Rails 3.2 + ruby​​2 + mysql2 + NoMethodError：undefined方法`查詢'爲零：NilClass

Question

我們正在升級到
rails版本3.2.16。
Mysql的寶石：mysql2（0.3.14）
紅寶石2.0.0p247

當我運行耙分貝：遷移，我得到下面的異常：

NoMethodError: undefined method `query' for nil:NilClass: CREATE TABLE `recently_viewed_products` (`id` int(11) DEFAULT NULL auto_increment PRIMARY KEY, `gid` bigint NOT NULL, `product_id` int(11) NOT NULL, `viewed_time` int(11)) ENGINE=InnoDB/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:246:in `block in execute' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/connection_adapters/abstract_adapter.rb:280:in `block in log' 
/usr/lib/ruby/gems/2.0.0/gems/activesupport-3.2.16/lib/active_support/notifications/instrumenter.rb:20:in `instrument' 
/usr/lib/ruby/gems/2.0.0/gems/ar-octopus-0.8.0/lib/octopus/rails3/abstract_adapter.rb:19:in `instrument' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/connection_adapters/abstract_adapter.rb:275:in `log' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:246:in `execute' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/connection_adapters/mysql2_adapter.rb:213:in `execute' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/connection_adapters/abstract/schema_statements.rb:170:in `create_table' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/connection_adapters/abstract_mysql_adapter.rb:435:in `create_table' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:466:in `block in method_missing' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:438:in `block in say_with_time' 
/usr/lib/ruby/2.0.0/benchmark.rb:281:in `measure' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:438:in `say_with_time' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:458:in `method_missing' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:334:in `method_missing' 
/mnt/xxx/releases/20131218044833/db/migrate/20131202073728_create_recently_viewed_products.rb:5:in `up' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:370:in `up' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:410:in `block (2 levels) in migrate' 
/usr/lib/ruby/2.0.0/benchmark.rb:281:in `measure' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:410:in `block in migrate' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/connection_adapters/abstract/connection_pool.rb:129:in `with_connection' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:389:in `migrate' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:528:in `migrate' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:720:in `block (2 levels) in migrate' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:777:in `call' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:777:in `ddl_transaction' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:719:in `block in migrate' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:700:in `each' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:700:in `migrate' 
/usr/lib/ruby/gems/2.0.0/gems/ar-octopus-0.8.0/lib/octopus/migration.rb:82:in `migrate_with_octopus' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:570:in `up' 
/usr/lib/ruby/gems/2.0.0/gems/ar-octopus-0.8.0/lib/octopus/migration.rb:105:in `up_with_octopus' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/migration.rb:551:in `migrate' 
/usr/lib/ruby/gems/2.0.0/gems/ar-octopus-0.8.0/lib/octopus/migration.rb:97:in `migrate_with_octopus' 
/usr/lib/ruby/gems/2.0.0/gems/activerecord-3.2.16/lib/active_record/railties/databases.rake:193:in `block (2 levels) in <top (required)>' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/task.rb:236:in `call' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/task.rb:236:in `block in execute' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/task.rb:231:in `each' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/task.rb:231:in `execute' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/task.rb:175:in `block in invoke_with_call_chain' 
/usr/lib/ruby/2.0.0/monitor.rb:211:in `mon_synchronize' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/task.rb:168:in `invoke_with_call_chain' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/task.rb:161:in `invoke' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/application.rb:149:in `invoke_task' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/application.rb:106:in `block (2 levels) in top_level' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/application.rb:106:in `each' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/application.rb:106:in `block in top_level' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/application.rb:115:in `run_with_threads' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/application.rb:100:in `top_level' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/application.rb:78:in `block in run' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/application.rb:165:in `standard_exception_handling' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/lib/rake/application.rb:75:in `run' 
/usr/lib/ruby/gems/2.0.0/gems/rake-10.1.0/bin/rake:33:in `<top (required)>' 
/usr/bin/rake:23:in `load' 
/usr/bin/rake:23:in `<main>' 

的異常僅在爲非默認數據庫運行遷移時纔會出現。 這裏是我的移民：

ActiveRecord::Base.establish_connection("big_#{Rails.env}") 

create_table :recently_viewed_products do |t| 
    t.integer :gid, :null => false, :limit => 8 
    t.integer :product_id, :null => false 
    t.integer :viewed_time 
end 

add_index :recently_viewed_products, :gid 
add_index :recently_viewed_products, [:gid, :product_id], :unique=>true, :name => "UNIQUE" 

ActiveRecord::Base.establish_connection(Rails.env) 

讓我知道，如果我缺少什麼。

Answer 1

確保你把：

ActiveRecord::Base.establish_connection YOUR_DB

線的 '向上' 或 '變' 法外。以便在遷移類初始化時調用它，而不是在方法中調用它。我猜錯誤發生是因爲沒有足夠的時間來建立連接。

EG：

class AddBlahToBlah < ActiveRecord::Migration 
    ActiveRecord::Base.establish_connection "#{Rails.env}_foo" 

    def up 
    create_table ... 
    end 
end