Mysql2::Error: Table 'table_name' 不存在: SHOW FULL FIELDS FROM `table_name`

Question

我正在使用 rails 5.1.1 和 mysql 5.7。我有一个迁移类：

class CreateCompanies < ActiveRecord::Migration[5.1]
  def change
    create_table :companies do |t|
    t.string :ragione_sociale
    t.references :forma_giuridica, foreign_key: true
    t.string :telefono_fisso
    t.string :fax
    t.string :pec
    t.string :mail
    t.string :web_site
    t.string :cellulare_emergenze
    t.string :via_legale
    t.string :n_civico_legale
    t.string :citta_legale
    t.string :cap_legale
    t.string :provincia_legale
    t.string :regione_legale
    t.string :via_operativa
    t.string :n_civico_operativa
    t.string :citta_operativa
    t.string :cap_operativa
    t.string :provincia_operativa
    t.string :regione_operativa
    t.string :pi
    t.string :cf
    t.string :ateco_primo
    t.string :ateco_secondo
    t.string :ateco_altro
    t.timestamps
    end
  end
end

我有一个空模型calledny.rb和一个名为companies_controller.rb的控制器。

我的database.yml 是：

# MySQL. Versions 5.1.10 and up are supported.
#
# Install the MySQL driver
#   gem install mysql2
#
# Ensure the MySQL gem is defined in your Gemfile
#   gem 'mysql2'
#
# And be sure to use new-style password hashing:
#   http://dev.mysql.com/doc/refman/5.7/en/old-client.html
#
default: &default
  adapter: mysql2
  encoding: utf8
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  username: root
  password: Pipipopo09
  host: localhost
  port: 3300

development:
  <<: *default
  database: Pluto_Demetra_development

# Warning: The database defined as "test" will be erased and
# re-generated from your development database when you run "rake".
# Do not set this db to the same as development or production.
test:
  <<: *default
  database: Pluto_Demetra_test

# As with config/secrets.yml, you never want to store sensitive information,
# like your database password, in your source code. If your source code is
# ever seen by anyone, they now have access to your database.
#
# Instead, provide the password as a unix environment variable when you boot
# the app. Read http://guides.rubyonrails.org/configuring.html#configuring-a-database
# for a full rundown on how to provide these environment variables in a
# production deployment.
#
# On Heroku and other platform providers, you may have a full connection URL
# available as an environment variable. For example:
#
#   DATABASE_URL="mysql2://myuser:mypass@localhost/somedatabase"
#
# You can use this database configuration with:
#
#   production:
#     url: <%= ENV['DATABASE_URL'] %>
#
production:
  <<: *default
  database: Pluto_Demetra_production
  username: Pluto_Demetra
  password: <%= ENV['PLUTO_DEMETRA_DATABASE_PASSWORD'] %>

运行rails db:migrate时出现以下错误：

== 20170621125622 CreateCompanies: migrating ==================================
-- create_table(:companies)
rails aborted!
StandardError: An error has occurred, all later migrations canceled:

Mysql2::Error: Table 'pluto_demetra_development.companies' doesn't exist: SHOW FULL FIELDS FROM `companies`
C:/Users/gvieri.BSNSTRATEGIES/SitiRuby/Pluto_Demetra/db/migrate/20170621125622_create_companies.rb:3:in `change'
bin/rails:4:in `require'
bin/rails:4:in `<main>'
ActiveRecord::StatementInvalid: Mysql2::Error: Table 'pluto_demetra_development.companies' doesn't exist: SHOW FULL FIELDS FROM `companies`
C:/Users/gvieri.BSNSTRATEGIES/SitiRuby/Pluto_Demetra/db/migrate/20170621125622_create_companies.rb:3:in `change'
bin/rails:4:in `require'
bin/rails:4:in `<main>'
Mysql2::Error: Table 'pluto_demetra_development.companies' doesn't exist
C:/Users/gvieri.BSNSTRATEGIES/SitiRuby/Pluto_Demetra/db/migrate/20170621125622_create_companies.rb:3:in `change'
bin/rails:4:in `require'
bin/rails:4:in `<main>'
Mysql2::Error: Cannot add foreign key constraint
C:/Users/gvieri.BSNSTRATEGIES/SitiRuby/Pluto_Demetra/db/migrate/20170621125622_create_companies.rb:3:in `change'
bin/rails:4:in `require'
bin/rails:4:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

我该如何解决这个错误？

Answer 1

这可能是由 ActiveRecord::Migration[5.1] 引起的。当你想给companies表添加外键时，Migration会先读取表，但是不存在。

将迁移更改为 5.0 对我有用。

class CreateCompanies < ActiveRecord::Migration[5.0]
end

或者先去掉外键，以后手动添加外键：

class CreateCompanies < ActiveRecord::Migration[5.1]
  def change
    create_table :companies do |t|
      t.string :ragione_sociale
      t.references :forma_giuridica # without :foreign_key option
      # ...
    end

    # add foreign key here
    add_reference :companies, :forma_giuridica
  end
end

Answer 2

::Migration[5.0] 使用主键 int(11)

和

::Migration[5.1] 使用主键 bigint(20)

最常见的原因是在创建外键时，被引用的字段和外键字段都需要匹配：

• Engine 应该是相同的 e.g. InnoDB
• 数据类型应该相同，并且长度相同。
  例如VARCHAR(20) 或 INT(10) 无符号
• 排序规则应该相同。 例如utf8
• 唯一 - 外键应该引用引用表中唯一的字段（通常是私有的）。

Answer 3

如其他答案中所述，当您使用的 ActiveRecord::Migration 版本对目标 MySQL 表上的 id 字段的类型做出错误假设时，您可能会收到此错误。

特别是，从 5.1 版开始，ActiveRecord 假定 id 字段的类型为 bigint，而不是像以前的版本中那样类型为 int。

您可以通过在迁移中手动指定外键的目标字段为type: :int 来解决此问题，如下所示：

class MyMigration < ActiveRecord::Migration[5.2]
  def change
    create_table :my_new_table do |t|
      t.references :my_existing_table,
                   foreign_key: true,
                   type: :int
    end
  end
end