在我的迁移错误中添加参考答案

【问题标题】：Add reference in my migration error在我的迁移错误中添加参考
【发布时间】：2017-07-01 02:08:57
【问题描述】：

我使用 mysql 数据库创建 rails new demo_project 我的凭据没问题我使用 rake db:create 创建表

Created database 'demo_project_development'
Created database 'demo_project_test'

然后我生成一个表

rails g model Product name:string description:text inventory:integer 'price:decimal{7,2}' restocked_at:datetime

成功了

class CreateProducts < ActiveRecord::Migration[5.0]
  def change
    create_table :products do |t|
      t.string :name
      t.text :description
      t.integer :inventory
      t.decimal :price, precision: 7, scale: 2
      t.datetime :restocked_at

      t.timestamps
    end
  end
end

之后我生成一个迁移

rails g migration AddQtySoldToProducts qty_solid:integer

并创建它

class AddQtySoldToProducts < ActiveRecord::Migration[5.0]
  def change
    add_column :products, :qty_solid, :integer
  end
end

然后我创建另一个迁移

rails g migration AddRefNumToProducts ref_num:string:index

并创建它

class AddRefNumToProducts < ActiveRecord::Migration[5.0]
  def change
    add_column :products, :ref_num, :string
    add_index :products, :ref_num
  end
end

以及最后一次迁移

rails g migration AddStyleToProducts style:references

并创建这个

class AddStyleToProducts < ActiveRecord::Migration[5.0]
  def change
    add_reference :products, :style, foreign_key: true
  end
end

当我运行rake db:migrate 时出现错误

== 20170213061527 CreateProducts：迁移

-- create_table(:products) -> 0.1451s == 20170213061527 CreateProducts：迁移（0.1453s）==========================

== 20170213061805 AddQtySoldToProducts：迁移 ============================= -- add_column(:products, :qty_solid, :integer) -> 0.3441s == 20170213061805 AddQtySoldToProducts：迁移（0.3443s）====================

== 20170213061950 AddRefNumToProducts：正在迁移 ============================== -- add_column(:products, :ref_num, :string) -> 0.0964s -- add_index(:products, :ref_num) -> 0.4156s == 20170213061950 AddRefNumToProducts：迁移（0.5121s）=====================

== 20170213062130 AddStyleToProducts：迁移 =============================== -- add_reference(:products, :style, {:foreign_key=>true}) rake 中止！ StandardError: 发生错误，所有以后的迁移取消：

