ruby-on-rails - 如果 Ruby on Rails 中存在外键，如何删除它？

Question

ActionRecord 中有一个名为 index_exists? 的函数，但 Rails 4.2.7 上没有 foreign_key_exists?。

因此，当我在某些数据库上调用 remove_foreign_key :parties, :franchise_groups 时，它会崩溃。

我应该使用什么？

<小时/>

更新

我的代码

class RemoveForeignKey < ActiveRecord::Migration
  def up
    if foreign_key_exists?(:parties, :franchise_groups)
      remove_foreign_key :parties, :franchise_groups
    end
  end
end

报错

== 20161107163800 RemoveForeignKey: migrating =================================
-- foreign_key_exists?(:parties, :franchise_groups)
rake aborted!
An error has occurred, all later migrations canceled:

undefined method `foreign_key_exists?' for #<RemoveForeignKey:0x00000007ea0b58>
/home/rje/.rvm/gems/ruby-2.3.0/gems/activerecord-4.2.7/lib/active_record/migration.rb:664:in `block in method_missing'

Answer 1

but no foreign_key_exists?

There is foreign_key_exists? :)

Checks to see if a foreign key exists on a table for a given foreign key definition.

# Checks to see if a foreign key exists.
  foreign_key_exists?(:accounts, :branches)

# Checks to see if a foreign key on a specified column exists.
foreign_key_exists?(:accounts, column: :owner_id)

# Checks to see if a foreign key with a custom name exists.
foreign_key_exists?(:accounts, name: "special_fk_name")

或者，您可以使用 foreign_keys :

if foreign_keys(:table_name).include?(foreign_key_name)
  # do stuff
end