genmai.go
func (db *DB) hasPKTag(field *reflect.StructField) bool {
	for _, tag := range db.tagsFromField(field) {
		if tag == "pk" {
			return true
		}
	}
	return false
}
func (db *DB) hasPKTag(field *reflect.StructField) bool {
	for _, tag := range db.tagsFromField(field) {
		if tag == "pk" {
			return true
		}
	}
	return false
}
// hasPKTag returns whether the struct field has the "pk" tag.