ruby-on-rails - Rails 中的外键 - 错误

Question

我正在尝试向我的 Customers 表中添加一个新的外键列。这是我的迁移:

class AddCompanyForeignKeyToCustomers < ActiveRecord::Migration[5.1]
  def change
    add_reference :customers, :company, foreign_key: true
    add_foreign_key :customers, :companies
  end
end

这些是我遇到的错误:

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

这是什么意思？我不知道 fk_rails_$NUMBER 是什么。

Answer 1

这意味着您正在尝试创建一个复制您已有的外键约束。

此行在引用 companies 的 customers 上创建外键约束，并创建 company_id 列

add_reference :customers, :company, foreign_key: true

这一行又在尝试做外键约束

add_foreign_key :customers, :companies

只需删除一个或另一个，具体取决于您是否还需要添加 company_id 列