Describe the feature

实现手动灵活添加索引的 AddIndex 和 AddUniqueIndex 方法，像V1那样。

Motivation

旧项目使用gormV1，像下面这样添加索引：

a.DB.Model(&models.Like{}).Where("deleted_at IS NULL").AddUniqueIndex("like_idx_post_id_id", "post_id", "id")

现在想升级到V2，V2似是使用Migrator.CreateIndex, 但是索引这方面碰到了点问题：

  1. struct里要添加tag, 若在field上add多个不同索引；或者多个fields上添加same index 来建复合索引，结果tag会变得很长和很不直观，可读性降低。
  2. 若不另外添加index name，只添加index或uniqueIndex，然后CreateIndex时会查询有index的fields统一建立索引，也不能创多个自定义索引。
  3. 假如要添加的索引包括了gorm.Model里的id或者created_at等字段，那是否需要修改这些fields的tag？
  4. 如上代码中，若要添加索引的条件，目前貌似不能用。

因为要直观知道添加了哪些uniqueIndex和index 比较重要，而且数量也很大，都改成tag感觉杂乱不直观而且容易出问题。现在要满足以前的需求只能用原声sql创建，然而这次升级v2就是想优化V1 batchCreate时手动拼sql的问题。

万分感谢🙏！

Related Issues

https://github.com/go-gorm/gorm/issues/5075

Comment From: jinzhu

Hi

We are not going to bring back the AddIndex, AddUniqueIndex method, maybe you can create a customized model only for the migration with tag?

Thank you.

Comment From: XBreath

Hi

We are not going to bring back the AddIndex, AddUniqueIndex method, maybe you can create a customized model only for the migration with tag?

Thank you.

你好！ 感谢回复！ 能举个例子吗？

Comment From: yangcheng

Hi

We are not going to bring back the AddIndex, AddUniqueIndex method, maybe you can create a customized model only for the migration with tag?

Thank you.

@jinzhu can you explain the rationale for this choice? Index is not part of data model, but rather an optimization for particular database implementation/version. I understand support meta-data like index can cover majority use case but often we still need to fine-tune index. Thanks

Comment From: jinzhu

Suggest to write following code in your migration files, so you can use gorm with other migration tools like: https://github.com/golang-migrate/migrate

type UserForMigration struct {
  Name string `gorm:"size:255;index:idx_name"`
}

// Create index for Name field
db.Table("uses").Migrator().CreateIndex(&UserForMigration{}, "Name")