Document transaction for callbacks

README.md

@@ -560,7 +560,7 @@ db.Table("deleted_users").Pluck("name", &names)
 ## Callbacks
 
 Callback is a function defined to a struct, the function would be run when reflect a struct to database.
-If the function return an error, will prevent following operations. (for example, stop inserting, updating)
+If a function return error, gorm will prevent future operations and do rollback
 
 Those callbacks are defined now:
 
@@ -570,12 +570,21 @@ Those callbacks are defined now:
 `BeforeDelete`, `AfterDelete`
 
 ```go
+// Won't update readonly user
 func (u *User) BeforeUpdate() (err error) {
     if u.readonly() {
         err = errors.New("Read Only User")
     }
     return
 }
+
+// If have more than 1000 users, will rollback the insertion
+func (u *User) AfterCreate() (err error) {
+    if (u.Id > 1000) { // just an example, don't use Id to count users
+        err = errors.New("Only 1000 users allowed")
+    }
+    return
+}
 ```
 
 ## Specify Table Name

chain.go

@@ -132,22 +132,16 @@ func (s *Chain) Select(value interface{}) *Chain {
 }
 
 func (s *Chain) Save(value interface{}) *Chain {
-	do := s.do(value)
-	tx_started := do.begin()
+	do := s.do(value).begin()
 	do.save()
-	if tx_started {
-		do.commit()
-	}
+	do.commit_or_rollback()
 	return s
 }
 
 func (s *Chain) Delete(value interface{}) *Chain {
-	do := s.do(value)
-	tx_started := do.begin()
+	do := s.do(value).begin()
 	do.delete()
-	if tx_started {
-		do.commit()
-	}
+	do.commit_or_rollback()
 	return s
 }
 
@@ -156,12 +150,9 @@ func (s *Chain) Update(attrs ...interface{}) *Chain {
 }
 
 func (s *Chain) Updates(values interface{}, ignore_protected_attrs ...bool) *Chain {
-	do := s.do(s.value)
-	tx_started := do.begin()
-	do.setUpdateAttrs(values, ignore_protected_attrs...).update()
-	if tx_started {
-		do.commit()
-	}
+	do := s.do(s.value).begin().setUpdateAttrs(values, ignore_protected_attrs...)
+	do.update()
+	do.commit_or_rollback()
 	return s
 }
 

do.go

@@ -17,6 +17,7 @@ type Do struct {
 	db                 sql_common
 	guessedTableName   string
 	specifiedTableName string
+	startedTransaction bool
 
 	model   *Model
 	value   interface{}
@@ -756,20 +757,26 @@ func (s *Do) autoMigrate() *Do {
 	return s
 }
 
-func (s *Do) begin() bool {
+func (s *Do) begin() *Do {
 	if db, ok := s.db.(sql_db); ok {
 		tx, err := db.Begin()
 		if err == nil {
 			s.db = interface{}(tx).(sql_common)
-			return true
+			s.startedTransaction = true
 		}
 	}
-	return false
+	return s
 }
 
-func (s *Do) commit() {
-	if db, ok := s.db.(sql_tx); ok {
-		s.err(db.Commit())
+func (s *Do) commit_or_rollback() {
+	if s.startedTransaction {
+		if db, ok := s.db.(sql_tx); ok {
+			if s.chain.hasError() {
+				db.Rollback()
+			} else {
+				db.Commit()
+			}
+		}
 	}
 }
 

gorm_test.go

@@ -610,8 +610,12 @@ func (s *Product) AfterUpdate() {
 	s.AfterUpdateCallTimes = s.AfterUpdateCallTimes + 1
 }
 
-func (s *Product) AfterSave() {
+func (s *Product) AfterSave() (err error) {
+	if s.Code == "after_save_error" {
+		err = errors.New("Can't save")
+	}
 	s.AfterSaveCallTimes = s.AfterSaveCallTimes + 1
+	return
 }
 
 func (s *Product) BeforeDelete() (err error) {
@@ -622,8 +626,12 @@ func (s *Product) BeforeDelete() (err error) {
 	return
 }
 
-func (s *Product) AfterDelete() {
+func (s *Product) AfterDelete() (err error) {
+	if s.Code == "after_delete_error" {
+		err = errors.New("Can't delete")
+	}
 	s.AfterDeleteCallTimes = s.AfterDeleteCallTimes + 1
+	return
 }
 func (p *Product) GetCallTimes() []int64 {
 	return []int64{p.BeforeCreateCallTimes, p.BeforeSaveCallTimes, p.BeforeUpdateCallTimes, p.AfterCreateCallTimes, p.AfterSaveCallTimes, p.AfterUpdateCallTimes, p.BeforeDeleteCallTimes, p.AfterDeleteCallTimes}
@@ -703,6 +711,23 @@ func TestRunCallbacksAndGetErrors(t *testing.T) {
 	if db.Where("Code = ?", "dont_delete").First(&p3).Error != nil {
 		t.Errorf("Should not delete record due to errors happened in callback")
 	}
+
+	p4 := Product{Code: "after_save_error", Price: 100}
+	db.Save(&p4)
+	if err := db.First(&Product{}, "code = ?", "after_save_error").Error; err == nil {
+		t.Errorf("Record should be reverted if get an error after save", err)
+	}
+
+	p5 := Product{Code: "after_delete_error", Price: 100}
+	db.Save(&p5)
+	if err := db.First(&Product{}, "code = ?", "after_delete_error").Error; err != nil {
+		t.Errorf("Record should be found", err)
+	}
+
+	db.Delete(&p5)
+	if err := db.First(&Product{}, "code = ?", "after_delete_error").Error; err != nil {
+		t.Errorf("Record should be found because failed to delete", err)
+	}
 }
 
 func TestFillSmallerStructCorrectly(t *testing.T) {
@@ -1365,6 +1390,13 @@ func TestTransaction(t *testing.T) {
 	}
 }
 
+func (s *CreditCard) BeforeSave() (err error) {
+	if s.Number == "0000" {
+		err = errors.New("invalid credit card")
+	}
+	return
+}
+
 func BenchmarkGorm(b *testing.B) {
 	for x := 0; x < b.N; x++ {
 		email := BigEmail{Email: "benchmark@example.org", UserAgent: "pc", RegisteredAt: time.Now()}