From 40b51709ff396efe40d2cd884c88e2b60cd5f03e Mon Sep 17 00:00:00 2001
From: Paolo Galeone <nessuno@nerdz.eu>
Date: Sun, 22 Nov 2015 21:48:32 +0100
Subject: [PATCH] Use the sql default value (of the tag field) when updating a
 field to a blank value

---
 callback_update.go | 12 +++++++++---
 structs_test.go    |  1 +
 update_test.go     | 18 ++++++++++++++++--
 3 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/callback_update.go b/callback_update.go
index b710f40e..e45a3a84 100644
--- a/callback_update.go
+++ b/callback_update.go
@@ -51,10 +51,16 @@ func Update(scope *Scope) {
 			fields := scope.Fields()
 			for _, field := range fields {
 				if scope.changeableField(field) && !field.IsPrimaryKey && field.IsNormal {
-					if !field.HasDefaultValue || !field.IsBlank {
-						sqls = append(sqls, fmt.Sprintf("%v = %v", scope.Quote(field.DBName), scope.AddToVars(field.Field.Interface())))
-					} else if field.HasDefaultValue {
+					if field.HasDefaultValue {
+						if field.IsBlank {
+							defaultValue := strings.Trim(parseTagSetting(field.Tag.Get("sql"))["DEFAULT"], "'")
+							sqls = append(sqls, fmt.Sprintf("%v = %v", scope.Quote(field.DBName), scope.AddToVars(defaultValue)))
+						} else {
+							sqls = append(sqls, fmt.Sprintf("%v = %v", scope.Quote(field.DBName), scope.AddToVars(field.Field.Interface())))
+						}
 						scope.InstanceSet("gorm:force_reload", true)
+					} else {
+						sqls = append(sqls, fmt.Sprintf("%v = %v", scope.Quote(field.DBName), scope.AddToVars(field.Field.Interface())))
 					}
 				} else if relationship := field.Relationship; relationship != nil && relationship.Kind == "belongs_to" {
 					for _, dbName := range relationship.ForeignDBNames {
diff --git a/structs_test.go b/structs_test.go
index 9a9b23d1..b52e64ef 100644
--- a/structs_test.go
+++ b/structs_test.go
@@ -134,6 +134,7 @@ type Animal struct {
 	unexported string    // unexported value
 	CreatedAt  time.Time
 	UpdatedAt  time.Time
+	Cool       bool `sql:"default:false"`
 }
 
 type JoinTable struct {
diff --git a/update_test.go b/update_test.go
index 71aa7c43..244e0dec 100644
--- a/update_test.go
+++ b/update_test.go
@@ -87,10 +87,11 @@ func TestUpdateWithNoStdPrimaryKeyAndDefaultValues(t *testing.T) {
 	DB.Save(&animal)
 	updatedAt1 := animal.UpdatedAt
 
+	// Sleep for a second and than update a field
+	time.Sleep(1000 * time.Millisecond)
 	DB.Save(&animal).Update("name", "Francis")
-
 	if updatedAt1.Format(time.RFC3339Nano) == animal.UpdatedAt.Format(time.RFC3339Nano) {
-		t.Errorf("updatedAt should not be updated if nothing changed")
+		t.Errorf("updatedAt should be updated when changing a field")
 	}
 
 	var animals []Animal
@@ -118,6 +119,19 @@ func TestUpdateWithNoStdPrimaryKeyAndDefaultValues(t *testing.T) {
 	if animal.Name == "" {
 		t.Errorf("Update a filed with an associated default value should not occur when trying to insert an empty field. The default one should be inserted\n")
 	}
+
+	// Animal.Cool has a default value thats equal to the Zero of its type. (false) I have to update this field to true and false without problems
+	animal.Cool = true
+	DB.Save(&animal)
+	if !animal.Cool {
+		t.Errorf("I should update a field with a default value to someother value")
+	}
+
+	animal.Cool = false
+	DB.Save(&animal)
+	if animal.Cool {
+		t.Errorf("I should update a field with an associated blank value to its blank value")
+	}
 }
 
 func TestUpdates(t *testing.T) {