remove_reference和add_reference的向下迁移报告没有外键

Question

迁移此迁移

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

或迁移此迁移

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

抛出此错误：

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)

  

我的order_items表确实有order_id列（并且已被编入索引）并且我有orders表，但是为什么不是rails找到列order_id放下它？

我暂时解决了

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

但如果我必须向下迁移add_reference该怎么办？

Answer 1

order_items表包含order_id列和索引index_order_items_on_order_id。

但它没有外键，因为错误已明确说明。

如果存在如图所示，那么在数据库中进行交叉检查（有许多工具可用）。外键是 fk_rails_hash

形式的外键

在我的情况下，外键在不正确的导出转储期间丢失，当我导入sql_dump并将我的数据迁移到此数据库时，它们不存在，尽管保留了索引和列。

解决方案：

• 删除列并以正确的方式添加引用

  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