我試圖將新的外鍵列添加到我的Customers表中。這是我的移民:Rails中的外鍵 - 錯誤
class AddCompanyForeignKeyToCustomers < ActiveRecord::Migration[5.1]
def change
add_reference :customers, :company, foreign_key: true
add_foreign_key :customers, :companies
end
end
這是我得到的錯誤:
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:
PG::DuplicateObject: ERROR: constraint "fk_rails_ef51a916ef" for relation "customers" already exists
: ALTER TABLE "customers" ADD CONSTRAINT "fk_rails_ef51a916ef"
FOREIGN KEY ("company_id")
REFERENCES "companies" ("id")
ActiveRecord::StatementInvalid: PG::DuplicateObject: ERROR: constraint "fk_rails_ef51a916ef" for relation "customers" already exists
: ALTER TABLE "customers" ADD CONSTRAINT "fk_rails_ef51a916ef"
FOREIGN KEY ("company_id")
REFERENCES "companies" ("id")
PG::DuplicateObject: ERROR: constraint "fk_rails_ef51a916ef" for relation "customers" already exists
是什麼任何的意思呢?我不知道fk_rails_ $ NUMBER是什麼。