Defining indexes on field from embedded struct

[pboguslawski]

Given...

type ItemBase struct {
	ExternalID int      `gorm:"not null"`
	Name       string
}

type Item struct {
	ID     int      `gorm:"not null;primaryKey;autoIncrement"`
	ItemBase
        ItemHistory []*ItemHistory  // 1:n relation to history table.
}
type ItemHistory struct {
	ID    int `gorm:"not null;primaryKey;autoIncrement"`
	ItemID     int `gorm:"not null"`
	ItemBase
}

...is it possible to create with GORM unique index for ExternalID column in table for Item and not for ExternalID column in table for ItemHistory?

[pboguslawski]

When schema created by GORM from definition above already exists in DB, one may postprocess it with...

type Item struct {
    ExternalID int `gorm:"index:idx_items_externalid,unique"`
}
db.Migrator().CreateIndex(&Item{}, "idx_items_externalid")

...to have unique index on items.external_id only.

Is such postprocessing a canonical solution?