orm.go
func OptIndexTrackExistence(trackExistence bool) IndexOption {
	return func(options *IndexOptions) {
		options.trackExistence = trackExistence
		options.trackExistenceSet = true
	}
}
func OptIndexTrackExistence(trackExistence bool) IndexOption {
	return func(options *IndexOptions) {
		options.trackExistence = trackExistence
		options.trackExistenceSet = true
	}
}
// OptIndexTrackExistence enables keeping track of existence of columns.