ruby-on-rails - remove_reference 和 add_reference 的向下迁移报告没有外键

Question

向上迁移这个迁移

def change
    remove_reference :order_items, :order, foreign_key: true
end

或向下迁移此迁移

def change
    add_reference :order_items, :order, foreign_key: true
end

抛出这个错误:

StandardError: An error has occurred, this and all later migrations canceled:

Table 'order_items' has no foreign key for {:to_table=>"orders"}
G:/Rails/learn_rails/db/migrate/20170222035809_move_order_items_under_restaurant_orders.rb:3:in `change'
G:/Rails/learn_rails/bin/rails:4:in `require'
G:/Rails/learn_rails/bin/rails:4:in `<top (required)>'
-e:1:in `load'
-e:1:in `<main>'
ArgumentError: Table 'order_items' has no foreign key for {:to_table=>"orders"}
G:/Rails/learn_rails/db/migrate/20170222035809_move_order_items_under_restaurant_orders.rb:3:in `change'
G:/Rails/learn_rails/bin/rails:4:in `require'
G:/Rails/learn_rails/bin/rails:4:in `<top (required)>'
-e:1:in `load'
-e:1:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

My order_items table does have order_id column (and it is indexed) and I do have orders table, but then why isn't rails finding the column order_id and dropping it?

我暂时解决了

remove_index :order_items, :order_id
remove_column :order_items, : order_id

但是如果我必须向下迁移 add_reference 我该怎么办？

Answer 1

order_items 表有 order_id 列和索引 index_order_items_on_order_id。

但它没有 FOREIGN KEY，因为错误已明确指出。

如果如图所示存在，请在数据库中进行交叉检查(有许多可用工具)。外键是 fk_rails_hash

形式的外键

在我的例子中，外键在不正确的导出转储期间丢失，当我导入那个 sql_dump 并将我的数据迁移到这个数据库时，它们不存在，尽管索引和列被保留了。

解决方案:

• 以正确的方式删除列和添加引用

  remove_index :order_items, :order_id
  remove_column :order_items, :order_id
  add_reference :order_items, :order, foreign_key: true
  
  # or add only the foreign the key constraint
  # i'm afraid it I would miss anything else doing so
  

• 如果缺少这么多外键，最佳解决方案

  # instead of whole sql_dump
  # export only the data
  
  rails db:migrate:reset
  
  # import only the data making sure the insert
  # happens in the right order as it may violate
  # foreign_key constraints that are newly added