Ruby on Rails执行rake db:migrate报can't modify frozen Hash错误

我参照教程配置Ruby on Rails数据库迁移，使用的Rake版本为13.0.6，运行rake db:migrate --trace时抛出如下错误，已尝试搜索线上解决方案未解决：

** Invoke db:migrate (first_time)
** Invoke db:load_config (first_time)
** Invoke environment (first_time)
** Execute environment
** Execute db:load_config
** Execute db:migrate
rake aborted!
FrozenError: can't modify frozen Hash: {:adapter=>"mysql2", :database=>"library_development", :username=>"root", :password=>["password"], :host=>"localhost"}
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-mysql2-adapter-0.0.3/lib/active_record/connection_adapters/mysql2_adapter.rb:11:in `mysql2_connection'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:882:in `public_send'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:882:in `new_connection'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:926:in `checkout_new_connection'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:905:in `try_to_checkout_new_connection'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:866:in `acquire_connection'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:588:in `checkout'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:428:in `connection'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/connection_adapters/abstract/connection_pool.rb:1128:in `retrieve_connection'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/connection_handling.rb:327:in `retrieve_connection'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/connection_handling.rb:283:in `connection'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/tasks/database_tasks.rb:237:in `migrate'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/railties/databases.rake:92:in `block (3 levels) in <main>'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/railties/databases.rake:90:in `each'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/activerecord-6.1.4.1/lib/active_record/railties/databases.rake:90:in `block (2 levels) in <main>'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/task.rb:281:in `block in execute'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/task.rb:281:in `each'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/task.rb:281:in `execute'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/task.rb:219:in `block in invoke_with_call_chain'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/task.rb:199:in `synchronize'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/task.rb:199:in `invoke_with_call_chain'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/task.rb:188:in `invoke'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/application.rb:160:in `invoke_task'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/application.rb:116:in `block (2 levels) in top_level'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/application.rb:116:in `each'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/application.rb:116:in `block in top_level'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/application.rb:125:in `run_with_threads'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/application.rb:110:in `top_level'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/application.rb:83:in `block in run'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/application.rb:186:in `standard_exception_handling'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/lib/rake/application.rb:80:in `run'
C:/Ruby30-x64/lib/ruby/gems/3.0.0/gems/rake-13.0.6/exe/rake:27:in `<top (required)>'
C:/Ruby30-x64/bin/rake:23:in `load'
C:/Ruby30-x64/bin/rake:23:in `<main>'
Tasks: TOP => db:migrate

相关配置文件 #

database.yml #

# SQLite. Versions 3.8.0 and up are supported.
#   gem install sqlite3
#
#   Ensure the SQLite 3 gem is defined in your Gemfile
#   gem 'sqlite3'
#
default: &default
  adapter: sqlite3
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  timeout: 5000

development:
  # <<: *default
  # database: db/development.sqlite3
  adapter: mysql2
  database: library_development
  username: root
  password: [password]
  host: localhost

# 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: db/test.sqlite3

production:
  <<: *default
  database: db/production.sqlite3

books.rb 迁移文件 #

class Books < ActiveRecord::Migration[6.1]
  def self.up
    create_table :books do |t|
       t.column :title, :string, :limit => 32, :null => false
       t.column :price, :float
       t.column :subject_id, :integer
       t.column :description, :text
       t.column :created_at, :timestamp
    end
  end

  def self.down
      drop_table :books
  end
end

subjects.rb 迁移文件 #

class Subjects < ActiveRecord::Migration[6.1]
  def self.up
      
    create_table :subjects do |t|
      t.column :name, :string
    end

    Subject.create :name => "Physics"
    Subject.create :name => "Mathematics"
    Subject.create :name => "Chemistry"
    Subject.create :name => "Psychology"
    Subject.create :name => "Geography"
  end

  def self.down
    drop_table :subjects
  end
end

MySQL权限配置说明 #

配置权限时，教程给出的授权语句中root处提示报错，内容大致为“root is not valid at this position for this server version”，因此没有使用教程提供的语句：

mysql> grant all privileges on library_development.*
to 'root'@'localhost' identified by 'password';
Query OK, 0 rows affected (0.00 sec)

实际执行的SQL语句为：

ALTER USER 'root'@'localhost' IDENTIFIED BY 'password';
GRANT ALL PRIVILEGES ON library_development.* TO 'root'@'localhost';

修复方案 #

错误根因有两个，和MySQL权限配置无关，你执行的权限语句是MySQL 8.0+的标准写法，没有问题：

1. database.yml密码格式错误：你写的password: [password]会被YAML解析为数组，而mysql2适配器需要字符串类型的密码，修改为password: "你的实际密码"即可，不要加方括号。
2. 依赖包冲突：你安装了废弃的activerecord-mysql2-adapter gem，Rails 6.1已经原生支持mysql2适配器，不需要额外安装该包。打开Gemfile删除gem 'activerecord-mysql2-adapter'相关行，仅保留gem 'mysql2', '~> 0.5'，执行bundle install更新依赖。

完成上述修改后重新运行rake db:migrate即可正常执行。

内容的提问来源于stack exchange，提问作者qccaprospect