Mysql2::Error: 无法添加外键约束：ALTER TABLE products 添加约束 fk_rails_326a064677 外键 (style_id) 参考资料styles (id) /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/mysql2-0.4.5/lib/mysql2/client.rb:120:in _query' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/mysql2-0.4.5/lib/mysql2/client.rb:120:inblock in query' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/mysql2-0.4.5/lib/mysql2/client.rb:119:in handle_interrupt' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/mysql2-0.4.5/lib/mysql2/client.rb:119:inquery' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:218:in block in execute' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract_adapter.rb:589:inblock in log' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activesupport-5.0.1/lib/active_support/notifications/instrumenter.rb:21:in instrument' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract_adapter.rb:583:inlog' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:218:in execute' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/mysql/database_statements.rb:31:in执行' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:916:in add_foreign_key' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/schema_definitions.rb:623:inforeign_key' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/schema_definitions.rb:100:in add_to' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:826:inadd_reference' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:846:in block in method_missing' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:815:inblock in say_with_time' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:815:in say_with_time' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:835:inmethod_missing' /Users/cdasia-tsd/Desktop/demo_project/db/migrate/20170213062130_add_style_to_products.rb:3:in change' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:789:inexec_migration' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:773:in block (2 levels) in migrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:772:inblock in 迁移' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:398:in with_connection' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:771:inmigrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:951:in migrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1212:inblock 在 execute_migration_in_transaction' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1282:in ddl_transaction' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1211:inexecute_migration_in_transaction' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1184:in block in migrate_without_lock' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1183:ineach' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1183:in migrate_without_lock' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1132:inblock in 迁移' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1299:in with_advisory_lock' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1132:inmigrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1006:in up' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:984:inmigrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/tasks/database_tasks.rb:161:in migrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/railties/databases.rake:58:inblock（2 级）在 ' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/rake-12.0.0/exe/rake:27:in <top (required)>' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/bin/ruby_executable_hooks:15:ineval' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/bin/ruby_executable_hooks:15:in <main>' ActiveRecord::StatementInvalid: Mysql2::Error: Cannot add foreign key constraint: ALTER TABLEproductsADD CONSTRAINTfk_rails_326a064677FOREIGN KEY (style_id) REFERENCESstyles(id) /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/mysql2-0.4.5/lib/mysql2/client.rb:120:in_query' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/mysql2-0.4.5/lib/mysql2/client.rb:120:in block in query' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/mysql2-0.4.5/lib/mysql2/client.rb:119:inhandle_interrupt' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/mysql2-0.4.5/lib/mysql2/client.rb:119:in query' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:218:inblock 正在执行' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract_adapter.rb:589:in block in log' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activesupport-5.0.1/lib/active_support/notifications/instrumenter.rb:21:ininstrument' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract_adapter.rb:583:in log' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:218:inexecute' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/mysql/database_statements.rb:31:in execute' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:916:inadd_foreign_key' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/schema_definitions.rb:623:in foreign_key' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/schema_definitions.rb:100:inadd_to' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:826:in add_reference' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:846:inblock in method_missing' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:815:in block in say_with_time' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:815:insay_with_time' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:835:in method_missing' /Users/cdasia-tsd/Desktop/demo_project/db/migrate/20170213062130_add_style_to_products.rb:3:inchange' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:789:in exec_migration' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:773:inblock（2 级）在迁移' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:772:in block in migrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:398:inwith_connection' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:771:in migrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:951:inmigrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1212:in block in execute_migration_in_transaction' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1282:inddl_transaction' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1211:in execute_migration_in_transaction' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1184:inblock in migrate_without_lock' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1183:in each' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1183:inmigrate_without_lock' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1132:in block in migrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1299:inwith_advisory_lock' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1132:in migrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1006:inup' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:984:in migrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/tasks/database_tasks.rb:161:inmigrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/railties/databases.rake:58:in block (2 levels) in <top (required)>' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/rake-12.0.0/exe/rake:27:in' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/bin/ruby_executable_hooks:15:in eval' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/bin/ruby_executable_hooks:15:in'Mysql2::Error: 无法添加外键约束 /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/mysql2-0.4.5/lib/mysql2/client.rb:120:in _query' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/mysql2-0.4.5/lib/mysql2/client.rb:120:inblock in query' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/mysql2-0.4.5/lib/mysql2/client.rb:119:in handle_interrupt' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/mysql2-0.4.5/lib/mysql2/client.rb:119:inquery' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:218:in block in execute' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract_adapter.rb:589:inblock in log' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activesupport-5.0.1/lib/active_support/notifications/instrumenter.rb:21:in instrument' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract_adapter.rb:583:inlog' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:218:in execute' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/mysql/database_statements.rb:31:in执行' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:916:in add_foreign_key' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/schema_definitions.rb:623:inforeign_key' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/schema_definitions.rb:100:in add_to' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/schema_statements.rb:826:inadd_reference' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:846:in block in method_missing' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:815:inblock in say_with_time' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:815:in say_with_time' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:835:inmethod_missing' /Users/cdasia-tsd/Desktop/demo_project/db/migrate/20170213062130_add_style_to_products.rb:3:in change' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:789:inexec_migration' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:773:in block (2 levels) in migrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:772:inblock in 迁移' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:398:in with_connection' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:771:inmigrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:951:in migrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1212:inblock in execute_migration_in_transaction' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1282:in ddl_transaction' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1211:inexecute_migration_in_transaction' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1184:in block in migrate_without_lock' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1183:ineach' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1183:in migrate_without_lock' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1132:inblock in 迁移' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1299:in with_advisory_lock' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1132:inmigrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:1006:in up' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/migration.rb:984:inmigrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/tasks/database_tasks.rb:161:in migrate' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/activerecord-5.0.1/lib/active_record/railties/databases.rake:58:inblock（2 级）在 ' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/gems/rake-12.0.0/exe/rake:27:in <top (required)>' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/bin/ruby_executable_hooks:15:ineval' /Users/cdasia-tsd/.rvm/gems/ruby-2.3.3/bin/ruby_executable_hooks:15:in `' 任务：TOP => db:migrate（通过运行任务查看完整跟踪 --trace) TSD-Interns-MacBook-Pro:demo_project cdasia-tsd$

【问题讨论】：

styles 表是否已经存在？

标签： ruby-on-rails ruby ruby-on-rails-3 activerecord

【解决方案1】：

您没有styles 表。

【讨论】：

感谢兄弟，这是有道理的。我只是在我的参考中删除了外键 true :)

【解决方案2】：

是的，在运行此迁移之前，您应该创建 style 表，否则您会遇到同样的问题。

请看下面的链接可能对你有帮助-

add_reference link1

add_reference link2

注意：如果你在任何地方写 add_reference 那么请首先确保这个表应该存在，或者如果你想一起创建所有迁移，那么迁移顺序应该是引用表创建的第一个迁移之后运行具有 add_reference 的迁移。

【讨论】：