gorm FAQs

BeforeUpdate执行成功,但updated_at仍是时间字符串,写入数据库错误

(/app/Golang/blog/models/tag.go:75) 
[2019-12-04 23:27:41]  Error 1265: Data truncated for column 'updated_at' at row 1 

(/app/Golang/blog/models/tag.go:75) 
[2019-12-04 23:27:41]  [0.39ms]  UPDATE `blog_tag` SET `name` = '杂谈', `updated_at` = '2019-12-04 23:27:41'  WHERE (id=2)

问题的根源在GoPath/pkg/mod/github.com/jinzhu/gorm@v1.9.11/callback_update.go的ini函数中:
gorm:update_time_stamp 在 gorm:before_update 后执行了.

DefaultCallback.Update().Register("gorm:assign_updating_attributes", assignUpdatingAttributesCallback)
DefaultCallback.Update().Register("gorm:begin_transaction", beginTransactionCallback)
DefaultCallback.Update().Register("gorm:before_update", beforeUpdateCallback)
DefaultCallback.Update().Register("gorm:save_before_associations", saveBeforeAssociationsCallback)
DefaultCallback.Update().Register("gorm:update_time_stamp", updateTimeStampForUpdateCallback)
DefaultCallback.Update().Register("gorm:update", updateCallback)
DefaultCallback.Update().Register("gorm:save_after_associations", saveAfterAssociationsCallback)
DefaultCallback.Update().Register("gorm:after_update", afterUpdateCallback)
DefaultCallback.Update().Register("gorm:commit_or_rollback_transaction", commitOrRollbackTransactionCallback)

BeforeUpdate执行成功并设置updated_at为整形时间戳后, updateTimeStampForUpdateCallback执行又将updated_at设置成了时间字符串

// updateTimeStampForUpdateCallback will set `UpdatedAt` when updating
func updateTimeStampForUpdateCallback(scope *Scope) {
    if _, ok := scope.Get("gorm:update_column"); !ok {
        scope.SetColumn("UpdatedAt", scope.db.nowFunc())
    }
}

而created_at因为先判断了非空if createdAtField.IsBlank而没有这个bug:

// updateTimeStampForCreateCallback will set `CreatedAt`, `UpdatedAt` when creating
func updateTimeStampForCreateCallback(scope *Scope) {
    if !scope.HasError() {
        now := scope.db.nowFunc()

        if createdAtField, ok := scope.FieldByName("CreatedAt"); ok {
            if createdAtField.IsBlank {
                createdAtField.Set(now)
            }
        }

        if updatedAtField, ok := scope.FieldByName("UpdatedAt"); ok {
            if updatedAtField.IsBlank {
                updatedAtField.Set(now)
            }
        }
    }
}

解决方案

重新注册gorm:update_time_stamp事件,重写updateTimeStampForUpdateCallback方法:

...
db.Callback().Update().Replace("gorm:update_time_stamp", updateTimeStampForUpdateCallback);
...


// updateTimeStampForUpdateCallback will set `UpdatedAt` when updating
func updateTimeStampForUpdateCallback(scope *gorm.Scope) {
    if _, ok := scope.Get("gorm:update_column"); !ok {
        _ = scope.SetColumn("UpdatedAt", time.Now().Unix())
    }
}