我正在使用 act-as-taggable-on gem 。我似乎做的每件事都是正确的，但是每当我尝试创建标签时，我都会收到错误消息：
PG::UniqueViolation: ERROR: duplicate key value violates unique constraint "tags_pkey"
DETAIL: Key (id)=(2) already exists.
: INSERT INTO "tags" ("name") VALUES ($1) RETURNING "id"
(0.3ms) ROLLBACK
Completed 500 Internal Server Error in 973ms
ActsAsTaggableOn::DuplicateTagError - 'Untag' has already been taken: