[英]How do I drop a foreign key if it exists in Ruby on Rails?
There's a function called index_exists?
有一个叫index_exists?
in ActionRecord, but no foreign_key_exists?
在 ActionRecord 中,但没有foreign_key_exists?
on Rails 4.2.7.在 Rails 4.2.7 上。
So when I call remove_foreign_key:parties, :franchise_groups
on some databases it breaks.因此,当我在某些数据库上调用remove_foreign_key:parties, :franchise_groups
时,它会中断。
What should I use?我应该使用什么?
Update更新
My code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
gives the error给出错误
== 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'
but no
foreign_key_exists?
但没有foreign_key_exists?
There is foreign_key_exists?
有foreign_key_exists?
:) :)
Checks to see if a foreign key exists on a table for a given foreign key definition. 检查表中是否存在用于给定外键定义的外键。
# 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")
Alternatively, you can use foreign_keys
: 或者,您可以使用foreign_keys
:
if foreign_keys(:table_name).include?(foreign_key_name)
# do stuff
end
在Rails 4上没有foreign_key_exists所以我提出了以下解决方案:
remove_foreign_key :events, column: :subscribers_selector_id if foreign_keys(:events).map(&:column).include?("subscribers_selector_id")
I think you can use something like this 我想你可以使用这样的东西
def up
remove_foreign_key :parties, column: :franchise_groups
end
def down
add_foreign_key :parties, :franchise_groups
end
它适用于连接:
ActiveRecord::Base.connection.foreign_key_exists?(:parties, :franchise_groups)
My Rails version doesn't seem to have "foreign_key_exists?" 我的Rails版本似乎没有“foreign_key_exists?” (Rails 4.2.6), so I'm using Array#any? (Rails 4.2.6),所以我使用的是Array#any? to search through the results from "foreign_keys" and determine whether a given foreign key exists: 搜索“foreign_keys”的结果并确定是否存在给定的外键:
foreign_keys("parties").any?{|k| k[:to_table] == "franchise_groups"}
You can use it as such: 您可以这样使用它:
if foreign_keys("parties").any?{|k| k[:to_table] == "franchise_groups"}
remove_foreign_key :parties, column: :franchise_group_id
end
Rails 7 adds if_exists
option to remove_foreign_key
in order to not raise an error when the foreign key is already removed. Rails 7 向remove_foreign_key
添加了if_exists
选项,以便在外键已被删除时不会引发错误。
Rails 7 adds if_not_exists
option to add_foreign_key
in order to not raise an error when the foreign key is already added. Rails 7 向add_foreign_key
添加了if_not_exists
选项,以便在已添加外键时不引发错误。
As a result, a migration can be written in the following way:因此,迁移可以按以下方式编写:
class RemoveFranchiseGroupForeignKeysFromParties < ActiveRecord::Migration
def up
remove_foreign_key :parties, :franchise_groups, if_exists: true
end
def down
add_foreign_key :parties, :franchise_groups, if_not_exists: true
end
end
Sources:资料来源:
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